Scrub lay. Body weights. of the Santa Cruz Island. Page 148 North American Bird Bander Vol. 4, No. 4

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1 Bdy weights f the Santa Cruz Island Scrub lay Jnathan L. Atwd The highly distinctive Santa Cruz Island Scrub Jay, Aphelcma cerulescens insularis, is entirely restricted in its gegraphic distributin t Santa Cruz Island, Santa Barbara Cunty, Califrnia. Lcated apprximately 18 miles frm the nearest mainland pint, Santa Cruz Island has prbably been separated by at least a narrw water barrier frm the suthern Califrnia mainland since at least early--mid Pleistcene times (Wenner and Jhnsn, in press}. Althugh the histry f A. cerulescens n Santa Cruz Island is uncertain (Atwd, 1978), the rather prnunced mrphlgical differentiatin f insularis frm mainland Scrub Jay frms suggests a cnsiderable perid f genetic as well as gegraphic islatin fr the island ppulatin (Jhnsn, 1972). Differentiatin f insularis has ccurred primarily in the characteristics f size and plumage clratin. Pitelka (1951) fund that bill length f the Santa Cruz Island Scrub lay averaged 20.7% larger than that f the adjacent mainland subspecies, A. c. califrnica, with similar size increases being fund in measurements f wing, tail, and tarsus. In plumage characteristics, insularis is much darker than califrnica, with mre intensely blue clratin being fund in the island ppulatin (Pitelka, 1951). The selective factrs respnsible fr the Santa Cruz Island Scrub Jay's plumage differentiatin appear unclear at present (Atwd, 1978); hwever, the subspecies' size differentiatin is likely due t an eclgical shift resulting frm the depauperate insular avifauna (Pitelka, 1951; Yeatn, 1974). Thrugh mrphlgical cmparisns f the Santa Cruz Island Scrub Jay with mainland iay ppulatins were presented by Pitelka (1951). Only recently, hwever, have lng-term field studies f insularis prvided specific data n the breeding bilgy and scial behavir f the subspecies (Atwd, 1978). In cnjunctin with these nging behaviral studies f the Santa Cruz Island Scrub Jay, cnsiderable bdy weight data were btained and are summarized here. Methds A ttal f 248 Santa Cruz Island Scrub Jays were marked with unique clr band cmbinatins between January 1975 and Nvember Eleven f these individuals were banded as nestlings; the remainder were captured using simple wire mesh grund traps baited with peanuts and sunflwer seeds. Captured birds were aged accrding t the criteria established by Pitelka (1945); especially useful were the characteristics f clr and shape f the greater primary cverts and shape f the rectrices. While actively breeding females culd be sexed by the presence f a brd patch, the clacal prtuberance f knwn breeding males was s slight as t render this character useless in sex identificatin. Therefre, the sex f mst individuals was determined by the behavir f pairs at nests and by sexual differences in vcalizatins (Atwd, 1978; Barbur, 1977). Bdy weights were measured t the nearest gram with a 300-gram Pesla balance calibrated in 2-gram increments. Results and discussin Published data n the bdy weights f the Santa Cruz Island Scrub Jay are limited t a sample f 37 (20 males, 17 females) prvided by Pitelka (1951). Substantial amunts f live bdy weight data were btained in the present study, and prvide new infrmatin cncerning 1) physilgical effects n this species f capturing and handling, 2) sexual dimrphism in bdy weight, and 3) seasnal variatin in bdy weight. Weight data frm 25 individual Santa Cruz Island Scrub Jays which were recaptured within tw days f a previus capture are available in 29 instances. Of these clsely spaced recaptures, 52% shwed a decrease in weight (mean decrease = 4% f initial bdy weight), 27% increased in weight (mean increase = 2% f initial bdy weight), and 21% experienced n weight change. Althugh these data are t limited t permit a rigrus statistical analysis, there appears t be a general trend f Page 148 Nrth American Bird Bander Vl. 4, N. 4

Table 1. Bdy weights f selected U.S. subspecies ef _Aphelcma cerulescens. Bdy Weight (mean(range, sample size)) Subspecies Distributin Males Females califrnica' castal central Califrnia 94.

