Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. ae + A J States Uspartment of Agriculture Forest Service Intermountain Research Station Research Paper INT-431 October 1990 ssessment of Nongame ird Habitat Using Forest urvey Data Renee A. O'Brien THE AUTHOR RENEE A. O’BRIEN is a range scientist in the Forest Survey Research Work Unit, Intermountain Research Station, Ogden, UT. She holds a B.S. degree in bot- any from Weber State College, Ogden, UT, and B.S. and M.S. degrees in range science from Utah State University, Logan. She began her professional career with the Forest Service in 1981 with the Intermountain Station. RESEARCH SUMMARY Forest Survey data have potential for use in obtain- ing information on the condition and diversity of the Nation’s forest resources relevant to wildlife habitat that is needed for planning and monitoring at State and regional levels. In this study, Forest Survey data were used to assess nongame bird habitat potential based on food and shelter requirements on 24 plots. These assessments were then evaluated using bird numbers. Results of the analyses showed some cor- relation of bird numbers with tree canopy variables, and iliustrate the potential for using Forest Survey data for wildlife habitat assessment, for identifying opportu- nities to improve habitat through management, and for predicting change in conditions over time. Assessment of Nongame Bird Habitat Using Forest Survey Data Renee A. O’Brien INTRODUCTION Recent environmental concern has generated much public pressure to protect and conserve the Nation’s renewable natural resources. Necessary for regionwide decisions is information on current resource conditions. Wildlife habitat is one resource of current interest that is an important element in forest planning and management decisions. Infor- mation on existing habitat conditions and predictive capabilities about future conditions on a regionwide scale is needed to allow evaluation of resource tradeoffs involved in management decisions. Forest inventory data may offer opportunity as an efficient way to streamline the task of wildlife resource monitoring. To meet the requirements for National assess- ments mandated by the Forest and Rangeland Re- newable Resources Planning Act of 1974 and other legislation, forest resource inventories are con- ducted on public and private lands by Forest Sur- vey, Forest Service, U.S. Department of Agriculture. Forest Survey projects are located throughout the continental United States and Alaska and are some of the most comprehensive, permanent plot invento- ries in the country. They provide permanent base- line data for most forested land, including most pri- vate, State, Bureau of Land Management of the U.S. Department of the Interior, and Indian lands; and excluding some National Forest lands in the West. The inventory procedures for the various Survey projects produce standardized timber statis- tics, with some regional differences in the scope and details of the inventories. The Forest Survey data base has the potential to provide information on forest conditions relevant to wildlife populations and on change in these condi- tions over time (O’Brien and Van Hooser 1983). At the regional level at which Forest Survey operates, some efforts have been made in the area of wildlife habitat assessment by Brooks (1986) in the North- east, Flather and others (1989) in the South, Ohmann (1983) in the Pacific Northwest, Rudis (1988) in the South, and Sheffield (1981) in the Southeast. This paper focuses on the ponderosa pine forests of Arizona. Forest Survey variables that could be useful for assessment of potential wildlife habitat are: Forest type Aspect Evidence of use Basal area Slope Distance to roads No. trees per acre Habitat type Fire history Site index Percent crown cover Logging history Quadratic mean Species composition Understory cover diameter Size of condition and height Stand-size class Vegetation Insect and disease Tree height concealment evidence Elevation THE PROBLEM Evaluating wildlife habitat is complex. Wildlife managers have made use of general timber stand variables such as forest type, stand-size class, age, canopy cover, and other stand features to predict potential wildlife use of a site for feeding, breeding, or resting. Specific habitat suitability models are being developed for predicting occurrence and quan- tifying value of potential habitat for some wildlife species. Most models are designed to provide site- specific comparisons and are not applicable to