238 NORTHWESTERN NATURALIST 90(3)

NORTHWESTERN NATURALIST 90:238–243 WINTER 2009

TIMING AND SUCCESS OF BREEDING IN PELAGIC CORMORANTS AT TRIANGLE ISLAND, BRITISH COLUMBIA, 2003–2008

JMARK HIPFNER AND JENNIFER LGREENWOOD

Key words: breeding biology, British Co- There is at present very little information on the lumbia, interannual variability, northeast Pacif- timing and success of Pelagic Cormorant breeding ic, Pelagic Cormorant, Phalocrocorax pelagicus, at colony sites in British Columbia, especially for Triangle Island regions outside of the Strait of Georgia (Drent and others 1964; Harris and others 2005). This Of the 6 cormorant species that inhabit the information is pertinent to understanding causes North Pacific, the Pelagic Cormorant (Phalocro- of regional population change, and given declin- corax pelagicus) is the smallest and most widely ing population trajectories, there is a need for distributed (Hobson 1997). Pelagic Cormorants basic demographic measures. breed from Baja California in the eastern Pacific Triangle Island is situated about 40 km west north to the Bering and Chukchi Seas, and south of Cape Scott off the northwestern tip of across the western Pacific to southern China. Vancouver Island. This site supports one of North America supports an estimated one-third British Columbia’s largest Pelagic Cormorant of the global population of 400,000 birds (Johns- breeding aggregations, comprising over 400 gard 1993), with the bulk breeding in Alaska. breeding pairs in 1989 (Rodway and others Campbell and others (1990) estimated that only 1990). Here we report on a 6-y study (2003– about 4200 pairs bred in British Columbia, 2008) of the timing and success of breeding in mostly at small and widely dispersed sites Pelagic Cormorants at Triangle Island, through centered within the Strait of Georgia. a period of extreme oceanographic variation Information on the population status of along the British Columbia coast (Mackas and Pelagic Cormorants in British Columbia is others 2007). This report constitutes the most limited. Populations appear to have declined comprehensive account of the biology of the over recent decades in the Haida Gwaii archi- species at this comparatively pristine site, and pelago (Fraser and others 1999), although there should provide a baseline against which future is some question about the reliability of the changes can be measured. baseline data (Harfenist and others 2002). More Field crews collected data on Triangle Island conclusive evidence suggests that dramatic (UTM: Zone 09, 0494480E 5634395N, WGS84) declines have occurred in the southern Strait from late March until late August in each year of Georgia (by about 50% since 1987; Chatwin between 2003 and 2007, and from mid-May and others 2002), and along the west coast of until mid-August in 2008. Beginning on arrival Vancouver Island (by about 85% since 1969; in the spring, we logged systematic, detailed Carter and others 2007). The declines have been observations of all cormorant nests situated attributed to disturbance at breeding colonies within the borders of a small cliff-face plot by humans and Bald Eagles (Haliaeetus leucoce- (approximately 25 m2) established in 2002 on phalus), and reductions in prey availability due Puffin Rock, a small islet adjoined to the main to oceanographic change (Chatwin and others island at low tide. Our viewing blind was 2002; Carter and others 2007). Persistent con- situated about 50 m from and 2 m above the tamination and mortality due to oiling and highest nest on the plot, and provided a good fisheries practices might also be contributing view into all nests when adults stood up. factors (Harris and others 2005; Smith and For all active nests, we recorded initial laying Morgan 2005). dates, hatching dates, and dates when a chick

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TABLE 1. Reproductive parameters for Pelagic Cormorants at Triangle Island, British Columbia, 2003–2008. First clutches Replacement clutches Totals No. Chicks Hatch Fledge Successful Hatch Fledge Successful successful fledged, Year n (%) (%) (%) n.(%)1 (%) (%) (%) nests (%) all nests 2003 24 16 (67) 9 (56) 9 (38) 2 (25) 1 (50) 0 (0) 0 (0) 9 (38) 12 2004 20 16 (80) 13 (81) 13 (65) 2 (50) 2 (100) 2 (100) 2 (100) 15 (75) 26 2005 15 2 (13) 0 (0) 0 (0) 3 (23) 0 (0) — 0 (0) 0 (0) 0 2006 13 8 (62) 6 (75) 6 (46) 1 (20) 0 (0) — 0 (0) 6 (46) 9 2007 15 13 (87) 2 (15) 2 (13) 0 (0) — — — 2 (13) 2 2008 0 — — — — — — — 0 0 1 Number and percentage of active nests where the 1st clutch failed to hatch and was subsequently replaced. For example, in 2003, 24 first eggs were laid, of which 16 hatched and 8 did not. Of the 8 eggs that failed, 2 (25%) were replaced.

