'^s^^'^/^s 79/10 Biological Services Program UPSEARC FWS/OBS-79/10 September 1979 Coastal Waterbird Colonies: CAPE ELIZABETH, MAINE TO VIRGINIA Lin Fish and Wildlife Service U.S. Department of the Interior The Biological Services Program was established within the U.S. Fish and Wildlife Service to supply scientific information and methodologies on key environmental issues that impact fish and wildlife resources and their supporting ecosystems. The mission of the program is as follows: • To strengthen the Fish and Wildlife Service in its role as a primary source of information on national fish and wild- life resources, particularly in respect to environmental impact assessment. • To gather, analyze, and present information that will aid decisionmakers in the identification and resolution of problems associated with major changes in land and water use. • To provide better ecological information and evaluation for Department of the Interior development programs, such as those relating to energy development. Information developed by the Biological Services Program is intended for use in the planning and decisionmaking process to prevent or minimize the impact of development on fish and wildlife. Research activities and technical assistance services are based on an analysis of the issues a determination of the decisionmakers involved and their information needs, and an evaluation of the state of the art to identify information gaps and to determine priorities. This is a strategy that will ensure that the products produced and disseminated are timely and useful. Projects have been initiated in the following areas: coal extraction and conversion; power plants; geothermal , mineral and oil shale develop- ment; water resource analysis, including stream alterations and western water allocation, coastal ecosystems and Outer Continental Shelf develop- ment; and systems inventory, including National Wetland Inventory, habitat classification and analysis, and information transfer. The Biological Services Program consists of the Office of Biological Services in Washington, D.C., which is responsible for overall planning and management; National Teams, which provide the Program's central scientific and technical expertise and arrange for contracting biological services studies with states, universities, consulting firms, and others; Regional Staff, who provide a link to problems at the operating level; and staff at certain Fish and Wildlife Service research facilities, who conduct inhouse research studies. FWS/OBS-79/10 September 1979 COASTAL WATERBIRD COLONIES: CAPE ELIZABETH, MAINE TO VIRGINIA by R. Michael Erwin Massachusetts Cooperative Wildlife Research Unit University of Massachusetts Amherst, Massachusetts 01003 Number: 14-16-0008-1186 Project Officer Ralph Andrews Coastal Ecosystems, Region 5 U.S. Fish and Wildlife Service One Gateway Center, Suite 700 Newton Corner, Massachusetts 02158 A contribution of the Massachusetts Cooperative Wildlife Research Unit, University of Massachusetts, Massachusetts Division of Fish and Wildlife. The Wildlife Management Institute, and the U.S. Fish and Wildlife Service cooperating. Performed for Coastal Ecosystems Project Office of Biological Services Fish and Wildlife Service U.S. Department of the Interior Washington, D.C. 20240 DISCLAIMER The opinions, findings, conclusions, or recommendations expressed in this report are those of the author and do not necessarily reflect the views of the Office of Biological Services, Fish and Wildlife Service, U.S. Department of the Interior, nor does mention of trade names or commercial products consti- tute endorsement or recommendation for use by the Federal Government. The correct citation for this report is: Erwin, R.M. 1979. Coastal waterbird coloniesrCape Elizabeth, Maine to Virginia, U.S. Fish and Wildlife Service, Biological Services Program, FWS/OBS-79/10. 212 pp. ii PREFACE This report is one of several recounting the results of 1976-1977 surveys of nesting colonies of egrets, herons, gulls, terns, and their allies in coastal areas along portions of the U.S. Atlantic, the Great Lakes, and the northern Gulf of Mexico. Publication of the results will aid resource managers. Moreover, the hope is that as citizens learn more about these wildlife resources, they will acquire a greater appreciation for the interrelationships among coastal processes and resources. Any suggestions or questions regarding this report should be directed to: Information Transfer Specialist National Coastal Ecosystems Team U.S. Fish and Wildlife Service NASA-SI idell Computer Complex 1010 Gause Boulevard Slidell, Louisiana 70458 or Regional Activities Leader Coastal Ecosystems U.S. Fish and Wildlife Service Newton Corner, Massachusetts 02158 11 1 EXECUTIVE SUMMARY This report describes colony distribution, species abundance, historical trends, nesting chronology, and census techniques for 28 species of seabirds and wading birds from Cape Elizabeth, Maine to the Virginia-North Carolina border. A parallel report has been prepared for the rocky, island bound coastal region of Nlaine north of Cape Elizabeth (Korschgen 1979). The loca- tion and composition of all colony sites in 1977 are depicted in an atlas (Ervn'n and Korschgen 1979). From May to July, 1976 and 1977, surveys of nesting colonies were conducted by a number of teams of well-qualified field biologists. Fixed- and rotary-wing aircraft were used extensively to locate, photograph, and inventory colonies. In addition, surface (foot, boat) censuses of nests and/or adults were rT;ade at many colonies and compared with aerial estimates. Standardized data forms with census instructions were provided to all participants. A total of 240,982 pairs of waterbirds was recorded at 512 colonies in 1977. Herring (75,709 pairs) and laughing gulls (64,662) and common terns (26,905), respectively, were the 3 most abundant of the 17 seabird species. The least abundant species were those at the limits of their breeding ranges (the nearctic black guillemots and common eiders, and southern sandwich and Caspian terns). The most abundant of the 11 wading bird species were snowy egrets (10,148 pairs), black-crowned night herons (9,009), and cattle egrets (6,515). Green herons and white ibises were the most rare. For the 10 coastal States, Virginia (54,423 pairs), New Jersey (53,389), and Niassachusetts (42,488) harbored the greatest numbers of nesting birds, respectively, while Connecticut (5,467) and New Hampshire (465) had the fewest. Relative abundance of waterbirds is positively correlated with wetland area, a crude measure of both feeding and nesting