REPRODUCTIVE PERFORMANCE OF : THE IMPORTANCE OF POPULATION AND COLONY SIZE

GEORGEL. HUNT, JR., ZOE A. EPPLEY,AND DAVID C. SCHNEIDER• Departmentof Ecologyand Evolutionary Biology, University of , Irvine,California 92717 USA

ABSTRACT.--Wecompared reproductive performance of five speciesof seabirdsat two colonies,St. George Island (2.5 million ) and St. Paul Island (250,000birds), in the southeasternBering Sea.All specieshad lower chick growth ratesat the larger colony,and the differenceswere statisticallysignificant in four species.Fledge weights of Common Murres ( aalge)on St. GeorgeIsland were 84-88% of thoseon St. Paul. Averagefledge weights of Thick-billed Murres (Uria lomvia)on St. Georgewere only 74%of thosefor chicks from St. Paul. We found no significantdifferences in clutchsize or breedingsuccess between populationsbreeding at the two colonies.For three species,Black-legged Kittiwakes (Rissa tridactyla),Common Murres, and Thick-billed Murres, we extendedour analysisto include publisheddata from other colonies.We examinedbreeding performanceas a function of colony size, populationsize (suggestiveof intraspecificcompetition), and "effectivecolony size," the sum of the populationsof specieswith considerabledietary overlap (suggestive of interspecificcompetition for food). We found consistentlynegative relationships between population size and several measuresof breeding performance(clutch size, growth rate, fledgeweight, and breedingsuccess). In addition to the lower breeding successat colonies that supportlarge populations,chicks from thesecolonies may be subjectto higher postfledg- ing mortalitybecause of fledgingat lower weights.Received 7 January 1985, accepted 18 October 1985.

THEREis now mounting evidence that repro- species in and found a ductive performance in colonies may negative relationshipbetween the size of the vary with population or colony size. Coulson population at a colony and the size of popula- et al. (1982) documentedchanges in reproduc- tions of the same species at nearby colonies. tive performancethat could be related to intra- They hypothesized that this relationship was specificcompetition for food. They found ear- due to density-dependent depletion of prey lier breeding and increased size in a near colonies. In a review of recent work, Birk- Herring (Larusargentatus) colony after it head and Furness (1985) concluded that nega- had been culled to one-quarter of its former tive relationshipsbetween population size and size. Hunt et al. (1981, 1982)suggested that col- several aspects of reproductive performance ony size may affect reproductiveperformance support the hypothesisthat intraspecificcom- in relatively stablecolonies such as thoseof the petition for food near coloniesmay regulate Pribilof Islands.More recently,Gaston (in press) seabird populations. found a negativerelationship between fledge Seabirdscommonly breed in large, multispe- weight and population size for Thick-billed cies colonies and may have considerable di- Murres (Uria lornvia)and for Atlantic Puffins etary overlap with other speciesat the colony (Fraterculaarctica) in data from seven colonies. (Belopol'skii 1957, Pearson 1968, Croxall and Gastonet al. (1983) measuredfledge weights of Prince 1980, Hunt et al. 1982). Hence, both in- murre chicks at three colonies within the same tra- and interspecific competition are possible. year and found a negative relationship be- Belopol'skii (1957) attributed reduced breeding tween population size and fledge weight. Fur- successand dietary changesin Black-legged ness and Birkhead (1984) examined four sea- Kittiwakes (Rissatridactyla) to competition with Thick-billed Murres for food in years of low fish availability. Ashmole (1963) first suggested • present address: Newfoundland Institute of Cold that competition for food around breeding col- Ocean Science,Memorial University of Newfound- onies may regulate seabirdpopulations. land, St. Johns,Newfoundland A1B 3X7, . If there are negative relationshipsbetween