exten- sive forest inventory data. Forest Surveys operate at a much broader level than most research model- ing being done for wildlife habitat evaluation. This paper evaluates Forest Survey plot data for potential nongame bird habitat. General habitat criteria on food and shelter from the literature were used for habitat assessment. These habitat assess- ments were then evaluated using bird numbers col- lected on the same plots. The birds chosen for this study were secondary cavity-nesting foliage-gleaners and bark-gleaners (subsequently referred to as cavity-nesting glean- ers). These birds are important for several reasons. They are sensitive to timber management practices because they use old and dying trees for nesting (Balda 1969, 1975; Cunningham and others 1980; Diem and Zeveloff 1980; Medin 1985; Owens 1983; Sturman 1968; Szaro and Balda 1979) and because they forage in tree canopies. They are conspicuous, in many places common, and their diets consist of 75 to 90 percent insects (Bent 1946, 1948; Scott and Patton 1975), making them important for insect population control (Thomas and others 1979). Five species of cavity-nesting gleaners found in the study area are the pygmy nuthatch (Sitta pygmaea), white-breasted nuthatch (Sitta carolinensis), moun- tain chickadee (Parus gambeli), house wren (Troglo- dytes aedon), and brown creeper (Certhia ameri- cana). The main food and shelter variables chosen for evaluating cavity-nesting gleaner habitat are foliage volume and snag density. Foliage volume is impor- tant due to its relationship to the food supply. The relationship between gleaners and foliage volume is well documented by studies done in the coniferous forests of Arizona by Balda (1969) and Szaro and Balda (1979). Szaro and Balda (1979) reported that gleaners exhibited a positive correlation with in- creasing foliage volume across five study sites. Medin (1985) reported that among five recognized foraging guilds, gleaners were less numerous on logged plots where foliage volume had been reduced. Foliage volume also represents a number of impor- tant niche dimensions other than food quantity, including quality and quantity of perches, and shel- ter from weather and predators—all important characteristics for survival. For this study, snags were defined as standing dead trees greater than 1.2 m tall. Snag abundance is assumed to be related to the reproduction of cavity-nesters because they prefer these types of trees in which to excavate holes for nesting. Recom- mendations for snag size and densities in ponderosa pine forests are documented by Cunningham and others (1980). Snags are also preferred foraging strata for insectivorous birds (Szaro and Balda 1979). Balda (1975) found that snags were used intensively throughout the season relative to their availability. Kendeigh (1944) and Moore (1945) also provide evidence that snag use is not limited to the breeding season. For these reasons snags were in- cluded, even though this was not a breeding season study. Other habitat variables included in the study were woody understory cover and time since logging. STUDY AREAS This study was conducted at two locations in the ponderosa pine zone of the northwestern corner of Arizona, which is separated from the rest of the State by the Colorado River. The area is commonly referred to as the Arizona strip. Study area 1 was on the Kaibab Plateau and will subsequently be referred to as Kaibab. Study area 2, just south of Mount Trumbull, will be referred to as Trumbull. It is approximately 80 km southwest of Kaibab. The ponderosa pine zone occurs from 2,074 to 2,501 m elevation. Kaibab includes the Pinus ponderosa/ Poa longiligula community type and the Pinus ponderosa /Bouteloua gracilis habitat type (Hanks and others 1983). Kaibab is intensively managed for timber. All stands have been thinned to some extent, and the whole area is heavily used by hunt- ers and tourists. Trumbull includes only the Pinus ponderosa/Bouteloua gracilis habitat type. Plants common to both areas are Gambel oak (Quercus gambelii), New Mexican locust (Robinia neomexi- cana), cliffrose (Cowania stansburiana), mountain muhley (Muhlenbergia montana), blue grama (Bouteloua gracilis), and Indian ricegrass (Oryzopsis hymenoides). Trumbull is a more remote and less intensively managed area. There were greater con- trasts of forest conditions at Trumbull, including more thickets and more overstocked stands. There was a larger component of oak understory at Trum- bull than at Kaibab. METHODS The study was