habitat. Most nesting colonies are located on barrier, marsh, or coastal islands. In the highly-developed coastal areas of New Jersey, Delaware, and Long Island, New York, a number of beach- and dune-nesting seabird species (herring gulls, terns, black skimmers) have shifted from their traditional beach habitat to marsh or dredged niaterial islands in adjacent embayments. Analysis of census techniques indicated that, in general, aerial methods are best for locating colonies, photography, and, under some conditions for estimating adults. Helicopters are considered to be more useful than fixed-wing aircraft because of their slow speed and ability to hover and land in small open areas. Cost factors, however, must be balanced with efficiency. A total nest count is the most accurate method of assessing populations, but may be disruptive to colonies and costly in terrris of time and personnel. As an alternative, nest counts can be taken at a number of sample colonies and used to generate conversion factors to be applied to aerial estimates from other colonies. Regression analysis of adult estimates versus nest counts indicated both marked variation among species and among censuses for a given species. This variation is attributable mainly to colony differences in vegetation density, adult attendance (due to time, tidal and climatic influences), and observer. In general, aerial counts often underestimate gulls and wading birds. IV Examination of historical nesting records (1900-1975) in each State revealed trends for many species. At the beginning of the century, breeding populations of many species had been reduced or extirpated in many coastal regions because of the millinery trade and egg collecting. With the protection of Federal lav/s, most species have recovered all of their former breeding range. Herring and great black-backed gulls have not only recovered, but have expanded their ranges into the Carol inas. There is some evidence of recent herring gull declines in New England, but numbers are rapidly increasing from New Jersey south. Numbers of Arctic, roseate, and common terns are decreasing in New England, with the latter two species also showing a recent reduction on Long Island. Where human encroachment has altered barrier island dunes and beaches most tern, gull, and black skimmer colonies have moved to marsh and dredge deposition islands. Despite this human pressure on beaches, the least tern appears to be stable in most areas, except Rhode Island. Cormorants are increasing throughout New England after years of persecution by fishermen. On Penikese Island, Leach's storm-petrels persist (the only colony in the study area) and common eiders recently have nested following introduction. Information on wading birds is limited but in general, all species have increased and expanded their ranges northward over the past 10-20 years. Numbers of snowy and cattle egrets and glossy ibises have increased rapidly. Black-crowned night herons seem to have increased in some States after earlier declines associated with pesticide contamination. One pair of white ibises bred in Virginia in 1977, a new breeding record for the northeast. Although great blue herons nest inland from Maine to Virginia, the only major coastal colonies that remain from earlier years occur along the Chesapeake Bay (note: Coastal colonies are also numerous in Maine north of Portland). For many species, nesting chronology varies from year to year and even from colony to colony. Most wading birds arrive in the northeast and nest earlier than seabirds. Great blue herons, black-crowned night herons, and great egrets initiate nesting often as early as late February and March. In contrast, cattle egrets are usually last with egg-laying often not occurring until June. The large gulls nest earlier than terns, sometimes usurping former tern nesting sites. Climatic influences such as cold, storms, floods, etc., often result in renesting which prolongs the nesting period and causes substantial yearly variation in both reproductive timing and success. In most years, May and June are the months of peak nesting activity for almost all waterbird species in the mid-Atlantic States. TABLE OF CONTENTS Page PREFACE iii EXECUTIVE SUMMARY iv TABLE OF CONTENTS vi TABLES ix FIGURES xii ACKNOWLEDGMENTS xiv ABSTRACT xv KEY WORDS xvi INTRODUCTION 1 COLONIAL WATERBIRD INVENTORY RESULTS-1977 3 BREEDING ABUNDANCE 3 HABITAT UTILIZATION 30 METHODS OF ASSESSING BREEDING POPULATION SIZE. 34 SAMPLING METHODS "WITHIN COLONY" 35 LARGE-SCALE, "AMONG COLONY" METHODS OF ASSESSING POPULATION SIZE 38 Efficiency of Aerial and Ground Methods 40 Aerial -Ground Comparisons 42 Species Correction Factors (Aerial-Ground) 44 Aerial Photography 50 POPULATION TRENDS OF WATERBIRDS, 1900-1977 53 MAINE 54 Seabirds 54 Wading Birds 54 ISLES OF SHOALS (MAINE-NEW HAMPSHIRE) 57 Seabirds 57 Wading Birds 57 MASSACHUSETTS 59 Seabirds 59 Wading Birds 61 VI Paae RHODE ISLAND 62 Seabirds 62 Wading Birds 62 CONNECTICUT 64 Seabirds 64 Wading Birds 64 NEW YORK 66 Seabirds 66 Wading Birds 68 NEW JERSEY 69 Seabirds 69 Wading Birds 71 DELAWARE 73 Seabirds 73 Wading Birds 73 MARYLAND 75 Seabirds 75 Wading Birds 75 VIRGINIA 79 Seabirds 79 Wading Birds 82 NESTING CHRONOLOGY 83 SEABIRDS 83 WADING BIRDS 95 SUMMARY Ill MAfJAGEMENT RECOMMENDATIONS 113 POPULATION EVALUATION 113 FEEDING HABITAT 113 HABITAT PRESERVATION AND MANAGEMENT 114 REFERENCES 115 APPENDIXES A Procedures for Using Sampling Methods in Determining Nest Densities 124 B Listing of Colony Nesting Data, 1900-1977 126 C Selected Bibliography of Nesting Records of Colonial Waterbirds, Portland, Maine to Back Bay, Virginia . . . 