HARVARD UNIVERSITY Library of the Museum of Comparative Zoology '^US. COMP. 200L OCCASIONAL PAPERS I irrary «f ^^^ NOV 1 5 1984 MUSEUM OF NATURAL HISTORY The University of Kansas -nivhr^TV Lawrence, Kansas NUMBER 114, PAGES 1-8 26 OCTOBER 1984 REPRODUCTIVE ECOLOGY OF THE FERAL PIGEON, COLUMBA LI VIA By Richard F. Johnston' The Rock Dove, Columba livia, was domesticated around 5,000 years ago (Sossinka, 1982), and since that time escapees from captivity have been colonizing suitable places as feral populations. These birds have the capability of successfully joining truly wild populations of Rock Doves (Murton and Clarke, 1968), but most often they form colonies in or near human activities in cities or in the countryside. Feral pigeons do not need human help in living, but they often exploit human architecture and agriculture. Additionally, feral pigeons preserve a number of features that were imposed upon captive pigeons by artificial selection by humans; chief among these is year-round breeding schedules. Wild Rock Doves have a "photoperiodic" breeding season of around 8 months' duration, but feral pigeon populations tend to show a 12-month schedule (Murton, Thearle, and Coombs, 1974). In eastern Kansas, feral pigeons were long assumed to have a 12-month breeding schedule (Johnston, 1964), but details have been lacking. As a result of a research program on feral pigeons, designed to evaluate the significance of year-round breeding, descriptive data on length of the breeding season and ancillary matters of natural history were gathered on the feral pigeons at the University of Kansas in 1983. Materials and Methods The study population resides on the outer faces of the Museum of Natural History (Dyche Hall) at the University of Kansas. The number of pigeons in that part of the campus ranges from around 60 to as many as 137. of which only some actually pair, nest, and rear young. The birds could form as many as 42 pairs in the places under observation, but sometimes only half that number is present. ' Museum of Natural History and Department of Systematics and Ecology, The University of Kansas, Lawrence, Kansas 66045. 2 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY Adults were trapped and color-banded for future identification. Young were weighed and banded at age 18 days. Breeding adults and young were scored for plumage color and pattern. All phases of the reproductive cycle for all known pairs were monitored for the year. Frequencies of plumage phenotypes of non-breeding and loafing birds were determined by counts made of the birds resting on the roof of Spooner Hall, across from the study center at Dyche Hall. A 20x telescope was used and individuals were scored into 5 categories of plumage color and pattern (cf. Cole, 1969; Dunmore, 1968). Results Pair formation. — The general behavior of pair formation and mainte- nance of the pair bond was normal for feral pigeons (e.g.. Whitman, 1919; Levi, 1974; Burley, 1981), with one exception. The birds at Lawrence tended to choose partners of unlike plumage color and pattern— that is, they paired negatively assortatively by plumage (Table 1). Plumages of feral pigeons can be described as follows (cf. Goodwin, 1983): (a) blue bar (the plumage of wild Rock Doves — gray mantle with two dark wing bars), (b) checker (a checked mantle of little, moderate, or heavy melanin in the coverts), (c) T-pattern (a dark mantle with small gray marks), (d) spread (an overall melanic plumage), and (e) other (albinos, reds, and, poten- tially, dozens of others). As the data show, the feral pigeons at Lawrence tended to mate with birds of unlike plumage, a significant tendency when tested against the possibility that the birds consorted randomly with respect to plumage. Breeding season. — Some nesting activity was found to occur in every month of 1983 (Fig. 1). The peak of activity was from late spring through early autumn; the first nest with eggs was completed in mid-January, and the last in early December. Adult birds maintained normal schedules of incubation and brooding at all times of the year. This means that females sat by night and males by day; some birds occasionally had to endure direct exposure to rain, ice, and snow. Temperatures as low as -20°F occurred in December. Rates of hatching and fledging. — Information on hatching and fledging rates is presented in Table 2, in which both the total sample of eggs and Table 1. Observed and expected pairing in feral pigeons, Lawrence, Kansas, 1983. Homologous Pairs* Heterologous