was no longer present. We used these observa- June in 1989, and in mid-July in 1982, 1984, and tions to determine hatching success (the pro- 1985. Chicks were seen in nests on 19 and 23 July portion of active nests in which at least 1 egg in 1982 (days 200 and 204), with 1 chick described hatched), fledging success (the proportion of as ‘‘40 cm tall, starting to feather’’, suggesting that nests in which at least 1 nestling survived at it was several weeks old. In 1989, Rodway and least 30 d), and breeding success (the propor- others (1990) reported simply that ‘‘most nests tion of nests in which at least 1 nestling held large young’’ in early August. In more recent survived to fledge). To facilitate comparisons years (Triangle Island Research Station, unpubl. of overall production among colonies, however, data), no chicks were seen in 22 nests on 21 June we also report frequency distributions for clutch 1998 (day 172), but 9 of these nests held chicks on size (total eggs), and the number of fledglings 8 July (day 189). Similarly, only 1 of 65 nests held a produced per nest. Because Pelagic Cormorants chick on 26 June in 2001 (day 177), but 5 of these often replace lost clutches, we followed failed nests held chicks on 28 June (day 179). In 2002, the nests and recorded the same set of parameters if 1stchickoftheseasonin32nestshatched a replacement clutch was laid. between 15 and 19 June (days 166 and 170). Based on these observations, it appears that there has Timing of Breeding been little systematic change in the timing of The number of active Pelagic Cormorant nests breeding over recent decades, while timing varied on our monitoring plot varied from 0 (2008) to markedly from year to year (Fig. 1). The same is 24 (2003) across the 6 y, with lower numbers in true at other Pelagic Cormorant breeding sites more recent years (Table 1). The season’s 1st (Boekelheide and others 1990). egg was laid as early as 15 May in 2003 (day The timing of breeding at Triangle Island is 135) and as late as 4 June in 2007 (day 155), similar to that at other sites in British Columbia. while median laying dates varied from 30 May Peak laying occurs between late May and mid- in 2003 (day 150) to 19 June in 2006 (day June at Mandarte Island (Drent and others 170)(Fig. 1). No nests were built and no eggs 1964), and between early June and early July were laid on the breeding plot in 2008. Across in Pacific Rim National Park (Hatler and others all years, individual pairs initiated 1st clutches 1978). Timing at Triangle Island also is similar between mid-May and mid-July. Laying was to that at the Farallon Islands, California, where especially synchronous in 2007 and especially laying peaks in late May (Boekelheide and asynchronous in 2004 and 2005 (Fig. 1). Annu- others 1990), and on Middleton Island, Alaska, ally, replacement clutches were laid at 0 to 25% where laying peaks in late May to mid-June of nests at which the 1st clutch was lost prior to (Hatch and Hatch 1990). hatching (Table 1), and these replacement clutches extended clutch initiation dates to as Clutch size late as 3 August in 2006 (day 215)(Fig. 1). Historical information on timing of breeding at Clutch sizes varied from 1 to 4 eggs in 2003, Triangle Island is sparse. Rodway and others 2004, and 2005, and from 2 to 4 eggs in 2006 and (1990) reported that nests contained eggs in mid- 2007 (Fig. 2). Again, no eggs were laid on the

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FIGURE 1. Timing and success of breeding for Pelagic Cormorants at Triangle Island, British Columbia, in 2003–2007. Laying dates are grouped by 5-d intervals and represent clutch initiation dates. No nests were built and no eggs were laid on the study plot in 2008.