2 Table 1. Bdy weights f selected U.S. subspecies ef _Aphelcma cerulescens. Bdy Weight (mean(range, sample size)) Subspecies Distributin Males Females califrnica' castal central Califrnia 94.2 (84-107, n-29) 85.5 (80-93, n-18) cleptica San Francisc Bay regin, Califrnia (90-112, n-14) 96.0 (80-107, n-11) caurina' castal nrthern Califrnia 98.4 (87-111, n-29) 87.7 (80-97, n-9) bscura' castal suthern Califrnia 78.6 (70-93, n-57) 70.8 (59-76, n-26) insularis' Santa Cruz Island, Califrnia ( , n-20) ( , n-17) insularis 2 Santa Cruz Island, Califrnia ( , n-22) (99-115, n-27) supercilisa interir Calif, suth central Oregn 93.8 (76-108, n-85) 81.2 (61-98, n-74) nevadae' Great Basin and Arizna 80.3 (69-98, n-56) 73.8 (65-83, n-37) cerulescens Flrida 78.3 (76-80, n-2) 70 (n-l) 'Data frm Pitelka (1951). 2Data frm this study. slight, shrt-term weight lss fllwing the experience f being trapped and handled. Such a physilgical reactin t handling has been described fr a number f migratry passetines {Mueller and Berger, 1966; Leberman and Stern, 1977); the data frm the Santa Gruz Island Scrub Jay suggest that the phenmenn f "handling shck" may als ccur in permanently resident species. In the fllwing analysis f sexual differences in bdy weight and seasnal variatin in bdy weight, nly initial values were utilized in the calculatins fr thse instances in which individual jays were recaptured several times during a tw r three day perid. Mean weight values were used in the analysis f sexual dimrphism in bdy weight when data fr a given individual were available frm several widely separated dates. Pitelka {1951) fund that in all Scrub Jay ppulatins males averaged larger than females in all mrphlgical characters, including bdy weight {Table 1). In the present study, the mean weight f knwn males was grams (n=22}, and the mean weight f knwn females was grams {n=27). The difference between these values is statistically significant at the 95% cnfidence level. Hwever, there is cnsiderable verlap in the weights f males and females {Fig. 1}; this fact, cupled with seasnal bdy weight variatins described belw, makes it difficult t sex with cnfidence mst individuals by weight alne. Pitelka's {1951) mean weights fr insularis were grams {males) and grams {females}; these higher values prbably reflect the fact that Pitelka's sample was c.mpsed mstly f specimens cllected during the fall mnths, when bth sexes shw a tendency t increase slightly in weight. A ttal f 16 individuals (7 knwn males, 5 prbable males, 1 knwn female and 3 unknwn sex) were captured at least nce during each f the fur seasns (spring, March--May 15; summer, May 15--July; fall, August--Nvember; winter, December--February). The mean weight values fr this sample during each f these perids are presented in Table 2. While the differences are nt statistically significant at the 95% cnfidence level due t the small sample sizes and the minr weight variatins invlved (less than 5% f the mean weight f the individual), the mean values d suggest that maximum bdy weights ccur during the fall and minimum bdy weights ccur during the winter. These trends are mre clearly evident frm Figure 2, in which the pattern f weight variatin has been evaluated individually fr each f these 16 repeatedly recaptured jays; 56% f the individuals shwed their maximum weight during the fall mnths and 56% were at their minimum weight during the winter mnths.! suspect that these relatively minr weight variatins, if in fact real and nt merely an artifact prduced by small sample size, mainly reflect the availability f fd during each f these perids. The dates f maximum bdy weights cincide with the presence f an abundant fd supply in the frm f the fall acrn crp; similarly, the minimum bdy weights f the winter mnths wuld appear t fllw the perid f maximum acrn supply and precede the perid f maximum arthrpd abundance in the spring (Atwd, 1978).! have presented elsewhere data indicating the presence f a nn-breeding cmpnent in the Santa Cruz Island Scrub Jay ppulatin (Atwd, 1978). These nn-breeding individuals, which in- Oct.-Dec. '1979 Nrth American Bird Bander Page 149