conducted in conjunction with the Forest Survey field inventory of Arizona. Twelve plots were sampled for bird numbers at each study area during July and August 1985. Included were actual Forest Survey plots and some supplemental plots added to provide a variety of tree height and canopy cover conditions in order to encompass a wide range of food availability. Five bird counting points approximately 120 m apart were established around each Forest Survey plot (fig. 1), in similar forest conditions. The area sampled for birds at each plot was roughly 6 ha. Birds were counted using the point sampling procedure recommended by Verner and Ritter (1985). Counts were made at each point on two separate days, within 1 hour of sunrise, based on the findings of Robbins (1981). Ten minutes were spent at each of the five points where the number and species of birds were de- tected and recorded. Detection and identification were based on sightings and calls. Two counts per point, five points per plot, and 12 plots per study area totaled 120 counts at each study area, fora total of 240 counts between Kaibab and Trumbull. Timber inventory variables were collected accord- ing to standard Intermountain Forest Survey inven- tory procedures (USDA FS 1985) by Forest Survey field crews. The Intermountain Forest Survey uses five variable-radius point samples to sample a 0.4- ha plot (fig. 1). Because points are sampled propor- tional to basal area, exact snag counts for a fixed area are unavailable. In addition to Forest Survey snag counts, every snag 10.2 cm diameter at breast height (d.b.h.) or larger within 60 m of each bird sampling point was recorded. The relationship between snag densities obtained with a BIRD PLOT CRAY FOREST SURVEY PLOT Figure 1—A representation of one study plot including Forest Survey plot and bird point configuration. variable-radius point sample compared to total fixed-area snag counts is the subject of a separate study and will not be addressed here. Forest Survey does not measure foliage volume directly. Crown volume was estimated from the Forest Survey data base using measurements of tree height, crown ratio, minimum and maximum crown widths, and crown shape. Foliage volume was then estimated by discounting the crown vol- ume estimates to bring them in line with other esti- mates reported in the literature for ponderosa pine forests (Cunningham and others 1980). These foli- age volume estimates represented the relative foli- age volume differences between the plots and made it possible to separate other tree foliage volume from ponderosa pine foliage volume. Cunningham and others (1980) found that bird use of foliage may be better explained if foliage volume is partitioned into ponderosa pine and other tree volume. Foliage volume was also estimated using an index of food availability developed by Schroeder (1983) as part of a Habitat Suitability Index (HSI) model for assessing potential habitat of the black-capped chickadee (Parus atricapillus)—another cavity- nesting gleaner species. This index is an assess- ment of food availability (the term “availability” was substituted for “suitability” in this paper) computed from a measure of average height of overstory trees and tree canopy closure. These variables are each assigned a rating, then combined in an equation (fig. 2) to arrive at an overall food availability rank- ing between 0 and 1.0. Food Availability Index = (CI * HI)" S = SAO'7, = o o ne} ao) £06 = 2 = — 0.5 — To) ro} sg & “5 0.4 = ” ” © 0.34 = ae a o Co2 SE g a ° ° e) 25 50 7S 100 Percent Cover Average Height of Overstory (m) Figure 2—Overall food availability index equation with individual cover and height indices (Schroeder 1983). Simple correlation and simple and multiple re- gression were used to analyze the relationships be- tween bird species numbers and the independent habitat variables: average height of tallest trees, crown canopy cover, snag density, foliage volume (ponderosa pine and other), the index of food availa- bility, woody understory vegetation cover, and time since logging. The Spearman test for correlation (SAS 1982) was used because it was assumed that the precision of bird counts was low and because the relationship between variables might not be linear. RESULTS The relationship between bird numbers and habi- tat variables varied depending on study area. Total numbers of the five species of cavity-nesting glean- ers were three times more abundant at Trumbull (199) as at Kaibab (65) for sites with similar foliage volume and snag