306 The 103: 306-317. April 1986 April1986] ReproductivePerformance ofSeabirds 307 population or colony size and reproductive T^BLE1. Population sizes of seabirdsbreeding on performance, then the greatest effects should the Pribilof Islands (from Hickey and Craighead 1977). be seen in the largest populationsor colonies. St. George Island supportsa seabird colony of St. George St. Paul 2.5 million birds, of which 1.5 million are Thick- Island Island billed Murres (Hickey and Craighead 1977). Northern Fulmar (Fulmarus This colony is one of the largest in the North- glacialis) 70,000 700 ern Hemisphere and is the largest for which Red-faced Cormorant (Phala- reproductiveinformation for severalspecies is crocoraxurile) 5,000 2,500 available. For 3 yr we comparedseabird repro- Black-leggedKittiwake (Rissa tridactyla) 72,000 31,000 duction at St. George Island and at a similar Red-legged Kittiwake (R. bre- but smaller colony on St. Paul Island. The latter virostris) 220,000 2,200 colony, consistingof 253,800 birds, is 63 km Common Murre (Uria aalge) 190,000 39,000 distant and supportsthe samesuite of species Thick-billed Murre (U. lorn- via) 1,500,000 110,000 as found on St. George Island. Although the ParakeetAuklet (Cyclorrhyn- proportions of species change between the chuspsittacula) 150,000 34,000 colonies(Schneider and Hunt 1984),all species LeastAuklet (Aethiapusilla) 250,000 23,000 are more abundant on St. GeorgeIsland (Table Crested Auklet (A. cristatella) 28,000 6,000 1). We comparedreproductive performanceof Horned Puffin (Fraterculacor- niculata) 28,000 4,400 five speciesof seabirdsto look for evidenceof Tufted Puffin (F. cirrhata) 6,000 1,000 density-relateddepression of reproduction. Total 2,519,000 253,800 In addition, we examined reports of kitti- wake and murre reproductiveperformance in other colonies to determine whether a den- sity-dependent relation exists generally. To fore egg-layinguntil chickdeparture or failure. Sam- pie sizesare given in Table 2. Breeding successwas partition the possibleeffects of intra- and in- computedfor eachstudy area, using the ratio of chicks terspecificcompetition, we also examined re- fledged to the number of breeding attempts(defined productive performancefor negative relation- as a defended territory or breeding site/ con- ships with population size (indicating struction).For comparisonwith publishedwork on intraspecificcompetition) and "effective col- kittiwakes,we usedchicks fledged per completednest ony size," the sum of specieswith considerable (= pair) as a measureof breeding success.Breeding dietary overlap (indicating interspecificcom- success in murres was estimated as the number of petition for food). The resultsof thesecompar- chicksthat departedsuccessfully, divided by the av- isons suggestwhether reproduction in North- eragenumber of adultsat eachsite during incubation and brooding. We assumedmissing murre chicks to ern Hemisphere seabirds generally shows have departedsuccessfully if their age or density-dependenceand the relative impor- on the previousvisit indicatedthat they were at least tance of intra-and interspecificcompetition. 3 weeks old. We computedthe number of murre chicks"fledged" per pair that laid egg(s) for com- METHODS parisonwith other studies.Red-faced Cormorants and Black-leggedKittiwakes laid multiple-eggclutches at Breeding seabirdswere studied at St. Paul and St. the Pribilof Islands.Clutch size was calculatedusing Georgeislands, Pribilof Islands,southeastern Bering only nestscontaining . Sea,during the summersof 1976, 1977,and 1978 (see Growth ratesand fledge weights were obtained at Hunt et al. 1982 for a detailed account). We measured two sitesaccessible by ladder on St. George and at clutchsize, growth rate, fledge weight, and breeding three sites on St. Paul. Study sites were visited at 3- successin Red-facedCormorants (Phalacrocorax urile), 4-day intervals, except when weather prevented. Black-leggedKittiwakes, Red-legged Kittiwakes (Ris- Growth rates were calculated as the difference be- sabrevirostris), Common Murres (Uria aalge), and Thick- tween the initial weighing and the peakweight mea- billed Murresat both colonies.Throughout the study, sured,divided by the number of dayselapsed. Fledge methodsand frequencyof site visits by study teams weights were the last weights of chicksobtained be- on the two islandswere as similaras possible. fore fledging,or departurein the caseof murrechicks. Clutch size and breeding successwere estimated We useda one-way ANOVA (Sokaland Rohlf 1969) at three sites on St. George Island and at four sites to determinewhether sitesand yearscould be pooled on St. Paul Island. We visited each site at 3-4-day to compareislands. Years could not be pooled so we intervalsto follow the progressof breedingfrom be- used t-teststo comparecolonies within each year. If 308 HUNT, EPPLEY,AND SCHNEIDER [Auk, Vol. 103