133 D Colony Site Listing: Maine (Cape Elizabeth, South)- Virginia, 1977 164 E Breeding Species in Maine (Cape Elizabeth, South), 1977 177 VI 1 Page F Breeding Species in New Hampshire, 1977 179 G Breeding Species in Massachusetts, 1977 180 H Breeding Species in Rhode Island, 1977 186 I Breeding Species in Connecticut, 1977 188 J Breeding Species in New York, 1977 190 K Breeding Species in New Jersey, 1977 196 L Breeding Species in Delaware, 1977 204 M Breeding Species in Maryland, 1977 205 N Breeding Species in Virginia, 1977 208 VI 1 1 TABLES Title Page 1 Colonial waterbirds nesting during 1976-1977, southern Maine to Virginia 2 2 Total nesting pairs and number of colonies of colonial waterbirds in 1977, southern Maine to Virginia 4 3 Nesting populations of seabirds and wading birds by States, 1977 5 4 Waterbird nesting populations in Maine (south of Cape Elizabeth), 1977 6 5 Waterbird nesting populations in New Hampshire, 1977 7 6 Waterbird nesting populations in Massachusetts, 1977 8 7 Waterbird nesting populations in Rhode Island, 1977 9 8 Waterbird nesting populations in Connecticut, 1977 10 9 Waterbird nesting populations in New York (Long Island), 1977 n 10 Waterbird nesting populations in New Jersey, 1977 12 11 Waterbird nesting populations in Delaware, 1977 13 12 Waterbird nesting populations in Maryland, 1977 14 13 Waterbird nesting populations in Virginia, 1977 15 14 Rank order of 10 northeast States in waterbird nesting population size, wetland area, and coastline length 17 15 Correlation measures between nesting waterbird numbers, wetland area, and coastline length in nine northeastern States (Maine excluded) 18 16 Mean colony size (nesting pairs) of selected species in the 10 northeastern States 29 17 Habitat utilization by nesting seabirds (S) and wading birds (W) in the 10 northeastern States 31 IC Recreational use along oceanfront beaches. Long Island, New York, to the eastern shore of Virginia 32 IX TABLES (Continued) Page 19 Total nest count accuracy in selected Massachusetts gull colonies 36 20 Comparison of two sampling techniques for estimating total nests in selected gull and heron colonies in Massachusetts and Rhode Island 37 21 Field investigators, 1976-1977 39 22 Cost analysis of fixed-wing aircraft, helicopter, and ground (boat-foot) censusing of waterbird colonies 41 23 Regression analysis of aerial estimates of adults versus nest counts in selected waterbird colonies 43 24 Comparisons of observer estimates of adults versus nest counts at nine Maine gull colonies, 31 May 1977 47 25 Comparisons of observer estimates of adults versus nest counts at 11 Massachusetts gull colonies, June 1977 48 26 Factors used to convert aerial estimates of adults into numbers of breeding pairs (nests) in a colony 49 27 Population trends of colonial birds in Maine (Cape Elizabeth, South) exclusive of the Isles of Shoals, 1900-1977 55 28 Population trends of colonial birds at the Isles of Shoals (Maine-New Ham.pshire), 1900-1977 53 29 Population trends of colonial birds in Massachusetts, 1900-1977 60 30 Population trends of colonial birds in Rhode Island, 1900-1977 53 31 Population trends of colonial birds in Connecticut, 1900-1977 65 32 Population trends of colonial birds in Mew York (Long Island), 1900-1977 67 33 Population trends of colonial birds in New Jersey, 1900-1977 70 34 Population trends of colonial birds in Delaware, 1900-1977 74 TABLES (Continued) Page 35 Population trends of colonial birds along the Atlantic coast of Maryland, 1900-1977 76 36 Population trends of colonial birds along the Chesapeake Bay of Maryland, 1900-1977 77 37 Population trends of colonial birds along the Atlantic coast of Virginia, 1900-1977 80 38 Population trends of colonial birds along the Chesapeake Bay of Virginia, 1900-1977 81 39 Reference codes for nesting chronology data 84 X 1 FIGURES Title 1 Nesting densities of waterbirds in nine northeastern States relative to wetland area 2 Location of major nesting colonies in southern Maine and New Hampshire, 1977 3 Location of major nesting colonies in Massachusetts, 1977 . . . 4 Location of major nesting colonies in Rhode Island, 1977. . . . 5 Location of major nesting colonies in Connecticut, 1977 . . , . 6 Location of major nesting colonies in Long Island, New York, 1977 7 Location of major nesting colonies in New Jersey, 1977 8 Location of major nesting colonies in Delaware, 1977 9 Location of major nesting colonies in Maryland, 1977 10 Location of major nesting colonies in Virginia, 1977 11 Aerial estimation of adults vs. nest counts at nine Maine gull colonies, 31 May 1977 12 Aerial estimation of adults vs. nest counts at 11 Massachusetts colonies, 1 and 6 June 1977 13 Aerial photograph of great blue heron colony at Poplar Island, Chesapeake Bay, Maryland, 22 June 1977 14 Aerial photograph of double-crested cormorant colony at rock south of Cat Island, Marblehead, Massachusetts, 24 June 1977. . 15 Nesting chronology of the double-crested cormorant 16 Nesting chronology of the great black-backed gull 17 Nesting chronology of the herring gull 18 Nesting chronology of the laughing gull 19 Nesting chronology of the gull-billed tern Pacje 16 20 21 22 23 24 25 26 27 28 45 46 51 52 85 87 88 89 90 XT 1 FIGURES (Continued) Page 20 Nesting chronology of the Forster's tern 91 21 Nesting chronology of the common tern 92 22 Nesting chronology of the Arctic tern 93 23 Nesting chronology of the roseate tern 94 24 Nesting chronology of the least tern 96 25 Nesting chronology of the royal tern 97 26 Nesting chronology of the sandwich tern 98 27 Nesting chronology of the Caspian tern 99 28 Nesting chronology of the black skimmer 100 29 Nesting chronology of the black guillemot 101 30 Nesting chronology of the great blue heron 102 31 Nesting chronology of the green heron 104 32 Nesting chronology of the little blue heron 105 33 Nesting chronology of the cattle egret 106 34 Nesting chronology of the great egret 107 35 Nesting chronology of the snov^y egret 108 36 Nesting chronology of the Louisiana heron 109 37 Nesting chronology of the black-crowned night heron HO 38 Nesting chronology of the glossy ibis 112 xm ACKNOWLEDGMENTS A great many people facilitated the preparation of this report. First and foremost, Wendell E. Dodge, Leader of the Massachusetts Cooperative Wild- life Research Unit deserves a great deal of credit for initiating the contract proposal and for his supervision throughout. Field support was provided by the following U.S. Fish and Wildlife Service (Region 5) personnel: C. Bolin, R. Bollengier, Jr., E. Ladd, and J. Goldsberry. Substantial amounts of his- torical data on breeding waterbirds were generously provided by A. Borror, P. A. and F. G. Buckley, M. A. Byrd, R. B. Clapp, W. H. Drury, D. C. Duffy, R. L. Ferren, E. J. Fisk, N. Proctor, J. Weske, and L. Wilcox. Also, refuge man- agers at Back Bay (VA), Blackwater (MD), Brigantine (NJ), Chincoteague (VA), Plum Island (MA), and Target Rock (NY) National Wildlife Refuges helped by providing data from their refuge files. Technical assistance and expertise were provided by M. Civello, B. Hendricks, J. Portnoy; and N. and L. Rowse. R. Andrews. W. Dodge, J. Lewis, J. Portnoy, D. Smith, and S. Patton made suggestions for improving the manu- script. The cover artwork is by Charlotte Adamson. W. H. Drury and E. J. Fisk deserve special acknowledgment for spurring interest in colonial waterbirds as a significant wildlife resource. XIV ABSTRACT In 1976 and 1977, seabird and wading bird nesting colonies were inven- toried along the northeast U.S. coast from Cape Elizabeth, ^!aine to the Virginia-North Carolina border as