density. There were more than six times the number of white-breasted nuthatches at Trumbull than at Kaibab. This supports one obser- vation made by Cunningham and others (1980) of a positive correlation between white-breasted nut- hatches and Gambel oak. No brown creepers were observed on any of the locations. Table 1 presents a summary of bird numbers and canopy-related habitat variables. Trumbull plots had slightly higher mean canopy cover and food availability, similar mean height and foliage vol- ume, and fewer snags than Kaibab plots. Spearman correlation coefficients (r) were com- puted between bird numbers and all habitat vari- ables for the two study areas separately and com- bined and are presented in table 2. Correlation coefficients between bird numbers and habitat Table 1—Summary of average number of birds and habitat variables per plot Average Ponderosa Other Number White Mountain Pygmy Crown height pine tree Woody snags Food Location breasted chicka- House nut- Total canopy tallest foliage foliage understory >10.2 availability number nuthatch dee wren hatch guild cover trees volume volume cover cm/ha index <3 oe eee eee -- Number --------------- Percent = ™m ------9nP/ha----- Percent Study area 1 (Kaibab) 01 1.0 0.5 0.5 0 2.0 51 28 60,864 0 9 1.3 1.00 02 1.0 5 ) 0 1.5 57 26 16,661 4,318 12 1.3 1.00 03 0) 0 0 3.5 3.5 37 27 59,519 0 0 3 84 04 5 25 0 0 3.0 21 29 36,641 0 0 aA 63 05 5 2.0 0 0 2.5 46 10 25,964 0 1 3 79 06 5 6.0 0 0 6.5 42 16 15,055 4,586 29 2 .89 07 0 0) 0 0 0) 35 22 35,289 1,229 24 5 84 08 1.5 5.5 0 0 7.0 16 13 11,495° 5,796 29 3 52 09 5 2.0 2.0 6.5 11.0 49 28 35,226 0 9 2.3 1.00 10 1.5 3.0 1.5 8.0 14.0 81 30 89,253 0 6 3.2 95 11 0 0 0 0 65 16 59,004 0 0 8 1.00 12 1.0 13.0 0 0 14.0 20 15 8,582 6,578 50 3 63 Mean Ao 2.9 3 1.5 5.4 43 22 37,796 1,876 14 1.0 84 Study area 2 (Trumbull) 13 0 6.5 0 6.5 13.0 23 21 34,425 0 11 0 71 14 6.5 10.0 0 3.5 20.0 54 21 34,650 7,272 35 3 1.00 15 45 10.5 0 9.5 24.5 54 21 63,079 1,445 1 2 1.00 16 5 3.0 0) 1.0 45 75 18 15,998 9,689 0 2 1.00 17 4.0 7.0 0) KS 18.5 58 14 60,232 4,529 6 0) 95 18 5.0 45 1.0 5.5 16.0 80 27 53,987 1,222 0 3 95 19 7.0 6.5 0) 14.5 28.0 48 26 64,622 9,137 11 15 1.00 20 4.5 Lo 0 10.5 22.5 50 23 37,752 4,358 17 1.2 1.00 21 0) 0 0 0) 0 5 13 8,408 0 14 3 .30 22 5 2.0 0 3.0 5.5 38 23 12,894 0 16 2 89 23 8.0 3.5 0 9.0 20.5 59 27 63,423 1,697 2 5 1.00 24 6.0 12.5 0 7.5 26.0 58 16 20,308 382 4 0 1.00 Mean 3.9 6.1 1 6.5 16.6 50 21 39,148 3,311 10 4 90 Table 2—Spearman correlation coefficients (1) for bird numbers compared with habitat variables; study areas separate and combined Average Ponderosa Other Number Crown height pine tree Woody snags Food canopy tallest foliage foliage understory >10.2 availability cover trees volume volume cover cm/ha index Percent M — -------- me/ha------- Percent Study area 1 (Kaibab) White—breasted nuthatch 0.03 0.07 -0.21 0.35 0.46 0.24 —0.13 Mountain chickadee —.37 -.18 —.56 53 56 —.29 —.48 House wren 51 .64 .48 -.46 —.08 174 53 Pygmy nuthatch 37 59 49 —.46 -.31 47 .28 Total birds —.23 ont —.23 .23 xyes —.06 —.32 Study area 2 (Trumbull) White-breasted nuthatch .46 56 170 .46 -.10 51 V3 Mountain chickadee BIW —.11 38 .22 .05 —.21 56 House wren .48 44 ens) -—.13 —.44 13 —.20 Pygmy nuthatch .06 42 182 .30 -.04 32 55 Total birds A5 31 76 32 -.01 .26 72 All locations White—breasted nuthatch .47 5 of 153 .07 .08 151 Mountain chickadee al -.23 .00 158 27 —.40 16 House wren OT. 158 34 —.36 -.18 48 .20 Pygmy nuthatch 44 .32 160 16 -.18 -.01 150 Total birds 31 .08 .34 45 .07 —.18 38 'P $0.01. variables produced some significant positive rela- tionships. Pygmy nuthatch exhibited significant positive correlations (r = 0.82 and 0.60) (P < 0.01) with ponderosa pine foliage volume at Trumbull and both study areas combined. House wren exhibited significant positive correlation with the average height of the tallest trees on both study areas com- bined (r = 0.58). White-breasted nuthatch exhibited a significant positive correlation with ponderosa pine volume at Trumbull (r = 0.70), as did the four species combined (r = 0.71). At all locations com- bined, white-breasted nuthatch and mountain chickadee had significant positive correlations (r = 0.53 and r = 0.58) with other tree volume, which included pinyon, juniper, and tree-form Gambel oak. Significant positive correlations were exhibited with the index of food availability by white-breasted nut- hatch at Trumbull and the combined study areas (r = 0.73 and r = 0.51), by pygmy nuthatch on the combined study areas (r = 0.50), and