3 ,I, Knwn (n=27) Knwn c d e (n=22) 1s :2-11 : lo 8 _z 7,, 0c s tu 4 m ß 3 z BODY WEIGHT (grams) Fig. 1. Bdy weights f the Santa Cruz Island Scrub Jay (n--236). Sex indicated where knwn n the basis f breeding characters, vcalizatins, and/r behavir. Fr individuals f knwn sex, sample range (hrizntal bar], mean (vertical bar], and 2 standard errrs f the mean (pen rectangle] are indicated. clude birds ranging frm 1 t at least 3 years f age, frm lse grups r flcks which frage thrughut the year in habitat which appears t be marginal, at least in terms f available territries with suitable nesting sites. Presumably this scial system is assciated with the limited insular envirnment, the lw mrtality rate f fledged jays, and the stability f breeding pairs and territries; sme birds may simply be unable t btain a suitable breeding territry in the packed insular envirnment. Althugh resembling the Flrida Scrub Jay, A. c. cerulescens, in the presence f nn-breeding individuals lder than 1 year f age, the Santa Cruz Island Scrub Jay des nt have the well-develped helper system which characterizes the Flrida subspecies (Wlfenden, 1975; Wlfenden and Fitzpatrick, 1978). In apparent cntrast the prly studied western mainland Scrub Jay ppulatins, in which yearling birds breed at least ccasinally (Ritter, 1972; Verbeek, 1973), I btained n evidence f breeding 1-year-ld Santa Cruz Island Scrub Jays. Althugh data crrelating breeding status with bdy weight in the Santa Cruz Island Scrub Jay are very limited, certain interesting questins are raised by the infrmatin which is available. In cmparing the bdy weights f 9 knwn nnbreeders with thse f knwn breeding individuals n 4 widely separated dates, the weight values f nn-breeders frequently appear t be less than thse f breeders (Fig. 3). Cnclusive analysis f these data is impssible because f the small sample sizes invlved, the weight variatin exhibited by a given sex, and the uncertain sex determinatin f many f the nn-breeding birds included in the sample. Hwever, several bservatins raise Table 2. Annual variatin in bdy weight f Santa Cruz Island Scrub Jays2 Capture Dates Mean Weight (g) 95% Cnfidence Interval March-May May 15-July August-Nvember December-February ' Based n a sample f 16 individuals captured at least nce during each f the fur time perids. Page 150 Nrth American Bird Bander Vl. 4, N. 4

4 ptentially significant questins. Of 3 nn-breeding females lder than I year f age, 2 were exceptinally light weight individuals (96 and 99 grams}; 97% f the ttal sample f 236 bdy weights btained during the study were greater than the weights f these 2 birds. Furthermre, 1 f these small jays is knwn t have been a nnbreeder fr at least 3 cnsecutive breeding seasns, making it the ldest knwn nn-breeder (at least 3 years f age in 1978) I have yet encuntered. Of the 4 nn-breeders f unknwn sex and lder than I year f age, all weighed less than cmparable mean values f knwn breeding males, and 3 f these birds were furthermre at the lw end f the weight range f all knwn males. These facts suggesthat these unknwn sexed birds were either small males r females. Of the five yearling nn-breeders (all f unknwn sex), all weighed less than the cmparable mean values fr knwn breeding males; hwever, this is perhaps less significant than the ther bserved trends, since Pitelka (1951) presented evidence suggesting that yearling Scrub Jays f bth sexes regularly weigh slightly less than lder birds. These data suggestw pssible interpretatins. First, the lack f nn-breeders with heavier weight values culd suggest that mst f the captured nnbreeders were females. The substantiatin f this hypthesis wuld require prf f either a) an inbalance in the sex rati f the ppulatin, r b) a trapping bias resulting in the capture f mre females than males. I feel that bth f these pssibilities are very unlikely (in fact, if any trapping bias was bserved during my study, it was in favr f males being captured mre readily than females). The secnd pssible interpretatin is that nn-breeders d, in fact, average less in bdy weight than established breeders. This might result frm a) small (as well as yung) jays being unable t btain breeding territries r b) nnbreeders being undernurished as a result f being restricted t marginal habitats with less than ptimal fd resurces. The 2 small, knwn female nn-breeders discussed abve were characterized by verall belw-average bdy measurements (bill, tarsus, wing); rather than being "averagesized" birds with belw-average bdy weights, these individuals were small in all bdy characters, including weight. I suspecthat sme nnbreeding Santa Cruz Island Scrub Jays (especially thse lder than I year f age) may be unable, because f their small size, t btain and defend, successfully, suitable nesting territries. The secnd hypthesis, that nn-breeders weigh less as a result f pr fd availability in the marginal habitats where they frage, seems less likely t me. Finally, it shuld be underscred at this pint that relevant data cncerning bdy weights and the individual's breeding status in the ppulatin are s limited that any f the bserved patterns shwn by the presently-available infrmatin shuld be cnsidered as tentative suggestins nly. They d raise sme interesting speculatins as well as indicate the need fr additinal cnclusive evidence. Summary As a result f banding peratins cnducted as part f an nging behaviral study f the Santa loo 8 60 Maximum Weight Sprincj Summer Fall Winter Spring/Fall Summer/Fall løø I Minimum Waight Spring Summer Fall Winter Summer/Fall/Winter Fig. 2. Seasnal variatin in bdy weight f the Santa Cruz Island Scrub Jay. The ccurrence f maximum and minimum bdy weights is shwn fr individuals captured during each f the fur seasns (n=16). Slashed lines (e.g. Spring/Fall) indicate that identical maximum r minimum weight values ccurred during the perids shwn. Oct.-Dec Nrth American Bird Bander Page 151