part of a study conducted by the Massa- chusetts Cooperative Wildlife Research Unit. A parallel study was conducted for the rocky, island bound coastal region of Maine north of Cape Elizabeth (Korschgen 1979). Colonies were surveyed and censused from Narch to July by teams of highly-qualified field biologists using aerial and ground-based methods. A total of about 240,982 pairs of waterbirds (28 species) nested at 512 colonies in 1977. The most abundant species, in order, were herring gulls, laughing gulls, common terns, great black-backed gulls, snowy egrets, and black-crowned night herons. Virginia and New Jersey harbored the largest populations of waterbirds and also had the greatest area of coastal wetland habitat. Wading birds usually arrive on the breeding ground and begin nesting as early as late February and March, much earlier than most seabirds which usually arrive in April (gulls) or May (terns). Substantial colony and yearly variation exists in nesting chronology, but usually most waterbird young have fledged by August. Evaluation of census techniques suggested that helicopters were the most useful way to inventory colonies over this large region but were costly on a per-hour basis. When aerial methods are employed, nest counts are required in a number of "sample" colonies to establish an adult-to-nest ratio. This ratio can then be applied to "correct" aerial estimates of adult numbers at other colonies. For some conspicuous species such as double-crested cormorants, great blue herons, great egrets, royal terns, and black skimmers, aerial photography can be effectively used to count nesting adults. Historical nesting information indicated that most waterbi rd populations had recovered from near extirpation caused by hunting in the ISOC's. While populations of cormorants, herring and great black-backed gulls, cattle and snowy egrets and glossy ibises are increasing, marked declines of Arctic, roseate, and common terns have been documented in New England and New York. Habitat alteration by oceanfront development, pollution, and competition with more aggressive gull species for suitable colony sites are probably causally related to this reduction. Because many colonies are located on land which is vulnerable to recrea- tion and development pressures, careful monitoring and protection of nesting waterbirds should be implemented. In addition to this report, an atlas has been prepared to include loca- tion and nesting data for all waterbird colonies inventoried in 1977 from the Maine-Canada border to Virginia (Erwin and Korschgen 1979). The atlas is comprised of a series of maps showing individual colony sites and each map is accompanied by a set of Tables with details of the nesting species and charac- teristics of the colony sites. XV KEY WORDS Coastal Connecticut Populations Nesting colonies New York Habitat Seabirds New Jersey Protection Wading birds Delaware Barrier islands Waterbirds Maryland Cormorants Northeast Virginia Gulls Maine Helicopter Terns New Hampshire Survey Skimmers Massachusetts Inventory Herons Rhode Island Census Egrets Chronology Ibises XVI INTRODUCTION Colonial waterbirds are a conspicuous and significant part of the coastal environment. Even so, little effort has been made to evaluate present breeding waterbird populations on a regional level and to compare these with historical population levels. This report increases our knowl- edge about nesting chronology, present abundance, population trends, and colony distribution for 28 species of gulls, terns, skimmers, cormorants, herons, egrets, ibises, and eiders along the northeastern U.S. coast (Table 1). This report accompanies an atlas that includes locations of all colonies and Tables showing the results of the 1977 inventory (Erwin and Korschgen 1979). The study objectives were to: 1) inventory nesting waterbird colonies in 1976 and 1977, 2) evaluate survey and census methods, 3) examine histor- ical nesting records (1900 to present), 4) describe nesting chronology, 5) make management recommendations for the conservation and protection of nesting colonies. Table 1. Colonial waterbirds nesting during 1976-1977, southern Maine to Virginia. Common name Scientific name Leach's storm-petrel Double-crested cormorant Great blue heron Green heron Little blue heron Cattle egret Great egret Snowy egret Louisiana heron Black-crowned night heron Yellow-crowned night heron Glossy ibis White ibis Common eider Great black-backed gull Herring gull Laughing gull Gull -billed tern Forster's tern Common tern Arctic tern Roseate tern Least tern Royal tern Sandwich tern Caspian tern Black skimmer Black guillemot Oceanodroma leucorhoa Phalacrocorax auritus Ardea herodias Butorides striatus Florida caerulea Bubulcus ibis Casmerodius albus Eqretta thula Hydranassa tricolor Nycticorax nycticorax Nyctanassa violacea Plegadis falcinellus Eudocimus albus Somateria mollissima Larus marinus Larus argentatus Larus atricil la Gelochelidon nilotica Sterna forsteri Sterna hirundo Sterna paradisaea Sterna dougallii Sterna albifrons Sterna maxima Sterna sandvicensis Sterna caspia Rynchops niqer Cepphus grylle COLONIAL WATERBIRD INVENTORY RESULTS - 1977 BREEDING ABUNDANCE The results from all aerial and ground inventories conducted in 1977 are summarized in Tables 2 through 13. Table 2 shows the order of abundance for all seabirds and wading birds for the entire study area (southern Maine to the Virginia-North Carolina border). Table 3 summarizes nesting populations of the two major waterbird groups in each of the 10 States. Subsequent tables show by State the species nesting in 1977, the numbers of colonies, total pairs, and mean colony sizes. The three species of gulls rank 1, 2, and 4 in seabird abundance along the northeast coast (Table 2). This is somewhat expected considering their opportunistic feeding habits, physical dominance of smaller seabirds, and (at least for herring gulls), plasticity in nest and colony site selection (Burger 1977). The laughing gull is much more restricted to its nesting habitat than the other two gulls, and concentrates in the salt marshes of southern New Jersey and along the eastern shore of Virginia. Only at small, scattered colonies in Maine and Massachusetts does the laughing gull nest at upland sites. Their current northern populations are a mere remnant of those present in the 1800's in New York (Bent 1963a, Griscom 1923) and during the early 1900's in Massachusetts (Nisbet 1971a, b). The small number of Arctic, gull-billed, sandwich, and Caspian terns. Leach's storm-petrels, black guillemots, and common eiders were found because they are near range