by the four species total at Trumbull (r = 0.72). These patterns, similar to what Diem and Zeveloff (1980) and Cunningham and others (1980) reported, were more evident at Trumbull or at all locations combined than at Kaibab. There was little correlation between bird numbers and snag densities, woody understory vegetation cover, or time since logging on either study area, except at Kaibab, where house wren had a signifi- cant positive correlation with snag density. Regres- sion analyses performed combining the habitat vari- ables yielded little improvement. DISCUSSION Results of this study illustrate the potential asso- ciated with using Forest Survey data for the assess- ment of wildlife habitat. Results of the analyses showed some correlation of bird numbers with the interrelated tree vanopy variables: total foliage vol- ume, ponderosa pine volume, other tree volume, and the index of food availability. These findings indi- cate that general foliage volume estimates or indices can be used to indicate relative habitat suitability. The food availability index is a good ordered vari- able (Spearman correlation test) and is sensitive to food availability reduction at high-canopy closure levels (fig. 2). This index of food availability is more easily obtained than foliage volume and appears to be as useful an indicator of food availability for gleaners. This study also illustrates the problems associated with using Forest Survey data for potential wildlife habitat assessment. One problem is in using vari- able-radius plots that sample trees proportional to basal area to get information on snags for wildlife. A study is under way to compare snag information obtained with variable-radius plots to actual snag counts. Habitat variables were tested by comparing differ- ences in bird use of different foliage volume and snag density conditions. However, differences due to study area overshadowed any differences within study area. The threefold increase in bird numbers from Kaibab to Trumbull can possibly be explained by the greater diversity, patchiness, and layering of the vegetation, the importance of which was re- ported by Langelier and Garton (1986). Reduced numbers of gleaners at Kaibab support the findings of Medin (1985) that gleaners are less numerous on logged plots where foliage volume has been reduced. The difference due to study area was observable but was difficult to detect using Forest Survey methodology, except that Trumbull plots had slightly higher mean canopy cover and food availa- bility than Kaibab plots. There are two possible reasons. First, a subset of Forest Survey plots were selected and supplemental plots were located to provide a wide range of foliage and snag conditions for this study, thus overriding the inherent differ- ences in the study areas. Second, analysis of addi- tional Forest Survey plot data indicated that both sites have similar percentages of plots on which evidence of logging, occurrence of thickets, and mul- tiple vegetation layers were reported. Forest Survey data are somewhat insensitive to subtle dif- ferences in vegetation structure and distribution, due to the general nature of the variables measured. The difference between areas was related to details of horizontal and vertical distribution of the vegeta- tion to which the birds were apparently more at- tuned but which would require much more detailed, time-consuming methodology to identify. There are problems with using animal numbers to assess habitat suitability. Van Horne (1983) reported that density may sometimes be a mislead- ing indicator of habitat quality. Density may reflect temporary or recent conditions rather than long- term conditions, social dominance may induce high densities in poor habitats, and censuses may be obtained in noncritical seasons. Diem and Zeveloff (1980) found that the movements of birds can reflect local perturbations that may be temporary re- sponses to short-term environmental factors and that are impossible to monitor. Therefore, high correlation should not be expected when comparing habitat suitability to bird numbers. Lack of a high degree of correlation between bird numbers and habitat variables does not mean that the other variables included in the study would not be useful indicators of wildlife habitat potential. Even though the value of snags was not demon- strated in this nonbreeding season study, the impor- tance of snags for cavity-nesting birds and other animals in general is well known (Thomas and others 1979). Recent publications