5 NON-BREEDERS 0 female > 1year ld ß unknwn sex > 1year ld unknwn sex 1year ld ß 5 ß SEP MAR JUL JAN 1977 CAPTURE DATE Fig. 3. Relatinship between bdy weight and breeding status in the Santa Cruz Island Scrub Jay. Range f weight values fr knwn breeders is indicated with vertical bars fr each sex, and hrizntal bars indicate mean values; sample size (n) is prvided underneath vertical bars. Weight values fr knwn nn-breeding individuals are given by indicated symbls. Cruz Island Scrub Jay, large amunts f data were gathered cncerning live bdy weights f this islated subspecies. The mean weight f knwn male Santa Cruz Island Scrub Jays was grams, and that f knwn females grams. Althugh the difference between these values is statistically significant, cnsiderable verlap in the bdy weights f males and females, cupled with minr seasnal variatins in bdy weight, make it impssible t sex many individuals by weight alne. Santa Cruz Island Scrub Jays appear t lse small amunts f weight temprarily as a result f being captured; such a respnse resembles the phenmenn f "handling shck" which has been described in several migratry species. Santa Cruz Island Scrub Jays shw limited seasnal variatin in bdy weight; bth sexes appear t be at their maximum weights during the fall mnths (August--Nvember) and at their minimum weights during the winter mnths (December--February). Althugh far mre study is needed, limited data suggest that nn-breeding Santa Cruz Island Scrub Jays may, n the average, weigh less than cmparably sexed breeding birds. If true, bdy weight (size) may prve t be ne f the factrs invlved in determining the nn-breeding status f these in- dividuals. Acknwledgements I wish t express my gratitude t Drs. Charles T. Cllins, Stuart L. Warter, and Glen E. Wlfenden fr their valuable insights and assistance during this study. Field aspects f this research wuld have been impssible withut the cperatin f Dr. Carey Stantn f the Santa Cruz Island C. and Dr. Lyndal L. Laughrin and Ms. Marla Daily f the University f Califrnia Santa Cruz Island Reserve. Special thanks are due my wife, Judy, fr her patient supprthrughut this study. Financial supprt was partially prvided by the Frank M. Chapman Memrial Fund f the American Museum f Natural Histry, the E1 Drad Audubn Sciety, the Pasadena Audubn Sciety, and Mr. William R. Atwd. Page 152 Nrth American Bird Bander Vl. 4, N. 4