limits, i.e., petrels, eiders, guillemots, and Arctic terns are nearctic species and are more abundant in northern Maine and Canada, while the other species are much more common along the Gulf of Mexico and/or South Atlantic coasts. Snowy egrets and black-crowned night herons are the most abundant and widely-distributed of the wading birds. Interestingly, the two recent invad- ing species (cattle egret and glossy ibis) are the next most numerous. Cattle egrets, however, are only common in colonies south of New York. Green herons are much more numerous than indicated in the Table, since only those pairs found in mixed-species heronries are reported. They often nest in small groups or as solitary pairs along the entire coast. The v/hite ibis appears to be expanding its range northward and a pair nested for the first time at Fishermans Island, Virginia in 1977 (P. Frohring pers. comm.). State totals of nesting seabirds and wading birds show that Virginia and New Jersey harbor the largest numbers (Table 3), but the relative numbers (density per unit of wetland) are greatest in Rhode Island, New York, and Massachusetts, respectively (Figure 1). Further study is required to deter- mine if these density differences result from nesting habitat and/or food availability differences among States. Wading birds comprise the larger proportion of waterbird abundance in the more southern States (Figure 1), probably because of the correlation between wading bird abundance and wetland area (Tables 14 and 15, Custer and Osborn 1977). Most wading birds feed predominantly in coastal marshes, pools, and tidal flats; thus, their density is expected to be rriore closely correlated Table 2. Total nesting pairs and number of colonies of colonial waterbirds in 1977, southern Maine to Virginia. Number of Species nesting pairs Colonies^ Seabirds 212 57 186 149 118 3 48 18 24 34 6 7 1 1 1 1 1 84 93 25 62 20 59 43 36 33 21 1 Herring gull 75,709 Laughing gul 1 64,662 Common tern 26,905 Great black-backed gull 10,838 Least tern 7,616 Royal tern 4,734 Black skimmer 4,247 Double-crested cormorant 2,676 Roseate tern 2,278 Forster's tern 2,078 Gull-billed tern 124 Arctic tern 73 Leach's storm-petrel 20 Sandwich tern 5 Black gui 1 lemot 3 Caspian tern 1 Common eider 1 Wading birds Snowy egret 10,148 Black-crowned night heron 9,009 Cattle egret 6,515 Glossy ibis 5,491 Great blue heron 2,653 Great egret 2,474 Little blue heron 1,213 Louisiana heron 1,166 Yellow-crowned night heron 256 Green heron'^ 86 White ibis 1 Total 240,982 a b Includes all colonies at which no estimates were made. Incomplete census. Table 3. Nesting populations of seabirds and wading birds, by States, 1977. State Seabirds Wading birds Total pairs Virginia 46,731 7,692 54,423 New Jersey 44,676 8,713 53,389 Massachusetts 39,922 2,566 42,488 New York 33,619 4,247 37,866 Maryland 9,535 6,844 16,379 Maine^ 14,097 202 14,299 Rhode Island 7,193 1,026 8,219 Delaware 771 7,216 7,987 Connecticut 4,961 506 5,467 New Hampshire 465 0 465 Totals 201,970 39,012 240,982 ^ From Cape Elizabeth, Maine south. Table 4. Waterbird nesting populations in Maine (south of Cape Elizabeth), 1977. No. Total Mean Standard colonies breeding pairs colony size deviation Species Double-crested 5 827 165 cormorant Little blue heron 2 4 2 Snowy egret 3 84 28 Louisiana heron 1 1 1 Black-crowned night 4 38 9 heron Glossy ibis 3 75 25 Great black-backed 16 3,280 205 gull Herring gull 17 9,751 574 Common tern 2 197 98 Roseate tern 1 25 25 Least tern 1 14 14 Black guillemot 1 3 3 152 2 22 8 11 296 633 76 Table 5. Waterbird nesting populations in New Harrpshire, 1977. Species CO No. lonies Total breeding pa irs col Mean ony size St, de' andard i/iation Double-crested cormorant 1 24 24 0 Great black-backed gull 2 91 45 43 Herring gull 3^ 350 175 71 Includes one site at which species may breed but for which an estimate is not available. Table 6. Waterbird nesting populations in Massachusetts, 1977. No. Total Mean St andard Species co lonies breeding pairs colony size de viation Leach's storm-petrel^ 1 20+ 20 - Double-crested 11 1,760 160 144 cormorant Green heron 1 1 1 - Little blue heron 4 19 4 1 Cattle egret 1 10 10 - Great egret 3 6 2 2 Snowy egret 12 459 38 60 Louisiana heron 1 1 1 - Black-crowned night 14 1,958 140 169 heron Glossy ibis 3^ 112 56 72 Common eider^ 1 1 + 1 - Great black-backed 50 4,670 93 171 gull Herring gul 1 61 25,845 424 739 Laughing gull 1 200 200 - Common tern 30 4,475 149 388 Arctic tern 7 73 10 13 Roseate tern 6 1,327 221 368 Least tern 32 1,551 48 63 ^ Based on previous years' estimates. Includes one colony site at which the species may breed but for which no estimate is available. Probably an introduced pair. Table 7. Waterbird nesting populations 1n Rhode Island, 1977. No, Total Mean Standard Species colonies breeding pairs colony size deviation Green heron 2 2 1 0 Little blue h( jron 2' 35 35 - Cattle egret 1 110 110 - Great egret 2' 22 22 - Snowy egret 2' 180 180 Black-crowned night 4 517 129 215 heron Glossy ibis 1 160 160 - Great black-backed 14^ 540 45 60 gull Herring gul 1 15 6,016 401 639 Common tern 22^ 589 29 24 Roseate tern 5<^ 1 1 - Least tern 4^ 47 16 19 Includes one colony site at which the species may breed but for which no estimate is available. Includes 2 colony sites at which the species may breed but for which no estimates are available. Includes 4 colony sites at which the species may breed but for which no estimates are available. Table 8. Waterbird nesting populations in Connecticut, 1977. No. Total Mean Standard Species colonies breeding pairs colony size deviation Green heron 2 15 8 4 Little blue heron 1 1 1 - Cattle egret 1 4 4 - Great egret 1 20 20 - Snowy egret 1 50 50 - Black-crowned night 2 406 203 279 heron Yellow-crowned night 1^ - - - heron Glossy ibis 1 10 10 - Great black-bai eked 13 164 13 16 gull Herring gull 30 3,134 104 334 Common tern 11 1,479 134 322 Roseate tern 3 64 21 25 Least tern 4^ 120 40 9 Includes one colony site at which the species may breed but for which no estimate is available. 10 Table 9. Waterbird nesting populations in New York (Long Island), 1977. No. Total Mean Standard Species co' lonies breeding pairs colony size deviation Double-crested 1 65 65 ^^ cormorant Green heron 3 3 1 0 Little blue heron 6^ 13 3 2 Cattle egret 1 15 15 - Great egret 14 317 22 36 Snowy egret 17 1,416 83 75 Louisiana heron 5^ 10 2 1 Black-crowned night 19 1,534 81 51 heron Yellow-crowned night 5 22 4 4 heron Glossy ibis 15 917 61 94 Great black-backed 26 1,894 73 231 gull Herring gul 1 31 17,459 563 855 Common tern 38 10,014 263 500 Roseate tern 9 861 96 264 Least tern 36 2,884 80 139 Black skimmer 9 442 49 57 ^ Includes two colony sites at which the species may breed but for which no estimates are available. Includes one colony site at which the species may breed but for which no estimate is available. 