TABLE2. Sample sizes used in comparisonof reproductiveperformance of seabirdsat St. Paul (STP) and St. George (STG) islands.a

Red-faced Black-legged Red-legged Thick-billed Cormorant Kittiwake Kittiwake Common Murre Murre

STP STG STP STG STP STG STP STG STP STG

Clutch size nv nv nv nv nv nv 1976 13 10 70 19 1977 49 17 102 70 1978 84 37 110 39

Growth rate 1976 17 11 33 24 4 12 5 4 16 23 1977 4 14 22 20 3 42 9 3 17 34 1978 8 16 16 16 nd 13 nd 12 16 25 Fledge weight 1976 nd nd 14 8 4 28 5 4 16 23 1977 nd nd 21 20 3 29 11 3 17 34 1978 nd nd 15 16 nd 11 nd 12 16 25 Breeding success 1976 93 7 127 34 76 88 70 11 96 40 1977 57 32 157 99 78 164 30 15 155 92 1978 87 66 208 136 112 187 76 38 177 131

and = no data, nv = no variation.

the difference between the two colony means re- t-tests,and probabilitieswere calculatedfor one-tailed versed direction among years (e.g. greater at St. Pau! tests. one year and greateron St. Georgeanother year), we Effectivecolony size was calculatedfor a colonyby acceptedthe null hypothesisof no consistentdiffer- summingthe populationsof specieswhose diets were ence between colonies. If the difference between col- likely to overlap those of kittiwakes and tourres. ony means was consistent among years, we com- Speciesincluded in the calculation of effective col- bined test resultsfrom all years using Fisher's(1954) ony size are listed in the Appendix. We usedoverlap method. in a very broad senseand excludedonly speciesthat To test whether reproductive achievement showed fed very far offshore(Manx Shearwater,Puffinus puf- density-dependenceat other locations (see Appen- finus),on different-sizeprey (cormorants),or on dif- dix), we assembledpublished data on Black-legged ferent prey (planktivores). Kittiwakes (BLK), Common Murres (CM), and Thick- billed Murres (TBM). When studiespresented several RESULTS years of data, we used only the maximumvalue, as this providesa measureof how well pairsin a colony Comparisonof reproductiveperformance at the of a particular size can do. Additionally, multiple- year studieswere more likely to report a year of re- PribilofIslands.--We found no significant dif- productive failure than single-year studies; these ferences in clutch size or breeding successof failures often were due to stochastic factors (e.g. seabird populationsat St. Paul and St. George weather). The use of maximum values reduced the (Table 3). There were significantdifferences in bias different lengths of study (years) introduced to chick growth rates and fledge weights that, al- estimatesof average breeding success.We examined though not affecting reproductive successdi- clutch size (BLK), growth rates (BLK, CM, TBM), rectly, may affectlater survivorshipof chicks. fledge weights (CM, TBM), and breeding success All five specieshad lower chick growth rates (BLK, CM, TBM). For each species we calculated at the larger colony (Fig. 1, Table 3), although Pearsonpartial correlation coefficientsfor each re- the difference was not statistically significant productive measureagainst colony size, population size, and effective colony size. The partial correla- for Red-legged Kittiwakes. The largest differ- tions representthe unique effectsof colonysize, pop- encein growth rate was in Thick-billedMurres, ulation size, and effectivecolony size; the intercor- with growth ratesat the larger colonyonly 59% relation between these variables has been removed. of those at the smaller colony. Murre chicks The partial correlationcoefficients were testedusing leave the colony when they are three weeks April1986] ReproductivePerformance ofSeabirds 309

TABLE3. Differencesin reproductive parametersof seabirdsbreeding on St. Pau! (P) and St. George (G) islands.a Probability levels basedon Fisher's(1954) method to combine tests (years). RFC = Red-faced Cormorant,BLK = Black-leggedKittiwake, RLK = Red-leggedKittiwake, CM = CommonMurre, TBM = Thick-billed Murre.

