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The Breeding Ecology and Social Organization of the Northwestern Crow (Corvus, Caurinus) Was Studied Fron 19 May Ta

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The Breeding Ecology and Social Organization of the Northwestern Crow (Corvus, Caurinus) Was Studied Fron 19 May Ta :. - * - I, 3,~16:i*?p,e labma, @ CA~AD~ANTHESES TH~SESCANADIENNLS rj :'-@,7 , 6 Cartaaa ON MiCROFICHE SUR MICROFICHE - - .. - --. -:as ~re2lingecology and social organization of the Northwestern --- - .. -.. 7 T. TGE CE :A Cr3~(Covus caurinus) on Miflenatch Island, B. C. T , . -- 'ri5 3 ;I&S K)ESEhTED !4aster of Science - _c? CETTi THESE FUT PR~S€NT€E 1 1980 --- ..p. - rt LL T-c~~~E~):ANN/ED'OBTEhiTlCbV DE CE GRADE 5 - ;- $5 -ermy srated to the NATtCYJAL LIWRY OF L'autorisation est, par la prCsente, accordbe B la BIBLIOTH~ 3-.. .-. icr r :rof,lm this thesis and to lerd or 41copies QUE NATIONALE DU CANADA de rnicrofllmer cette prrkse e -<. 'L - de pdtcr ou de vendre des exernplatres du f~h. 1, : + s r r.s otner pub1 icat~onr~ghts, and neitkr the .L'eutew se rCserve les sutres droits de publ~cnr~on111 1 . 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Veuillez prendre connaissance des accompany this thesis. formules d'autorisation qui accompagnent cette thhse. - . 0 m ' THIS DlSSERTATlON 1 LA THESE A ETE H'AS-BEEN MICROFILMED MICROFILMEE TELLE QUE EXACTLY AS RECEIVED NOUS L'AVONS RECUE Otrawa Carada KiA Oh4 OF THE r)N MITCELiFiCP IStA!if), SRITISH COLUMBIA ?ioloqi cal Sciences * I qerebl sP?-- -3 51mnFraser University the right to lend ri * ",is, ~rojcctor ax-endea essay (the title of which is shown below) + -, ; ;the -2 tmcr, =?aser dniversi ty Library, and to make partial or - -2ig c ,; 5; on 1.y +=r s~c*users or , n response to a reabest from the , I;'~T; rLd?y gt%~r,~id9r5itf, or other educational institution, on ,-; ~,.,r ~~t~~lfTC ;SF , ,, zi r "5 users. t further agree thatlpermiss ion -5r mi#ii;leccp/ir,= =f - ,; Lor scholarly purposes may be granted 2, -5 51 tl e Lean s- ;-3$date St~dies. It is.understood that copying , 5- ~c,ti>nsf "15 d2rK 'or financial gain shall not be aiiowed 2 breiding ecology and social organization of the Northwestern Crow (Corvus caurinus) on Xtlenatch Island, B. C. Approval * # yame : Robert i;. Butler -. Degree: ?laster of Science Title of Thesis: The breeding ecology and social organization of the ~. Yorthwestern Crow (Corvus caurinus) on Mitlenatch d Island, B. C. Examining Committee: Cnaindan: Dr. A. i. Turnbull Dr. Y. A. Pl. Verbeek, Senior Supervisor Dr. K. M. Sadlelr m. Kobert C. ErooKe Dr .' d W. Mathewes, Public Examiner . 1.' Date approved 23 &h,\ kq80 iii Abstract The breeding ecology and social organization of the Northwestern Crow (Corvus, caurinus) was studied fron 19 May ta c 30.August 1976, 27 April to 26 .August 1977, and 28 April to 19 a July 1978 on Eitlerlatch Island, British Colunbia. ~i's~la~sofL the Northwestern Crow were similar to those of other species of e crows. Nesting territories averaged 0.50ha. In 1978 nests that were built in continuous woodland were, on average, 21.8m apart. The location of many nests changed little from year to year whi ch suggested strong site tenqci ty. Poundaries extended- about , 2-3m beyond the high tide line in territories that were adjacent ' to the beaches and crows from these territories dominated all other crows on the adjacent stretch of beach, aithough the intertidal was a comunal feeding area. The male crow performed most of the territorial defense which', in beach edge territories, has positively correlated with decreasing-tides during the nesting season. Cnly forced copulations were seen. No courtship behaviour that terminated in copul ation was observed. J Kest building began. in April and most nests .were built in 1 shrubs although ground and tree nest sites were also used. Those nests built in beach-edge territories were si gni ficantly I farther apart than nests built in inland territories. The composition and construction of 32 nests is described. The eggs were laid beginning in late April after a mean . of 8.6 days following the completion of the nest. Crows that estatl ished new territories waited significantly longer to lay - -. i their eggs than crows that used the same territory f+rsm the .. ~reviousyehr. Clutches were initiated over 37 and 32 days in 7- - 1977 and 1978, respectively. The mean clutch size was 3.7 and -" 1. 