11 Table 10. Waterbird nesting populations in New Jersey, 1977. No. Total Mean Standard Species co lonies breeding pairs colony size deviation Great blue heron 3 3 - Green heron 14 4 4 Little blue heron 17^ 246 15 20 Cattle egret 565 81 84 Great egret 17^ 488 30 68 Snowy egret 24 2,783 116 175 Louisiana heron 11 178 16 17 Black-crowned night 26 1,453 56 73 heron Yellow-crowned night 16^ 139 9 11 heron Glossy ibis 19 2,844 149 263 Great black-backed 22 144 7 6 gull Herring gul 1 34 5,913 174 329 Laughing gull 25 30,940 1,238 2,273 Gull-billed tern 4 19 5 3 Forster's tern 6 463 77 86 Common tern 44 4,462 101 181 Least tern 19 1,786 94 95 Black skimmer 13 949 73 121 ^ Includes one colony site at which the species may breed but for which no estimate is available. 12 Table 11. Waterbird nesting populations in Delaware, 1977. Species No. Total Mean Standard colonies breeding pairs colony size deviation Great blue heron 3 174 58 Green heron 2 2 Little blue heron 600 600 Cattle egret 4,000 4,000 Great egret 250 250 Snowy egret 1,000 1,000 Louisiana heron 50 50 Black-crowned night 400 400 heron Ye 1 low- crowned night 40 40 heron Glossy ibis 700 700 Herring gull 31 31 Laughing gull 96 96 Common tern 451 75 Least tern 166 41 Black skimmer 27 7 74 68 35 4 13 Table 12. Waterbird nesting populations in Maryland, 1977, No. Total Mean Standard Species colonies breeding pairs colony size deviation Great blue heron 14 1,883 135 130 Green heron 3 28 9 6 Little blue heron 2 102 51 8 Cattle egret 6 1,325 221 364 Great egret 12 830 69 96 Snowy egret 11 1,332 121 105 Louisiana heron 5 204 41 11 Black-crowned night 11 966 88 104 heron Yellow-crowned night 6 37 6 5 heron Glossy ibis 7 137 20 20 Great black-backed 4 33 8 11 gull Herring gull 10 4,586 459 997 Laughing gull 2 2,229 1,114 1,365 Forster's tern 7 520 74 70 Common tern 11 1,682 153 129 Least tern 2 209 104 64 Royal tern 2 134 67 75 Black skimmer 3 142 47 63 14 Table 13. Waterbird nesting populations In Virginia, 1977. No. Total Mean Standard Species col onies breeding pairs colony size de' /iation Great blue heron 2 593 296 175 Green heron 5 21 4 4 Little blue heron 8 193 24 17 Cattle egret 7 486 69 31 Great egret 10 541 54 48 Snowy egret 13 2,844 219 192 Louisiana heron 12^ 722 66 58 Black-crowned night 12 1,737 145 262 heron Yellow-crowned night 4 18 4 1 heron Glossy ibis 12 536 45 37 White ibis 1 1 1 - Great black-backed 2 22 11 7 gull Herring gull 10 2,624 262 428 Laughing gull 28 31,197 1,114 1 ,108 Gul 1-bil led tern 2 105 52 53 Forster's tern 21 1,095 52 34 Common tern 22 3,556 162 176 Least tern 16 839 52 51 Royal tern 1 4,600 4,600 - Sandwich tern 1 5 5 - Caspian tern 1 1 1 - Black skimmer 19 2,687 141 153 Includes one colony site at which the species may breed but for which no estimate is available. L m % JwSj M '•ifiSt.-.- > o ] S II m CO r o eaje puejtaM ui)| Jsd sjjed Bujpaaiq '0|\| 16 Table 14. Rank order of 10 northeast States in waterbird nesting population size, wetland area , and coastline lenqth. Rank in Rank in Rank in Ran k in Rar ik in wa terbird seabird wader wetland coastline n umbers numbers numbers area ler igth^ only only (Km^) [Km) 1 VA VA NJ MJ (873) MD (3,088) 2 NJ NJ VA VA (798) MA (1,920) 3 m MA DE MD (744) VA (1,600) 4 NY NY MD DE (443) NY (677) 5 MD ME NY MA (181) RI (544) 6 KE MD MA NY (131) CT (432) 7 RI RI RI CT (47) NJ (368) 8 DE CT CT NH (15) DE (170) 9 CT OE ME RI (8) NH (26) 10 NH NH NH Data from Spinner 1969. Wetland area and coastline data not available for the southern section of Maine. 17 Table 15. Correlation measures between nesting waterbird b c numbers, wetland area , and coastline length in nine northeastern States (Maine excluded). Species Numbers vs. wetland area Correlation Numbers vs. coastline length All species All seabirds All wading birds Herring gull Common tern Least tern Black skimmer r r r r r r r 0.72* 0.67* 0.93** -0.1 0.43 0.63* 0.60 Snowy egret r = 0.85** Black-crowned night heron r = 0.47 r - 0. ,57 r = 0. ,60* r = 0. ,32 r = 0. ,57 r = 0. ,62* r = 0, ,45 r = 0, .20 r = 0. .33 r = 0, .75* All r values listed are from Spearman Rank tests, a non-parametric correlation method; * = P < 0.05, ** = P < 0.01. Wetland areas, in Km , from Spinner (1969). Coastal length in Km. Nesting occurred in only the five States from New York to Virginia. 18 with wetland area than is the density of seabirds which feed on land (gulls) and the pelagic zone in addition to marsh and bay areas. Nonetheless, water- birds as a group show significant correlations between numerical abundance and wetland area. Coastline length, used as another index of "coastal space", was poorly correlated with waterbird abundance (Table 15). Correlations of nesting abundance with wetland area and coastline were examined for six widely-distributed species of seabirds and wading birds (Table 15). An a^ posteriori prediction was that the abundance of the marsh- feeding species would show higher correlation with wetland area than the more "general ist" feeders. The expectation was only partly supported. Of the seabirds, only least terns showed a significant correlation between abundance and wetland area. This species is strictly an inshore-feeder, fishing mostly in inlets and marsh shallows (Erwin 1978). The other inshore-feeder, the black skimmer, did not show a significant correlation, although only five States were compared. Of the wading birds, snowy egret numbers were highly correlated with wetland area, but black-crowned night heron abundance only showed a correlation with coastline length. Snowy egrets seem to be more dependent upon marsh-dwelling aquatic organisms than black-crowns which prey upon birds, rodents, reptiles, etc. (Kushlan 1977). Similarly, Custer and Osborn (1977) found that the abundance of the three species which feed nearly exclusively in coastal salt marshes (great and snowy egrets, Louisiana herons) was significantly correlated with wetland area. The species which were less "specialized" or fed in fresh-water areas (black-crowns, cattle egrets, little blue herons) showed no correlation between abundance and wetland area per State. The herring gull showed the lowest correlation coefficient with wet- land area. The herring gull's omnivorous and refuse-feeding habits have probably emancipated it from a dependence upon food produced in coastal wetlands. To make the above comparisons more meaningful, it would be useful to have measures of nesting habitat