RFC BLK RLK CM TBM

Clutch size P < G •s P > G •s nv nv nv Growth rate P > G** P > G* P > G ns P > G* P > G** Fledgeweight nd flips flips P > G* P > G*** Breedingsuccess flips flips flips flips flips and = no data,nv = no variationin clutchsize, flips = directionnot consistentfrom year to year; ns = not significantat P = 0.05, * = P < 0.05, ** = P < 0.005, *** = P < 0.001. old and about20% of adult weight. Murre chicks be the result of subspeciesdifferences in adult of both speciesdeparted St. George Island at size. We had sufficientdata to examine growth substantiallylower weights than chicks from rates for two subspeciesof Thick-billed Murre the smaller colony; mean fledge weight of (U. I. lomviaand U. I. arra; Fig. 3) and found Thick-billed Murre chicksfrom St. Georgewas negative correlationswith population size in only 74% of that of chicksfrom St. Paul. Lower both cases.It seemsunlikely that the negative growth rates in the two kittiwake speciesand correlations found in the combined analyses Red-facedCormorants at St. George did not re- (Fig. 2) are the result of our inclusion of data suit in lower fledge weights. These chicksre- from more than one . main in the nest until nearly adult size, and birds on St. George Island completedgrowth DISCUSSION before fledging. Density-dependenceof kittiwake and murrere- Our study provides strong inferential evi- production.--Whenwe examined the effect on dence for density-relateddepression of repro- reproductiveperformance of population size, ductive achievement in seabirds. At the Pribi- colony size, and effective colony size, repro- lof Islands,we found significantlylower growth ductivemeasures showed the mostconsistently rates in four species, and, for murres, lower negativerelationships with populationsize (Fig. fledgeweights at the larger colony.Using pub- 2). Partial correlationsfor population size were lished data for other colonies,we found nega- negative in 9 of 9 cases(4 significant, P < 0.05). tive relationshipsbetween population size and We combinedprobabilities (Fisher 1954) for the clutch size, growth rates,and breeding success partial correlationsfor measureswe thought in Black-leggedKittiwakes, and growth rates, were independent (BLK growth rate, breeding breeding success,and fledge weight in Com- success;CM breeding success,fledge weight; mon and Thick-billed murres.We used partial TBM breeding success,fledge weight) and ob- correlationanalysis to determinethat popula- tained a significant negative relationship be- tion size, rather than colony size or the size of tween population size and reproductive per- potential competitor populations, is the most formance (P = 0.0076, X 2 = 27.0501, 12 df). important factor. We have not eliminated the Partial correlationsbetween colony size and re- possibility that population size covarieswith productiveperformance were negative in 1 of some undetermined causal factor, nor have we 9 cases(none statisticallysignificant), and those determinedthe mechanismby which popula- for effectivecolony size were negative in 4 of tion size effectsreproductive performance,al- 9 cases(again, none statistically significant). The though we have suggestiveevidence. generally positivepartial correlationsfor col- Competition for nest sitesis important at sea- ony size (8 of 9 cases)were suggestiveof a pos- bird colonies(Squibb and Hunt 1983)and may itive relationship,but a two-tailed t-testshowed affect the species composition of colonies no statisticallysignificant relationship between (Whittam and Siegel-Causey1981). Nest-site colony size and reproductiveperformance. defensein the faceof strongcompetitive pres- We consideredthe possibilitythat the neg- sure could increasethe energy expenditureof ative correlation between population size and pairs and might potentially influence the en- growth ratesor fledge weights of murres might ergy allocatedto eggs.However, site competi- 310 HUNT, EPPLEY,AND SCHNEIDER [Auk, Vol. 103

