SHORT COMMUNICATIONS 783 Callitrichidae) numa ilha deflorestaAt&&a. Re- the role of infant-carrying in wild saddle-back vista Nordestina de Biologia 6: 105-l 37. tamarins (Sag&us ficicollis). Behav. Ecol. So- B~INSKI,S., AND P. E. Scorr. 1988. Association of ciobiol. 20:99-109. birds with monkeys in Costa Rica. Biotropica 20: IZAWA, K. 1978. A field study of the ecology and 136-143. behavior of the black-mantle tamarin (Suguinus BOINSKI,S., AND R. M. TIMM. 1985. Predation by nigricollis).Primates 19:241-274. squirrelmonkeys and double-toothedkites on tent- NEVILLE, M. K., K. E. GLAND~~,F. B~AZA,AND A. B. making bats. Am. J. Primatol. 9:121-128. RYLANDS. 1988. The howling monkeys, genus BROWN.L., AND D. AMAD~N. 1968. Eaales. hawks Alouatta, p. 349453. In R. A. Mittermeier, A. B. and falcons of the World. McGrawrHill, New Rylands, A. F. Coimbra-Filho, and G. A. Bou- York. chardet da Fonseca [eds.], Ecology and behavior DAWSON, G. A. 1976. 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Princeton Univ. sociationof Double-toothed Kites and white-faced Press, Princeton, NJ. capuchin monkeys. Auk 97:94-98. WILLIS, E. O., AND Y. ONIKI. 1978. Birds and army GOLDIZEN, A. W. 1987. Facultative polyandry and ants. Annu. Rev. Ecol. Syst. 91243-263. The Condor92783-788 0 The Cooper Ornithological Society 1990 SURVIVAL OF BREEDERS IN SANTA CRUZ ISLAND AND MAINLAND CALIFORNIA SCRUB JAY POPULATIONS’ JONATHAN L. A-IWCOD~ Manomet Bird Observatory,Box 936, Manomet, MA 02345 MARY Jo ELPERS U.S. Fish and Wildlife Service,Great Basin Complex, 4600 Kietzke Lane, Reno, NV 89502 CHAWS T. COLLINS Department of Biology, California State University,Long Beach, CA 90840 Key words: Scrub Jay; Aphelocoma coerulescens; den 1974, Atwood 1980b, Verbeek 1973) other as- cooperativebreeding; survivorship; Santa Cruz Island. pectsof their socialbehavior vary dramaticallybetween populations.The Florida ScrubJay, A. c. coerulescens, The Santa Cruz Island Scrub Jay (Aphelocomacoeru- has a well-developed system of cooperative breeding, lescensinsularis) is the most morphologically differ- in which groups of related birds defend year-round entiated member of the southern California Channel territories and nonbreedershelp raise offspringthat are Islands’ endemic avifauna (Johnson 1972). Further- not their own (Woolfenden and Fitzpatrick 1984). The more, its isolation from mainland Scrub Jay popula- principal factor associatedwith the evolution of this tions provides an opportunity to examine various fac- social system is the lack of suitable breeding space tors associated with the species’ social evolution within the population’s rare, patchy, oak scrubhabitat (Atwood 1980b, Woolfenden and Fitzpatrick 1984). (Woolfenden and Fitzpatrick 1984). All suitable hab- Although ScrubJays in generalare permanently mo- itat always seemsto be occupiedby establishedbreed- nogamousthroughout their breeding range (Woolfen- ers,which preventsyoung, subordinate individuals from acquiring nesting space. Consequently, breeding by l-year-old Florida ScrubJays is extremely rare (wool- fenden 1974,1975; Woolfenden and Fitzpatrick 1978, I Received 15 December 1989. Final acceptance17 1984). April 1990. In contrast,western mainland ScrubJay populations 784 SHORT COMMUNICATIONS TABLE 1. Annual survival rates of breeding Santa Cruz Island Scrub Jays (1975-l 985). Annual Annual YG5.W n Deaths mortality n Deaths mortality Mean survival 1975 9 0.00 7 1 0.14 0.938 1976 18 0.00 16 1 0.06 0.971 1977 19 :, 0.05 19 1 0.05 0.947 1978 19 0.00 19 1 0.05 0.971 1979 19 ; 0.05 21 1 0.05 0.950 1980 19 0.00 21 : 0.14 0.925 1981 23 2 0.09 28 0.11 0.902 1982 38 6 0.16 42 4 0.10 0.875 1983 40 1 0.03 42 1 0.02 0.976 1984 42 : 0.05 42 2 0.05 0.952 1985 36 0.08 35 6 0.17 0.873 Total 282 16 0.05 292 24 0.09 0.935 + 0.04 sBased on numberof individualspresent during indicated year that died priorto the followingbreeding season. Thus, of 23 malespresent in 1981, two (0.09) died prior to 1982. Seetext for furtherdiscussion. do not breed cooperatively (Pitelka 1951, Atwood habitat is saturatedis the frequencywith which young 1980b). Although few details have been publishedcon- individuals are able to acquire nesting territories. In cerning their socialbehavior or demography, the pres- relatively nonsaturated habitats, l-year-old breeders ence of yearling breeders in western mainland