6 Literature cited Atwd, J.L The breeding bilgy f the Santa Cruz Island Scrub Jay, Aphelcma cerulescens insularis. Unpublished M.A. thesis, Califrnia State University, Lng Beach. Barbur, D.B Vcal cmmunicatin in the Flrida Scrub Jay. Unpublished M.A. thesis, Univ. f Suth Flrida, Tampa. Jhnsn, N.K Origin and differentiatin f the avifauna f the Channel Islands, Califrnia. Cndr 74: Leberman, R.C. and M.A. Stern Handlinginduced shck in migrant sngbirds. Nrth Amer. Bird Bander 2: Mueller, H.C. and D.D. Berger Analysis f weight and fat variatins in transient Swainsh's Thrushes. Bird-Banding 37: Pitelka, F.A Pterylgraphy, mlt and age determinatin f American jays f the genus Aphelcma. Cndr 47: Pitelka, F.A Speciatin and eclgic distributin in American jays f the genus Aphelcma. Univ. f Califrnia Publ. Z/. 50: Ritter, L.V The breeding bilgy f Scrub Jays. Unpublished M.A. thesis, Califrnia State University, Chic. Verbeek, N.A.M The explitatin system f the Yellw-billed Magpie. Univ. f Calif. Publ. Z/. 99:1-58. Wenner, A.M. and D.L. Jhnsn. In press. Land vertebrates n the islands: sweepstakes r bridges? In Pwer, D.M. (ed.), The Califrnia Islands: A Multidisciplinary Sympsium. Santa Barbara Natural Histry Museum. Wlfenden, G.E Flrida Scrub Jay helpers at the nest. Auk 92:1-15. Wlfenden, G.E. and J.W. Fitzpatrick The inheritance f territry in grup-breeding birds. BiScience 28: Yeatn, R.I An eclgical analysis f chaparral and pine frest bird cmmunities n Santa Cruz Island and mainland Califrnia. Eclgy 55: Dept. f Bilgy, Calif. State Univ., Lng Beach, CA Present address: Dept. f Bilgy, Univ. f Calif., Ls Angeles, CA Anther rund-trip jurney f a banded bird Ralph W. Dexter Rbert A. Mntgmery reprted (1979) banding a Brwn-headed Cwbird (Mlthrus ater) n 9 June 1971 near Dundee, Illinis, which was retrapped at Hricn, Wiscnsin n 30 August 1971 by Harld Mathiak. Subsequently, it was retrapped again by Mntgmery n 27 June 1972 at the riginal banding site. He als reprted knwing f nly ne ther similar recrd, that published by Amelia R. Laskey n the rund-trip f a Purple Finch (Carpdacus purpureus) (see Mntmgery's nte fr details). Hwever, anther such recrd was verlked. Dexter and Hight (1954) published an accunt f a banded Chimney Swift (Chaetura pelagica L.) which made a rund-trip between Rme, Gergia, and Kent, Ohi (sme 840 km apart). Grdn L. Hight, Jr. banded a swift with # at Rme, Gergia, n 27 September It was retrapped as a freign recvery by me at Kent, Ohi, n 14 May 1954 and retrapped again by Grdn Hight n 19 September 1954 at the riginal banding site in Rme, Gergia. Details f the banding and recveries f this swift and the ther swifts assciated with it will be fund in ur nte published in Bird-Banding. Literature cited Dexter, Ralph W. and Grdn L. Hight, Jr Reciprcal Ohi-Gergia recveries f banded Chimney Swifts. Bird-Banding 25: Mntgmery, Rbert A Rund-trip jurney f a Brwn-headed Cwbird. N. Amer. Bird Bander Department f Bilgical Sciences, Kent State University, Kent, Ohi Oct.-Dec Nrth American Bird Bander Page 153

DORIS J. WATT, C. JOHN RALPH, 2 AND CARTER T. ATKINSON 3

THE ROLE OF PLUMAGE POLYMORPHISM IN DOMINANCE RELATIONSHIPS OF THE WHITE-THROATED SPARROW DORIS J. WATT, C. JOHN RALPH, 2 AND CARTER T. ATKINSON 3 Department f Bilgy, Dickinsn Cllege, Carlisle, Pennsylvania