Pairs** Observed Expected 2 10.98 35 26.02 Chi-square = = 10.44 (/' = 0.005) *bluebar X bluebar: checker x checker; TxT; spread x spread; other x other. **the remaining ten non-homologous pairings. REPRODUCTIVE ECOLOGY OF THE FERAL PIGEON 20 n CZ CD ^ 10 0 — I — I — I — I — I — I — I — I — I — I — I — J FMAMJ JASOND MONTH Figure L— Histogram depicting frequency of initiation of nests by feral pigeons, Lawrence, Kansas, 1983; N = 74. that only for the fall and winter are presented. The rate of hatching in the spring and summer was unusually low, and as a result the rate for the year was only 48.6 per cent. The rate for the winter months was considerably higher, at 60.5 per cent. Fledging rates of both samples were nearly the same— about a third of all eggs laid gave rise to young that left the nest. This does not mean that fall and winter breeding was necessarily favorable for pigeons, because most of the winter fledging occurred in October. October of 1983 was an extremely mild period climatically, unlike the late autumn of many years. Moreover, fledging rate as a function of hatched eggs was considerably less in the winter sample than in the summer. Variation in plumage phenotypes. — Nineteen samples of the frequen- cies of the common plumage phenotypes were secured in the period March Table 2. Rates of hatching and fledging for feral pigeons at Lawrence, Kansas, 1983. Sample ,V 7c of eggs % of eggs hatching All nests Eggs 140 100 Hatching 68 48.6 Fledging 45 32.1 66.2 Nests Jan. Feb. Oct-Dec Eggs 38 100 — Hatching 23 60.5 — Fledging 12 31.6 52.2 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY to November. The data were of crude counts of birds resting at various times of day on the south-facing roof of Spooner Hall; a summary is presented in Table 3. A temporal change in frequencies was detectable through the year. By November, fewer blue bar and T-pattern birds, and more checker and spread, occurred, relative to March. The frequencies differed significantly, March-April to November, largely due to the winter increase in the frequency of the spread phenotype. Survival of individuals from date of laying is summarized in Figure 2, which shows a twofold difference, summer over winter. 100 f> 90 80 70 CD Q. E 60 03 OO ■ 1 O 50 c CD o ^_ 40 CD Q_ 30 20 - 10 - — CX) o o - v •• o •^ ••• (III) OQDO *\m ^K ^^^A A A ■••••• (IIIIT) ODODQCCD O B rmoTTiff^ 1 1 1 1 1 1 1 0 0 10 20 30 40 50 60 70 Age in days Figure 2.— Plot depicting survivorship curves of feral pigeons, Lawrence, Kansas, 1983. A: nests begun February to September; B: nests begun October to December. REPRODUCTIVE ECOLOGY OF THE FERAL PIGEON 5 Table 3. Plumage phenotypes of adult pigeons at Lawrence, Kansas, March through November, 1983. Plumages Date Blue Bar Checker T Spread Other March, April N 104 51 81 2 10 Frequency 42% 20% 32% 1% 4% August-September N 51 27 47 6 7 Frequency 37% 20% 34% 4% 5% November N 159 109 124 27 19 Frequency 36% 25% 28% 6% 4% Chi-square= 14.37 (p< .01) Discussion Assortative mating.— h. pattern of negative assortative mating by plumage also was found in the feral pigeons of Manchester, England by Murton, Westwood, and Thearle (1973). Their sample was six times the size of that for Lawrence, and the conclusion of negative assortative pairing seems as solid as possible from these data sets. Nevertheless, Obukhova and Kreslavskii (1982) found positive assortative patterning in two of three samples of feral pigeons from the western U.S.S.R. All three samples were unusual in apparently lacking checkered phenotypes. Like- wise, Mainardi (1964) also found positive assortment of pairing in Italian feral pigeons. At present there is no means to resolve the observed discrepancies, so it appears that feral pigeons show variation in mate choice by plumage color and pattern. It is important to know that feral pigeons at Lawrence show this pattern, for it is rare in animals generally. Negative assortative mate choice will tend to increase genie heterozygosity, at least for color and pattern genetic loci, but probably also for other polymorphic loci. A high level of genie heterozygosity may be advantageous in promoting develop- mental canalization (Mitton, 1984), and this could be a part of the winter breeding capability. Breeding season. —Tht year-round breeding schedule at Lawrence is paralleled by those of pigeons at Flamborough Head, in what was formerly Yorkshire, England (Murton and Clarke, 1968) and Manchester, England (Murton, Thearle, and Thompson, 1972), and for Narragansett Bay, Rhode