emphasize snag management and Forest Service guidelines for retention of snags (Langelier and Garton 1986; Morrison and others 1986). A survey of snag densi- ties on other northern Arizona Forest Survey plots indicates that snag densities are rarely at recom- mended levels. None of the sites in this study con- tained recommended (Cunningham and others 1980) snag densities. Morrison and others (1986) concluded that current guidelines for large snag retention are appropriate, but even under snag management strategies, recommended densities are not being met. Although snag densities alone will probably not be a useful indicator of abundance of many bird species, general information on snags from statewide inventories would be useful for monitoring snag densities and, consequently, habi- tat potential, on all forest lands. SUMMARY Forest Survey projects throughout the country collect and maintain statewide multiresource data bases that may be useful for assessing and monitor- ing elements of wildlife habitat or trends over time in general forest conditions that have relevance for wildlife populations. One problem is that Forest Survey data are primarily collected to generate re- gional timber resource statistics, whereas most wildlife habitat research is done on a site-specific level. However, the State and regional level at which Forest Survey operates is also the level at which important information on the condition and diversity of the Nation’s resources must be moni- tored and at which program funding takes place. This study involving bird numbers illuminated some of the problems involved in habitat assess- ment. It also provided some evidence that Forest Survey data could be used as a starting point in identifying key issues or problem areas that need more site-specific studies. There is potential to use Forest Survey data to assess the capacity of the forests of an area to support insectivores or cavity- nesters and to identify opportunities to improve wildlife habitat through timber management. Inter- mountain Forest Survey is investigating other ways of monitoring change in forest conditions on a state- wide basis that could have relevance for wildlife and other forest resources. REFERENCES Balda, R. P. 1969. Foliage use by birds of the oak- juniper woodland and ponderosa pine forest in southeastern Arizona. Condor. 71: 399-412. Balda, R. P. 1975. The relationship of secondary cavity nesters to snag densities in western con- iferous forests. Wildl. Habitat Tech. Bull. 1. Albuquerque, NM: U.S. Department of Agricul- ture, Forest Service. 37 p. Bent, A. C. 1946. Life histories of North American jays, crows, and titmice. U.S. Natl. Mus. Bull. 191. Washington, DC: U.S. Government Printing Office. 495 p. Bent, A. C. 1948. Life histories of North American nuthatches, wrens, thrashers, and their allies. U.S. Natl. Mus. Bull. 195. Washington, DC: U.S. Government Printing Office. 475 p. Brooks, R. T. 1986. Forest Land Wildlife Habitat Resources of South-central Ohio. Resour. Bull. NE-94. Radnor, PA: U.S. Department of Agricul- ture, Forest Service, Northeastern Forest Experi- ment Station. 32 p. Cunningham, J. B.; Balda, R. P.; Gaud, W. S. 1980. Selection and use of snags by secondary cavity- nesting birds of the ponderosa pine forest. Res. Pap. RM-222. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 15 p. Diem, K. L.; Zeveloff, S. I. 1980. Ponderosa pine bird communities. In: Proceedings of a workshop for management of western forests and grasslands for non-game birds. Gen. Tech. Rep. INT-86. Ogden, UT: U.S. Department of Agriculture, Forest Serv- ice, Intermountain Forest and Range Experiment Station: 170-197. Flather, C. H.; Hoekstra, T. W.; Chalk, D. E.; Cost, N. D.; Rudis, V. A. 1989. Recent historical and projected regional trends of white-tailed deer and wild turkey in the southern United States. Gen. Tech. Rep. RM-172. Fort Collins, CO: U.S. Depart- ment of Agriculture, Forest Service, Rocky Moun- tain Forest and Range Experiment Station. 22 p. Hanks, J. P.; Fitzhugh, E. L.; Hanks, S. R. 1983. A habitat type classification system for ponderosa pine forests of northern Arizona. Gen. Tech. Rep. RM-97. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain For- est and Range Experiment Station. 22 p. Kendeigh, S. C. 1944. Measurement of bird popula- tions. Ecological Monographs. 14: 67-106. Langelier, L. A.; Garton, E. O. 1986. Management guidelines for increasing populations of birds that feed on western spruce budworm. Agric. Handb. 