FACED CORMORANTRED-

BLACK- i • LEGGEDKITTIWAKE

• RED- •1.0 LEGGED • 0.5 KITTIWAKE hi g • 0.5i.o MURRECOMMON

THICK- BILLED r MURRE 76 77 78 76 77 78 76 77 78 YEAR Fig.1. Comparisonof reproductiveperformance of seabirdpopulations on St.Paul (hatched bars) and St. George(solid bars) islands for five speciesof cliff-nestingseabirds, 1976-1978. Figures show mean + 1 SD. tion is most intense early in the breeding sea- on reproductive performance. In contrast, in- son when sites are being established and terference during foraging should affect only declines thereafter. It is difficult to envision thosespecies that feed togetherand should be how nest-sitecompetition directly could cause greatestwithin a speciesor a foraging type. the differencesin chick growth ratesand fledge Kittiwakes feeding on ephemeral prey that weights that we found correlatedwith popu- schoolat the surfacemay easilyinterfere with lation size. each other or may cause the prey to disperse. Competitionfor foodmay affect directly chick Likewise, interference among murres during growth ratesby reducingfood delivery rates, feeding seemslikely where they feed in dense if not the total amount delivered to chicks. aggregations(e.g. >1,000 birds/km2), as has Competitionmay depressthe resourcebase, or been found at St. George Island (Ford et al. birds competingfor prey may interfere with 1982, Schneider and Hunt 1984). The negative othersduring prey capture.Large numbers of correlationsbetween population size and re- birds feeding in an area might reduce the re- productiveperformance are consistentwith an sourcebase, thereby decreasing prey availabil- interference mechanism. ity. Seabirdsbreeding at moderate-sizecolo- Arctic colonies tend to be large, supporting niesmay reduce fish standing stocks in the area largepopulations. If reproductionin arcticcol- (Furness1978, Furness and Cooper 1982).There onies tends to be less successfulthan repro- has been no direct demonstration, however, of duction in subarcticor temperatecolonies due resourcedepletion around seabird colonies. If to a latitudinal effect,then our correlationsmay resourcedepletion occurs, it shouldaffect all be misleading.Most of the colonieswe usedin speciesusing the depletedprey. However,our this analysisare subarctic,as they occurin the analysisshows no effectof effectivecolony size area between the 5øCand 15øCAugust sea sur- April 1986] ReproductivePerformance of Seabirds 311

p=0097 ß M p=0041 20 ßK 20©I eM•sßL ]8 o• 18t6 'Q ßNR•AiOß BLACK-LEGGEDKITTIWAKE 22i4I ew , ','T'L•, r:051152ßv ]41e] r,078761 14 D, oo46 ]02 ]0$ lO4 105 .v:x .... 240 COMMON • o.7 200 •o • 220180 ßc IMURRE