availability and human disturbance. Although attempts to determine breeding habitat availability have been made (Burger and Lesser 1977), there is a problem in assessing "suitability" from a human as opposed to a bird perspective. "Wetland area" is a composite of feeding, nesting, and resting habitats and nesting abundance may be a complex function of these interdependent variables. The locations of major waterbird colonies along the northeast coast are shown on State coastal maps (Figures 2-10). These maps indicate waterbird "hot spots" and may provide impetus and direction for further research and for local and regional protection and management. Comparisons of mean colony sizes by States were made for several of the more widely-distributed species (Table 16). The mean colony size varies considerably for most species. Herring gulls nest in more widely-distributed, larger colonies in southern Maine, Massachusetts, and Rhode Island than in States from New Jersey south. However, this gull is still increasing south of New York and, in time, may show similar colony size distribution throughout its range. Common and least terns generally nest in many scattered colonies but, roseate terns nest at only a few locations. Therefore, local disturbance or environmental degradation could have a serious impact upon the roseate tern population as a whole. A species with many breeding populations, or demes, will be better buffered against extirpation than one which is confined to a few locations (Buckley and Buckley 1977). 19 Figure 2. Location of major nesting colonies in southern Maine and New Hampshire, 1977. Triangles indicate 300-1,000 pairs, circles > 1,000 pairs. 20 Figure 3. Location of major nesting colonies in Massachusetts, 1977. Triangles indicate 300-1,000 pairs, circles > 1,000 pairs. 21 Figure 4. Location of major nesting colonies in Rhode Island, 1977. Triangles indicate 300-1,000 pairs, circles > 1,000 pairs. 22 A ,u e o u E »^ o c 23 A > 3 24 Figure 7. Location of major nesting colonies in New Jersey, 1977. Triangles indicate 300-1,000 pairs, circles > 1,000 pairs. 25 Figure 8. Location of major nesting colonies in Delaware, 1977. Triangles indicate 300-1,000 pairs, circles > 1,000 pairs. 26 Figure 9. Location of major nesting colonies in Maryland, 1977. Triangles indicate 300-1,000 pairs, circles > 1,000 pairs. 27 Figure 10. Location of major nesting colonies in Virginia, 1977. Triangles indicate 300-1,000 pairs circles > 1,000 pairs. 28 T3 (U 4J o (U % (/) 14- 0 i/l Ol .' — ^ 4-> (/) 03 t. 4J •( — to fO Q. C s_ cn O) c +-> 'r— I/) +J « 00 (U OJ ^ C +-> *^_^ s_ 0 CD c ISJ *f— 0 l/l f— 1 >, 1 — 0 c u •■- c (/) TJ cu cn Ln CNJ >=i- C\J CM « — I ^ IJD 1 — 1 "^ ro «^ 00 Lf) 1 — 1 LO 0 ** 1— 1 . — 1 1 — 1 o o o v£> ro 00 O C3^ 1^ «^ 00 Ln r~^ ro 1 — 1 CM CO ro ro ^o 0 <0 ^ cr. 00 LO CM 0 LO 00 0 CM 0 • — t ro 1 — 1 CM 0 0 CO I— 1 cri .—1 I— ( 0 'a- en CM 1 — 1 1 — 1 CO 0 ro 0 CTl 1 — ( 00 ro "=d- C\l 0 ^ CM ^ « — 1 'S- CM 1 — 1 CM CO CM cr, ^f CO LO f- en CM LO C T3 0 r^ 0) s_ r^ ,— c -l-J c Ol r— 3 sz s_ OJ 2 3 cn S- CU c i_ 0 C7) (D ■M s- cn 1- 4-> cn ■»-> cu 1 cn c ■r— c ■^ >^ J>^ •r— •f— J= 0 n3 +-> 2 u c L. C7) E CU i/i 0 0.05). Although barrier island use by nesting seabirds is mucn higher (as expected) in Virginia where the ocean front is protected (Table 17), Long Island, New York ranks second in seabird use despite the fact that major stretches of beach are not protected. However, long-established colony sites of terns and skimmers are protected by signs on the south shore beaches of Long Island. Also, herring gulls have habituated to automobile traffic to such an extent that one of the largest colonies in the State occupies several loops of a parkway along Jones Beach. Wading birds use nesting habitat more similarly in the different States than do seabirds (Table 17). Even in New Jersey and New York, significant numbers (37% and 26%, respectively) nest on barrier islands. Perhaps because they nest in dense, inaccessible shrubs or trees away from bathing beaches, they are much less vulnerable to human intrusion than are seabirds which nest 30 o >, .-I S- o Oi en +-> +-> CO n3 s_ ■r- J^ -Q O cn O) •r- c: "o •<- S cn c ■o •.- ^-^ C v_-(4_ O ■o s« S- •r- 4-> JO c (T3 OJ a; to to Ol i. C7) Q. C ^ E 1/1 3 . I/) +-> QJ (D +J ■•-' n3 •r- 4-) (O 3r C O) . ■•-> 1— fO O) QJ ^ <— +-> (O o 1— c 03 +-> o cr o o Ol o 03 OJ CO CO ■ — V ro CM CM r— CM CD CM CM ■— CXD o cx> OJ O) S- <— ro >0 CM O r— <— OO c l/l 1- 1- ra ca to nc5 o c_> I — CM • — CM ^ CM "^ OO I — ^£> CSJ ro 00 CO OO CO I tn CM ro CTi CO 1 — CO CM I — CM CO r~~ CO CO LD CO CO CTl O cn o o o 1^ CX3 CM LD 00 f-^ "=* •* tn uo 'd- CTl CTl cr\ CO .— ■"^ •— CO (Tl CTl I — r^ OO 3: OO 3 c/i ■I-) (O •f-> OO ct t_> OO 3: OO : OO :^ ■»-> to s_ Ol s- q; OJ e -C c +-> IB 0) j:: CTl u o +-> •s to ■o (U 0) cn -o s- 3 fO ^ o c ^ • r— to S- 0) cu s- • r— IT3 CL r- -o ^^ ^— .,— o >+- to XJ to c IC x: u c 3 o l/l •r— 4J to • r— OJ OO s_ O 3 C1.4J CD (J "O 3 S- ,^ •(-> ro (O cn E "O OJ to s_ 0) ■o ■D 3 -E ^— ■!-> u O c CO »— t (T3 X3 31 Table 18. Recreational use along oceanfront beaches, Long Island, New York, to the eastern shore of Virginia. Percentages of total oceanfront are listed in parentheses, Length of oceanfront (in Km) Beaches under Bathing beaches - State vehicular restriction public and private Total New York^ 0 New Jersey 24 (13) Delaware 18 (46) Maryland 8 (16) Virginia 107 (79) .Either excluding all vehicles or limited to security or maintenance vehicles, South shore of Long Island only. 173 (100) 173 171 (90) 190 37 (96) 38 42 (84) 50 19 (14) 126 32 on overwashed, sandy beaches or dunes. In Virginia, with little disturbance on the beaches, wading birds and seabirds are equally abundant on barrier islands (Table 17). Also significant is the use of dredge material in New Jersey, Maryland, and Virginia. In most cases, dredge deposition material has been placed on marshes, making it difficult to determine if the dredge material per se or particular marshes provide the proximal cues in attracting nesting colonies. Records of colony location before dredging activities would help address this question. Dredge material deposited on low Spartina alterniflora marsh islands raises the elevation of the marsh and allows sub- sequent encroachment of woody vegetation (Soots and Parnell 1975). On those islands, there is little doubt that new heron nesting habitat becomes available. 