Island, U.S.A. (Preble and Heppner, 1981). No two schedules are precisely the same, showing what may be local responses to environmental (largely climatic?) variation. But, all schedules agree in having a signifi- cant proportion of nesting attempts in winter. Although feral pigeons are capable of successfully rearing young in the OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY severest winter weather at Lawrence, Kansas, it is not clear what part of the population is responsible for this. Since the costs of wintertime reproduction are likely to be considerable, individuals breeding then can be expected to show effects of such an adjustment. This has not as yet been identified. Conceivably, it could involve a tradeoff of possible reproduc- tion for reduced longevity (Roughgarden, 1979). The English birds have been thought (Murton, Westwood and Thearle, 1973) to separate into long-season versus photoperiodic season breeders by plumage phenotype— more melanic birds bred through the winter seasons, and most blue bar and checker birds showed a shorter, pho- toperiodic schedule. Not all the plumages of birds breeding at Lawrence in 1983 were ascertained, so it is not possible to say anything about plumages of summer versus winter breeders— certainly not about the frequencies at which the different phenotypes breed. However, data on plumages of nestlings (Table 4) show a larger proportion of blue bar plumages in summer, and lesser in winter, which suggests that the parental birds for the .two seasons were themselves significantly different in plumages. The genetic basis of plumage color and pattern is known for feral pigeons (Horlacher, 1930; Hollander, 1938). At Lawrence, it is likely that a larger sample of nestlings will support the idea that birds approaching the wild phenotype of Rock Doves (blue bar plumage) tend to breed in the spring, summer, and fall, and that birds not approaching the wild phenotype (those tending toward some degree of melanism) form a disproportionately large fraction of the breeders in winter. The possible reproductive advantages of melanic plumages in feral pigeons have generated considerable speculation (Murton, Thearle. and Coombs, 1974; Dunmore, 1968; Cole, 1969). Dark plumages may have some thermoregulatory advantages in winter (Hamilton and Heppner, 1967), but, as Walsberg, Campbell, and King (1978) have shown, under certain circumstances these advantages can also be realized by pigeons in fully albino plumage. Table 4. Plumage phenotypes of 18-day nestlings of feral pigeons at Lawrence. Kansas. Plumage Phenotype Sample Blue Bar Checker T Other Sum March-September, 1983 N Per cent 16 61.6 7 27.0 3 11.6 0 0 26 i 100 October-December, 1983 N Per cent 6 30.0 7 35.0 7 35.0 0 0 20 100 Chi-square = 5.61 (.05 > p<.l) REPRODUCTIVE ECOLOGY OF THE FERAL PIGEON 7 Variation in plumages. —Frequencies of the common plumage colors and patterns were found to vary over a period of 4 years at Manchester. England (Murton, Thearle, and Coombs, 1974). The variation noted at Lawrence (Table 3) is therefore not exceptional. The direction of the trend, from high blue bar and low spread frequencies toward the reverse, is not exceptional either, if indeed it proves true that the melanic plumages are disproportionately added to the population in winter (as suggested by the data in Table 4). Hatching and fledging rates. — In the overall sample, the Lawrence pigeons had a low hatching per cent compared to birds studied by Murton and Clarke (1968) and Preble and Heppner (1981)— just 49% as compared to 61%— 70% for the former and 56%-58% for the latter. Fledging rate per eggs laid was likewise lower— just 32 % versus 43 % -49 % (Murton and Clarke, 1968) and 42%-48% (Preble and Happner, 1981). The figures for Lawrence are heavily influenced by the poor hatching rate in the late spring and the low fledging rate for the winter breeding birds. Predation was low in the Lawrence population— three nestling birds were killed and eaten by unknown predators in the spring. Predators known to use the outside of the 7th floor of Dyche Hall at least occasionally in the last five years are the raccoon (Procyon lotor), screech owl Otiis asio), and great horned owl (Bubo virginianus). Clues at the scenes of predatory events included loose feathers and drops of blood, consistent with the actions of any of these three possible predators. Other likely causes of death to eggs and young are mostly climatic, and mostly in the winter— low temperatures and snow cover. Growth rates of young were low