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FIGURE 2. Distributions of clutch size (1–4 eggs, at top) and number of fledglings per nest (0–3, at bottom) of Pelagic Cormorants at Triangle Island, British Columbia in 2003–2007. No pairs bred on the study plot in 2008.

study plot in 2008. There was little seasonal 1990), clutch sizes at Triangle Island were trend in clutch size, although weak seasonal within the normal range for the species; means declines have been reported elsewhere (Boekel- across the northeast Pacific range from 2.5 to 4 heide and others 1990). The modal clutch size eggs, with no geographic cline evident (Hobson was 3 eggs in all 5 y from 2003 to 2007, with 1997; Sydeman and others 2001). means between 2.3 (2005) and 3.2 (2007) eggs. Replacement clutches were somewhat smaller, Breeding success consisting of 2 (in 6 of 8 cases) or occasionally 3 (2 cases) eggs. While Pelagic Cormorants occa- Breeding success at Triangle Island varied sionally lay up to 8 eggs (Campbell and others dramatically over the 5 y of our study: 13 to

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87% of egg-laying pairs hatched 1 or more eggs, Island and other colonies in the Strait of Georgia and 0 to 65% of pairs that hatched at least 1 egg between 1989 and 1994. On the whole, it had 1 or more chick survive to fledge (Table 1). appears that Pelagic Cormorant breeding suc- Overall, at least 1 chick fledged from 0 to 65% of cess at Triangle Island during the 5 y of this 1st clutches, depending on year. Only 2 of 8 study was fairly typical of the species. pairs that re-laid after losing their 1st clutch fledged a chick, both in 2004. Including replace- Acknowledgments.—We thank many field workers ment clutches, 0 to 75% of pairs succeeded for their efforts collecting these data. Funding was annually (Table 1). Of note, no pairs bred provided by the Nestucca Oil Spill Trust Fund, the successfully in 2005, a year of widespread Centre for Wildlife Ecology (Simon Fraser University and the Canadian Wildlife Service), World Wildlife failure for seabird breeding across the Califor- Fund Canada, and the Migratory Birds and Science nia Current system (Sydeman and others 2006). Horizons program of Environment Canada. We In addition, the lack of breeding on the study received invaluable ship and helicopter support from plot in 2008 apparently was due to constant the Canadian Coast Guard. Thanks to M Court, J disturbance from Bald Eagles, possibly associ- Higham, and C Smith for logistical support from ated with inactivity at a Peregrine Falcon (Falco Vancouver. peregrinus) eyrie near the cormorant plot. In other years, the falcon parents kept Bald Eagles LITERATURE CITED out of the area. BOEKELHEIDE RJ, AINLEY DG, HUBER HR, LEWIS TJ. We rarely knew the cause of breeding failure. 1990. Pelagic Cormorant and Double-crested Cor- Most failures occurred after hatching (Table 1), morant. In: Ainley DG, Boekelheide RJ, editors. possibly because chicks simply starved to death Seabirds of the Farallon Islands. Stanford, CA: or were evicted by older and stronger nest- Stanford University Press. p 195–271. mates. Except in 2004, when all 12 clutches laid CAMPBELL RW, DAWE NK, MCTAGGART-COWAN I, on or before the median laying date were COOPER JM, KAISER GW, MCNALL MCE. 1990. The successful compared to only 3 of 8 laid after birds of British Columbia. Vol. I. Vancouver: University of British Columbia Press. 514 p. the median date, there was little systematic CARTER HR, HEBERT PN, CLARKSON PV. 2007. Decline within-season variation in breeding success of Pelagic Cormorants in Barkley Sound, British (Fig. 1). The modal number of fledglings pro- Columbia. Wildlife Afield 4:3–32. duced per nest was 0 in 4 of 5 y; however, in CHATWIN TA, MATHER MH, GIESBRECHT TD. 2002. 2004 the modal number was 2 and 1 nest Changes in Pelagic and Double crested cormorant fledged 3 chicks (Fig. 2). In total, 0 to 26 nesting populations in the Strait of Georgia, British fledgling cormorants were produced annually Columbia. Northwestern Naturalist 83:109–117. from within the borders of our monitoring plot. DRENT RH, VAN TETS GR, TOMPA F, VERMEER K. 1964. Such extreme interannual variation in breed- The breeding birds of Mandarte Island, British ing success appears to be typical of Pelagic Columbia. Canadian Field-Naturalist 78:208–263. FRASER DF, HARPER WL, CANNINGS SG, COOPER JM. Cormorants throughout their northeast Pacific 1999. Rare birds of British Columbia. Victoria: British range. At the Farallon Islands, California, Columbia Ministry of the Environment. 236 p. Pelagic Cormorants produced 0 to 2.4 fledglings HARFENIST A, SLOAN NA, BARTIER PM. 2002. Living per active nest in 11 y (Boekelheide and others marine legacy of Gwaii Haanas. III. Marine bird 1990). More recent analyses suggest little tem- baseline to 2000 and marine bird-related manage- poral change since then (Sydeman and others ment issues throughout the Haida Gwaii region. 2001). Further north, Pelagic Cormorants pro- Halifax: Parks Canada Technical Report in Eco- duced 0.1 to 1.4 fledglings per active nest on the system Science Report No. 036. 164 p. Semidi Islands, Alaska, over 5 y (Hatch and HARRIS ML, WILSON LK, ELLIOTT JE. 2005. An assess- Hatch 1990). Success was more consistent in just ment of PCBs and OC pesticides in eggs of Double- crested (Phalocrocorax auritus)andPelagic(Phalocro- 2 y at Mandarte Island, British Columbia in the corax pelagicus) cormorants from the west coast of late 1950s where 74 and 79% of active nests Canada, 1970–2002. Ecotoxicology 14:607–625. were successful (Drent and others 1964). How- HATCH SA, HATCH MA. 1990. Components of breed- ever, Harris and others (2005) reported consid- ing productivity in a marine bird community: key erably greater variance in reproductive success factors and concordance. Canadian Journal of (0 to 2.0 fledglings per active nest) at Mandarte Zoology 68:1680–1690.