24o ß ßH TRIOK-BILLED ,,-;J Z •FEE,. B MURRE

POPULATION SIZE

Fig. 2. Relationshipbetween reproductive performance and populationsize for Black-leggedKittiwakes, CommonMurres, and Thick-billed Murres. Lettersdesignate colonies listed in the Appendix. Partial corre- lations and probabilitiesare given. face isotherms (Tuck 1961). Four colonies (Ak- tive success(a bird's lifetime achievement)may patok Island; Cape Hay, Bylot Island; Prince be even more profound than our results sug- Leopold Island; Coburg Island) are arctic colo- gest, through the production of underweight nies and have large Thick-billed Murre popu- young. Low fledge weight has been associated lations. No substantial differences were evi- with decreasedpostfledging survival rates in dent, however,in the reproductiveperformance seabirds (Perrins et al. 1973, Jarvis 1974), al- of subarctic and arctic colonies of similar size though studiesof Atlantic Puffins (Harris 1982), (Fig. 2). Independently, Gaston et al. (1983) (Alca torda;Lloyd 1979),and Com- found a negativerelationship between fledge mon Murres (Hedgren 1981) failed to show an weight of Thick-billed Murres and population effect of fledge weight on survivorship. These size in these four colonies. Thus, differ- three studies were done on colonies with in- encesthat potentially covary with population creasing populations (D. N. Nettleship pets. size are not a factor. comm.). In Razorbills and Common Murres, Mahoneyand Threlfall (1981)suggested that parental feeding of young at seamay compen- slowerchick growth rates at arcticcolonies may satefor low fledgeweight. However, body size be due simply to lower ambient temperatures, profoundly affects thermoregulatorycosts of requiring chicks to allocate more energy to precocialchicks, and large body size is critical thermoregulationand less to growth (but see for chicks'thermal defensein water (Eppley Birkheadand Nettleship 1984for a critique of 1984). Large chick size and relatively mild sea their results).Ordinarily, broodingwould pro- temperaturesmay be the reasonHedgren (1981) tect chicksfrom the high costsof thermoreg- found no effect of fledge weight on survivor- ulation. At arctic colonieswith large popula- ship in Common Murres. The smallestsize class tions, however, parents may spend more time of chicksused in Hedgren's analysiswas 28% foragingand leave chicksexposed longer or at an earlier age, exacerbatingtemperature ef- fects.In our analysis,the majority of colonies •16 (e) arra r:-0.230 with small populationsof kittiwakes or tourres ß (0) lornviar=-0.679 are in warmer ocean areas or at lower latitudes o o than the largest colonies. Nevertheless, low 10 o ß temperature alone cannot account for Gaston 8 ß o o et al.'s (1983) observationof a negative rela- o tionship between feeding ratesfor chicksand I i population size at nearby arctic colonies,nor 4104 105 106 107 doesit explain negative correlationsfor clutch POPULATION SIZE size or breeding successin our results. Fig. 3. Growth rates for subspeciesof Thick-billed Density-dependentdepression of reproduc- Murres as a function of population size. 312 HUNTßEPPLEY, AND SCHNEIDER [Auk,Vol. 103 heavier than the average fledge weight of the BAIRD,P. A., & M. A. HATCH. 1979. Breeding biol- samespecies on St. George Island. ogy and feeding habits of seabirdsof Sitkalidak Previous attempts to determine limits to sea- Strait, 1977-1978. Environmental assessment of bird reproductiveperformance have tested the the Alaskan Continental Shelf. Annual reports of principal investigators. Boulder, Colorado, abilities of pairs to raise artificially increased Natl. OceanicAtmospheric Admin. Environ. Res. broods.However, the ability to raiseadditional Lab. 2: 107-186. young also appearsto be negatively related to BARRETT,R. T., & O. J. . 1980. Growth and population size. Among Atlantic Puffins, pairs survival of nestling Kittiwakes Rissatridactyla in at (16,000 puffins) raised extra young . Ornis Scandinavica 11: 228-235. (Corkhill 1973a),while pairs from Great Island BELOPOL'SKII,L.O. 1957. Ecologyof sea bird colo- (480,840 puffins) failed to raise extra young nies of the . Jerusalem, Israel Pro- (Nettleship 1972). gram for Sci. Transl. We suggestthat many facets of seabird re- BIRKHEAD,T. R. 1977. Adaptive significanceof the nestling period of (Uria aalge).Ibis productive performanceare negatively related 199: 544-549. to population size, and that these in turn may --, & R. W. FURNESS.1985. Regulation of sea- influence postfledging survivorship. We need bird populations. Pp. 145-167 in Behavioural to use caution in modeling population dynam- :ecological consequences of adaptive be- ics of large seabird populationsbased on pa- haviour (R. M. Sibley and R. H. Smith, Eds.). The rametersobtained in smallpopulations. If man- 25th Symp.of the BritishEcol. Soc., Reading 1984. agement models for large seabird populations London, Blackwell. use survivorship values obtained from small --, & P. J. HUDSON. 1977. Population parame- populations,and ignore density-dependentin- ters for the Common Uria aalge.Ornis fluences,then predictions concerning popula- Scandinavica 8: 145-154. tion recoveryrates are likely to be misleading. --, & D. N. NETTLESHIP.1981. Reproductive bi- ology of Thick-billed Murres (Uria lomvia): an inter-colony comparison.Auk 98: 258-269. ACKNOWLEDGMENTS --, & . 1984. Foodintake and weight in- crements of Common Guillemot chicks: a com- We thank the Aleut communities of St. Paul and ment. Ibis 126: 421-422. St. George for permissionto work on their lands and BROWN, R. G. B., D. N. NETTLESHIP, P. GERMAIN, C. E. the Pribilof Island Program of the National Marine TULL, & T. DAVIS. 1975. Atlas of eastern Cana- Fisheries Service (in particular, J. Adams, K. Dzim- dian seabirds. Ottawa, Ontario, Canadian Wildl. bel, A. Groves,R. Hajny, J. R. Merculief, J. Scordino, Serv. and H. Thayer). The following people helped with BRUN,E. 1979. Present statusand trends in popu- fieldwork: B. Braunß D. Forsell, J. FrancisßJ. Johnsonß lations of seabirds of Norway. Pp. 289-302 in J. Koelling, B. MayerßD. Merculief, G. McGlashon,P. Conservation of marine birds of northern North Merculief, M. Naughton, L. Philemonoff, M. Pitts, A. America (J. C. Bartonekand D. N. Nettleship, Prokopiof,W. Rodstrom,M. Roelke,D. Schwartz,S. Eds.).Wildl. Res.Rept. 11. ,D.C., U.S. Sharr, D. Siegel-Causey,R. Squibb,and M. Warner. Fish Wildl. Serv. Data managementwas aided by G. Bush, M. Craneß CORKHILL,P. 1973a. Food and feeding ecology of J. Kaiwi, J. Mershman, and H. Petersen. D. Heine- puffins. Bird Study 20: 207-220. mann, A. J. Gaston,and D. N. Nettleship provided useful comments on an earlier draft of the manu- 1973b. Manx Shearwaterson Skomer:pop- ulation and mortality due to gull predation.Brit- script. This work was supported in part by the Na- ish Birds 66: 136-143. tional Oceanic and Atmospheric Administration COULSON,J. C. 1963. The status of the Kittiwake in (through interagencyagreement with the Bureau of the British Isles. Bird Study 10: 147-179. Land Management, under which a multiyear pro- ß N. DUNCANß& C. THOMAS.1982. Changes gram responding to the needs of petroleum devel- in the breeding biology of the Herring Gull (La- opment of the Alaskan continental shelf is managed rus argentatus)induced by reduction in the size by the Outer Continental Shelf Environmental As- and density of the colony. J. Anita. Ecol. 51: 739- sessmentProgram) and by NSF grants DPP 79-10386 756. and DPP 82-06036 to G. L. Huntß Jr. --, & C. S. THOMAS. 1985. Changesin the bi- ology of the kittiwake Rissatridactyla: a 31-year LITERATURE CITED study of a breeding colony. J. Anita. Ecol. 54: 9- 26. ASHMOLE,N.P. 1963. The regulation of numbersof ß & E. WHITE. 1958. Observations on the tropical oceanicbirds. Ibis 103b:458-473. breeding of the Kittiwake. Bird Study 5: 74-83. April ! 986] ReproductivePerformance ofSeabirds 313