3.8 egq5 in 1977 and 1978, respectively. Clutches were - ;-..: ', siqni ficantly larger in beach-edcje territories than inland . tecri tories. The eggs cdurinus were incibated only the female and lost ah average of 0.18 q per day (19.3% bf original weight during incubation). The female-crow was highly attentive to her eaqs and only left them to be fed by the male and for short maintenance activities. Incubation lasted f6r 18 days. In 1977, 39% aild in 1978, 52% of laid eggs hatched, which is' much lower than for the Common Crow (C.- brachyrhynchos) + .-.. in California. /' The female attentively brooded the nestlinqs until they ,,/ ,' were about 10 days old. The tlorthwestern Crow nestlings qrew faster, on average, than Common Crow nestlinqs. The male per- formed about 66%'of the feedinas until the nestlings reached 7 days of aqe and afterward the female fed th'e nestlings' about 66% of the feedings until fledging age. Most nestlinqs were lost in the first week of life, probably to other crows. About 52% of the hatched e-qgs fledged young in 1976-78, much hioher than California Common Crows (13%). Fledging occurred in June f-- and early ~ulywhen the nestlings were 26:days old, on average, and weiqhed 318.1' 9. Fledging success (no. of eggs laid that 1 fledqed young) was 27.1%("Pn 1977 and 16.8% in 1978. Beach-edge ' territories lbst sjsnificantly few,er nestlinqs and fledged significantly more young than inland territories. Juvenite crows 14ft the territory about 2 weeks after ' %-fledqinq ind still beqGd fiod from their parents in late AuQust when my observation; ended. The ,roosts cornorised of the male roost, pair roost, yearling roost, and a famil* roost, on the territory ind a . O communal roost off\ t -&erri tory. '- :The food of the tiorthwestern Crow came from' the beach, the' 2, - - .4 2 meadow, and &be qull coTony? . The crows shkred a significant >. ; preference for .,the b'each as a food source over the meadow and gu1 t &tony, +?- I * I .r, Sorw yearlinq crows helped their parents raise the . I nestl'ings.' However, most a,wf pairs did not have yearling F \ helpers. Yearlings assisted in territorial defense a occasion 'fed t'h e- nestlings-. In return they were fed , -P adults. Those adults wj th. helpers had larger clutches, more d nest1 i rigs, and more. i .. fled@ i ngs than adults without helpers. ; he pre;ence of the Northwestern Crow nestlings coincided . b. with the, period of 'food abundance 06 the beach, in thk meadow, / , ' . and in the gulf~colony. '. A,lthough Horthwestern Crow nests are clumped I suggest that. ,. the dispersion of nests sn the is1-and has arisen in response to the availability of nest sites and not a strategy to exploit the d food supply. w -.- I suggest that nesting asynchrony is a response to the abi 1i ty of oai rs to establish nesting terri toiles in spring. Thqse crows that nested in new territories.were less synchronous ' in laying t Celr eggs than pairs reusing the previpus years' , territory. -. ='\ The N 4rthwestern Crow appears to be a solitary nester that ' 19t ' has incorporated some non-breedinq year1 ing crows into. the 3 breeding' effort. I suyest that its social orqanization js a resoonse to the nature of the availability of the food. resource. In a time when tides were absent from the earth, the ~a'ven, Klook-shood, stole the daughter of Tu-ch~e,the East Wind, for his wi Fpr AS a marriage pre,sent ,*Tu-'chee promised * to bare the mud-flats fo'r twenty days so that Raven, beinqI' a I shjftless fellow, could find easy 'prey. "Good", saM the lazy Raven., "but you must bare the land to the cape"; to which the East di.nd replied, "Ho, I will make' I it dry for only a Cew feet." The hagglinq weny on and on until Kaven finally threatened to return the.daughter.
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