33 METHODS OF ASSESSING BREEDING POPULATION SIZE A first requirement of most population studies is to obtain a precise count or an estimate of the number of organisms in the study area. This presents little difficulty when the organisms are large, sedentary, conspic- uous, diurnal, and live in homogeneous, open habitats. However, such conditions seldom hold for a given species. Waterbirds, in general, are relatively large and conspicuous, and are primarily diurnal except for night herons, petrels, and perhaps black skimmers. Their mobility while feeding and their tendency to nest in yery dense, patchy vegetation (e.g. herons, egrets) or in holes or crevices (petrels, guillemots), however, presents problems for censusing. In addition, the large size of many waterbird breeding colonies makes accurate estimating extremely difficult. The problems of locating and censusing waterbird colonies have been the subject of a number of publications (for example, Belopol'skii 1957,Kartaschew 1963, Kadlec and Drury 1968a, b, Drury 1973, Nisbet 1973, Drury 1974, Nettle- ship 1976, Buckley and Buckley 1976). In general, the most appropriate census methods will be dictated by the size of the geographic region to be surveyed, the species involved, the number of qualified personnel available, and funds available. At one extreme, censusing only a few colonies of cryptic-nesting species under conditions of limited support demands a ground count of nests; while, at the other extreme, a regional census with substantial funding would probably best be conducted using a combination of aerial censusing and photo- graphy with nest counts. A point which receives recurrent emphasis from experienced census workers is the need for replicability and standardization of procedures and reporting. For best results, censusing should be conducted (1) by the same individual (s) each year, (2) using the same, pre-tested tech- niques each time, (3) at comparable times (of day and of nesting phase). This should minimize the variance in the numbers estimated and allow more rigorous statistical evaluation of the "true" variance, i.e., the variability due to biological processes independent of sampling biases. Natural variation of adult numbers in a colony results from several sources. Feeding conditions vary during the day depending upon tide cycle, wind conditions, weather, etc., all of which influence the number of foraging birds (Dunn 1973, Nisbet 1973, Custer 1977). The stage of nesting also influences colony attendance. Incubation requires at least one adult at the nest at all times but, after hatching, both members of the pair may need to forage simultaneously to meet the demands of the brood. Other factors affect- ing numbers at a colony are distances between nesting and feeding grounds, the number of "surplus" (nonbreeding) adults in attendance (Kadlec and Drury 1968a), and disturbances by predators (Nisbet 1975, Robert and Ralph 1975). Because this study covered the entire northeastern U.S. coast, regional (large-scale) inventorying using rotary- and fixed-wing aircraft was employed in both 1976 and 1977. At selected colonies in each State, ground counts were made to provide a basis for assessing the accuracy of aerial data. Because conditions under which nest counts of the different species are taken vary so greatly, the accuracy of small-scale, "within-colony" sampling was tested in several colonies. These two levels of assessing census methods are treated separately below. 34 SAMPLING METHODS "WITHIN COLONY" When only a few colonies in an area require censusing, the researcher needs to know which of several methods to employ for a given species (or group) under certain habitat conditions. Usually the expense of aircraft will demand some type of ground method (boat or on foot). Of all ground methods, a total nest count using a marking method to prevent duplication is the most accurate. However, the accuracy of such "total" nest counts may be misleading (Drury 1973) unless a second count is made and a correction factor is applied, such as the Lincoln (mark-recapture) Index (Overton 1971). The accuracy of a one-search "total" count was compared to the "true-total" derived from a two-search count using the Lincoln Index (Table 19). Eight sample plots ranging from 0.06 to 1.10 ha were selected in various densities of vegetation in seven gull colonies. In each plot, all nests found on the first search were marked. A second search v/as then made, and a separate count of marked and unmarked nests was made. A qualitative assessment of nest dispersion (uniform, patchy) was also recorded. The error range of 4-22% is large considering the relatively small sample plots. Vegetation density rather than plot size seems to be the more impor- tant factor in determining error rates. The "1 ight"-vegetated plots had 4, 7, and 9% errors, while those in "moderate-dense" plots ranged from 7-22% (mean 15%). In summary, the accuracy of alleged "total" nest counts may be more apparent than real unless a second count is made, admittedly a \/ery time-con- suming process. However, the benefit one gains in achieving greater accuracy may be offset by causing greater disturbance, especially in large, dense colonies where several hours may be required to mark e^^ery nest. An alternative to a total nest count is a sample count, using the sample to derive a total population estimate. This approach is especially valuable where the habitat density or colony size renders a total count impractical. In general, two types of sampling schem.es may be employed in the field: plot (area) and plotless (distance) methods (Pielou 1969). Plot methods include quadrat, strip, or belt transect sampling, where (ideally) random "plots" are sampled and used to extrapolate the "true" population. Plotless methods com- monly used are nearest-neighbor distance (Clark and Evans 1954, Lloyd 1967), point-centered quarter, and line-intercept (Smith 1966). With these methods, distances are measured and converted to aerial measures. A disadvantage of all except the belt transect method is that the total colony areas to be censused must be calculated. Surveying or m.easuring from aerial photographs can be expensive and time-consuming. Both plot (belt transect) and plotless (point-centered quarter) methods were tested in gull and heron-egret colonies to test the efficacy of these sampling methods under different regimes of habitat and nest dispersion pattern (Appendix A). Gull and heron colonies were chosen because their size and inaccessibility (especially in the case of herons) often preclude total count methods. In the largest colonies, a large sample plot was used. Both sampling methods yielded highly variable population estimates, depending on vegetation and nest dispersion patterns (Table 20). 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