653. Washington, DC: U.S. Department of Agri- culture, Forest Service. 19 p. Medin, D. E. 1985. Breeding bird response to diameter-cut logging in west-central Idaho. Res. Pap. INT-355. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Re- search Station. 12 p. Moore, A. D. 1945. Winter night habitats of birds. Wilson Bulletin. 57: 253-260. Morrison, M. L.; Dedon, M. F.; Raphael, M. G.; Yoder-Williams, M. P. 1986. Snag requirements of cavity-nesting birds: are USDA Forest Service guidelines being met? Western Journal of Applied Forestry. 1: 38-40. O’Brien, R.; Van Hooser, D. D. 1983. Understory vegetation inventory: an efficient procedure. Res. Pap. INT-323. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 6 p. Ohmann, Janet L. 1983. Evaluating wildlife habitat as part of a continuing, extensive inventory. In: Bell, J. F.; Atterbury, Toby, eds. Renewable re- source inventories for monitoring changes and trends: proceedings of an international conference. Corvallis, OR: Oregon State University: 623-627. Owens, G. C. 1983. Nest site partitioning of secon- dary hole-nesting birds in oak woodland. Fullerton, CA: California State University. 58 p. Thesis. Robbins, C. S. 1981. Effect of time of day on bird activity. Studies in Avian Biology. 6: 275-286. Rudis, V. A. 1988. Nontimber values of Louisiana’s timberland. Resour. Bull. SO-132. New Orleans, LA: U.S. Department of Agriculture, Forest Serv- ice, Southern Forest Experiment Station. 27 p. SAS. 1982. SAS user's guide: statistics. 1982 ed. Cary, NC: SAS Institute Inc. 584 p. Schroeder, R. L. 1983. Habitat suitability index models: Black-capped chickadee. FWS/OBS-82/ 10.37. Washington, DC: U.S. Department of the Interior, Fish and Wildlife Service. 12 p. Scott, V. E.; Patton, D. R. 1975. Cavity-nesting birds of Arizona and New Mexico Forests. Gen. Tech. Rep. RM-10. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain For- est and Range Experiment Station. 52 p. Sheffield, R. M. 1981. Multiresource inventories: techniques for evaluating nongame bird habitat. Res. Pap. SE-218. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern For- est Experiment Station. 28 p. Sturman, W. A. 1968. The foraging ecology of Parus atricapillus and P. rufescens in the breeding sea- son, with comparisons with other species of Parus. Condor. 70: 309-322. Szaro, R. C.; Balda, R. P. 1979. Bird community dynamics in a ponderosa pine forest. Studies in Avian Biology. 3: 1-66. Thomas, J. W.; Anderson, R. G.; Moser, C.; Bull, E. L. 1979. Snags. In: Thomas, J. W., ed. Wildlife habitats in managed forests: The Blue Mountains of Oregon and Washington. Agric. Handb. 553. Washington, DC: U.S. Department of Agriculture: 60-77. U.S. Department of Agriculture, Forest Service. 1985. Arizona Forest Survey field procedures 1985. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 2 parts. Van Horne, B. 1983. Density as a misleading indica- tor of habitat quality. Journal of Wildlife Man- agement. 47: 893-901. Verner, J.; Ritter, L. V. 1985. A comparison of transects and point counts in oak-pine woodlands of California. Condor. 87: 47-68. O’Brien, Renee A. 1990. Assessment of nongame bird habitat using Forest Survey data. Res. Pap. INT-431. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 8 p. Forest Survey data were used to assess nongame bird habitat potential based on food and shelter requirements on 24 plots. These assessments were then evaluated using bird numbers. Results of the analyses showed some correlation of bird numbers with tree canopy variables, and illustrate the potential for using Forest Survey data for wildlife habitat assessment. KEYWORDS: foliage volume, forest inventory, wildlife habitat assessment INTERMOUNTAIN RESEARCH STATION The Intermountain Research Station provides scientific knowledge and technology to im- prove management, protection, and use of the forests and rangelands of the Intermountain West. Research is designed to meet the needs of National Forest managers, Federal and State agencies, industry, academic institutions, public and private organizations, and individu- als. Results of research are made available through publications, symposia, workshops, training sessions, and personal contacts. The Intermountain Research Station territory includes Montana, Idaho, Utah, Nevada, and western Wyoming. Eighty-five percent of the lands in the Station area, about 231 million acres, are classified as forest or rangeland. They include grasslands, deserts, shrublands, alpine areas, and forests. 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