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HATLER DF, CAMPBELL RW, DORST A. 1978. Birds of SYDEMAN WJ, HESTER MM, THAYER JA, GRESS F, Pacific Rim National Park. Victoria: British Co- MARTIN P, BUFFA J. 2001. Climatechange, repro- lumbia Provincial Museum Occasional Paper ductive performance and diet composition of No. 20. 194 p. marine birds in thesouthern California Current HOBSON KA. 1997. Pelagic Cormorant Phalocrocorax system, 1969–1997. Progress in Oceanography 49: pelagicus. Volume 282. In: Poole A, Gill F, editors. 309–329. The Birds of North America. Philadelphia, PA: The SYDEMAN WJ, BRADLEY RW, WARZYBOK P, JAHNCKE V, Birds of North America Inc. 28 p. ABRAHAM CL, KOUSKIE C,HIPFNER JM, OHMAN JOHNSGARD PA. 1993. Cormorants, darters and peli- MD. 2006. Planktivorous auklet Ptychoramphus cans of the world. Washington: Smithsonian aleuticusresponses to ocean climate, 2005: Unusual Institution Press. 445 p. atmospheric blocking? Geophysical Research Let- MACkAS DL, BATTEN S, TRUDEL M. 2007 Effects on ters 33, L22S09. zooplankton of a warmer ocean: recent evidence from the Northeast Pacific. Progress in Oceanog- Centre for Wildlife Ecology, Simon Fraser Univer- raphy 75:223–252 sity and the Canadian Wildlife Service, RR#1 5421 RODWAY MS, LEMON MJF, SUMMERS KR. 1990. British Robertson Road, Delta, British Columbia V4K 3N2; Columbia Seabird Colony Inventory: Scott Islands. [email protected]; Ecosystem Science and Man- Vancouver: Canadian Wildlife Service Technical Report No. 86. 109 p. agement Program, University of Northern British SMITH JL, MORGAN KH. An assessment of seabird Columbia, 3333 University Way, Prince George, bycatch in longline and netfisheries in British British Columbia V2N 4Z9. Submitted 12 Septem- Columbia. Delta: Canadian Wildlife Service Tech- ber 2008, accepted 3 May 2009. Corresponding nical Report Series Number 401. 51 p. Editor: Joan Hagar.

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