Scrub would be predicted to occur more frequently than in Jays has been documented by several investigators saturatedhabitats where suitable spaceis occupied by (Ritter 1972; Verbeek 1973; Elpers,unpubl. data), sug- established, older individuals. Data concerning this gestingthat in these populations suitable nesting hab- portion of our research will be presented elsewhere. itat frequently is available even to young individuals. Here we describeinformation concerninga secondim- Unlike the geographicallyand ecologically restricted portant and related aspect of Scrub Jay demography, Florida population, westernmainland ScrubJays occur namely, the frequencywith which establishedbreeders in a wide range of habitats throughout western North die, thereby creating vacancies in areas known to be America (Pitelka 1951). suitable nesting habitat. These resultsare summarized Like western mainland forms, Santa Cruz Island from studies of Scrub Jays on Santa Cruz Island (At- Scrub Jays also lack cooperative breeding (Atwood wood and Collins), the southern California mainland 1980b, 1980~).However, this subspeciesresembles the (Elpers),and Florida (Woolfendenand Fitzpatrick 1984, Florida Scrub Jay in that most first-year birds, as well unpubl. data). as some older individuals, fail to occupybreeding space and thereby attain reproductivestatus (Atwood 1980~). STUDY AREAS AND METHODS Nonbreeding Santa Cruz Island Scrub Jays do not re- Santa Cruz Island, located approximately 30 km from main on their natal territories and act as helpers, but the nearest mainland point, is the largest and topo- instead wander along the peripheriesof establishedter- graphically most diverse of the California Channel Is- ritories and in suboptimal habitatsuntil breedingspace lands, being approximately 249 km2 in area and rang- can be acquired (Atwood 1980~). ing elevationally from sealevel to 753 m (Power 1980). The demography of these populations in relation to It has been part of an island land mass since the early availability of breeding habitat is an important con- to mid-Pleistocene, althoughits degreeofisolation dur- sideration. One index of the extent to which breeding ing the lowered sea levels associatedwith glacial max- TABLE 2. Annual survival rates of breeding California mainland Scrub Jays (198 l-l 985). 1981 6 0 0.00 8 3 0.38 0.786 1982 19 3 0.16 19 4 0.21 0.816 1983 25 5 0.20 26 0.19 0.804 1984 4 0.13 30 : 0.10 0.885 1985 ::, 5 0.17 33 3 0.09 0.873 Total 111 17 0.13 116 18 0.19 0.833 + 0.04 ’ ’ Basedon number of individuals present during indicated year that died prior to the followingbreeding season. See text and legendto Table 1 for furtherdiscussion. SHORT COMMUNICATIONS 185 ima was less than at the present time (Vedder and Howell 1980, Wenner and Johnson 1980). The sub- stantialmorphological divergence exhibited by the Santa Cruz Island Scrub Jay, in which linear measurements and body weights average approximately 20% larger than those of the adjacent mainland population (Pi- telka 1951, Atwood 1980a), suggestsan extended pe- riod of genetic isolation. No evidence existsfor current interchange between the mainland and island Scrub Jay populations (Pitelka 1951, Jones 1975). Principal vegetation types in the Santa Cruz Island study area, located near the University of California’s Channel Islands Field Station, include (a) chaparral dominated by scrub oak (Quercusdumosa) and laurel 1 2 3 4 5 6 7 tl 9 10 11 sumac (MuZosmaluurina), (b) coast live oak (Quercus YEARSAl=fER FIRST OBSERVED BREEDING ugrifoliu)woodland, (c) variably open thickets of mule- fat (Bucchurisglundulosu), (d) introduced Eucalyptus FIGURE 1. Survivorshiprates of breedingScrub Jays groves,and (e) open grassland.Additional descriptions from three populations. Regressionlines are weighted of the study area are provided in Yeaton (1974) and by sample sizes contributing to each year’s survivor- Atwood (1980b). ship estimate. See text for further discussion. Mainland California Scrub Jays were studied at the Starr Ranch Wildlife Sanctuary of the National Au- dubon Society, located approximately 12 km northeast 0.531, n = 5). Data presented by Fitzpatrick et al. of San Juan Capistrano in the coastal foothills of the (1988) also failed to indicate differential rates of mor- SantaAna Mountains. The approximately279-ha study tality between breedingmale and