in November and December, a consequence partly to the difficulty parents had in finding food enough for themselves and their young, and partly to diverting bodily reserves from growth to ther- moregulation. The weather was the coldest ever recorded at Lawrence in December; it was also one of the snowiest Decembers, and the duration of snowcover was on the order of 2.5 weeks in most parts of town. Adults were sufficiently food-stressed that they resorted to eating overwintering buds of elms (Ulmus americanus); this was done with great difficulties in perching in the trees and was rewarded with relatively low nutrition, compared with seeds. LITERATURE CITED BuRLEY. N. 198L Mate choice by multiple criteria in a monogamous species. Amer. Natur., 117:515-528. Cole. G. 1969. Plumage colors and patterns in the feral rock pigeons of central Arizona. Amer. Midi. Natur., 82:613-618. DuNMORE, R. 1968. Plumage polymorphism in a feral population of the rock pigeon. Amer. Midi. Natur.. 79:1-7. Goodwin, D. 1983. Pigeons and Doves of The World. Cornell Univ. Press, Ithaca, N.Y. 3rd Ed., 363pp. Hamilton. W.. Ill and F. Heppner. 1967. Radiant solar energy and the function of black homoiotherm pigmentation: an hypothesis. Science. 155:196-197. Hollander, W. 1938. Inheritance of certain "blue-black"" patterns and "bleached" coloration in the domestic pigeon. Genetics, 23:12-23. 8 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY HoRLACHER, W. 1930. Studies on inheritance in pigeons VII. Inheritance of red and blaci patterns in pigeons. Genetics, 15:312-346. Johnston. R. 1964. The breeding birds of Kan.sas. Univ. Kansas Pub). Mus. Nat. Hist., 12:575-655. Levi, W. 1974. Tlie Pigeon. Levi. Sumter, S.C. Mainardi, D. 1964. Effetto evolutivo della selezione sessuale basata su imprinting in Columba livia. Revist. Itai. Ornith., 34:213-234. MiTTON, J. 1984. Relationships between protein heterozygosity, developmental stability, and growth rate. Ann. Rev. Ecoi. Syst., 15: in press. MuRTON, R. and S. Clarke. 1968. Breeding biology of rock doves. British Birds, 61:429-448. Murton, R., R. Thearle, and C. Coombs. 1974. Ecological studies of the feral pigeon Columba livia var. III. Reproduction and plumage polymorphism. J. Appl. Ecol., 11:841-854. Murton, R., R. Thearle, and J. Thompson. 1972. Ecological studies of the feral pigeon Columba livia var. I. Population, breeding biology and methods of control. J. Appl. Ecol., 9:835-874. Murton, R., N. Westwood, and R. Thearle. 1973. Polymorphism and the evolution of continuous breeding season in the pigeon Columba livia. J. Reprod. Pert. Suppl. 19:561-575. Obukhova, N. Yu and A. G. Kreslavskii. 1982. Structure of crosses in populations of rock doves Columba livia. Zool. Zh., 61:461-464. Preble, D. and F. Heppner. 1981. Breeding success in an isolated population of rock doves. Wilson Bull., 93:357-362. Roughgarden, J. 1079. Tlicon- of Population Genetics and Evolutionary Ecology: An Introduction. Macmillan, N.Y. Walsberg, G., G. Campbell, and J. King. 1978. Animal coat color and radiative heat gain: a re-evaluation. J. Comp. Physiol. B. 126:211-222. Whitman. C. 1919. Tlie Postlmmou.s Works of C. O. WJntman. Ed. H. A. Carr. Washington. D.C. I University of Kansas Publications MUSEUM OF NATURAL HISTORY The University of Kansas Publications, Museum of Natural History, beginning with volume 1 in 1946. was discontinued with volume 20 in 1971 . Shorter research papers formerly published in the above series are now published as Occasional Papers. Museum of Natural History. The Miscellaneous Publications, Museum of Natural History, began with number 1 in 1946. Longer research papers are published in that series. Monographs of the Museum of Natural History were initiated in 1970. All manuscripts are subject to critical review by intra- and extramural specialists; final acceptance is at the discretion of the publications committee. Institutional libraries interested in exchanging publications may obtain the Occasional Papers and Miscellaneous Publications by addressing the Exchange Librarian, The University of Kansas Li- brary, Lawrence, Kansas 66045. Individuals may purchase separate numbers of all series. Prices may be obtained upon request addressed to Publications Secretary, Museum of Natural History, The Univer- sity of Kansas, Lawrence, Kansas 66045. Editor: E. O. Wiley Managing Editor: Joseph T. Collins PRINTED BY UNIVERSITY OF KANSAS PRINTING SERVICE LAWRENCE, KANSAS 7 0 7 0 \\h i>^ 3 2044 093 361 699 DATE DUE ADD 1 ^ -OADit HI"4tU. 0 Zuu4 OEMCO, INC. 38-2931