ß& . 1961. An analysisof factorsinflu- weight of the puffin Fraterculaarctica. Ibis 124: encing the clutch size of the Kittiwake. Proc. 100-!03. Zool. Soc. London !36: 207-2!7. HATCHß $. A., T. W. PEARSON,& P. J. GOULD. 1979. CRAMPß$., W. R. I•. BOURNEß& I•. SAUNDERS. 1974. Reproductiveecology of seabirdsat Middleton The seabirds of Britain and . Londonß Island, . Environmental assessment of the Collins. Alaskan Continental Shelf. Annual reports of CROXALL,J. I•., & I•. A. PRINCE.1980. Foodßfeeding principal investigators.Boulderß Colorado, Natl. ecologyand ecologicalsegregation of seabirdsat OceanicAtmospheric Admin. Environ. Res.Lab. South Georgia.Biol. J. Linnean Soc. !4: !03-13!. 2: 233-308. CULLEtq,E. 1957. Adaptations in the Kittiwake to HEDGREN,$. 1980. Reproductivesuccess of Guille- cliff-nesting.Ibis 99: 275-302. mots Uria aalge on the island of Stora Karlso. DRURY,W. H., C. RAMSDELLß& J. B. FRENCHßJR. 1981. Ornis Fennica 57: 49-57. Ecologicalstudies in the BeringStrait region. En- !981. Effectsof fledging weight and timing vironmental assessment of the Alaskan Conti- of fledging on the survival of Guillemot (Uria nental Shelf. Final reportsof principal investi- aalge)chicks. Ornis Scandinavica12: 5!-54. gators. Boulderß Coloradoß Natl. Oceanic ß & A. LINNMAN. 1979. Growth of Guillemot AtmosphericAdmin. Environ. Res. Lab. 11 Biol. Uria aalgechicks in relation to time of hatching. Studies: 175-488. Ornis Scandinavica 10: 29-36. EV?LE¾,Z.A. !984. Developmentof thermoregula- H•CKE¾,J. J., & F. L. CRAIG•EAD. 1977. A census of tory abilities in Xantus' Murrelet chicksSynthli- seabirds on the Pribilof Islands. Environmental boramphushypoleucus. Physiol. Zool. 57: 307-3!7. assessment of the Alaskan Continental Shelf. FIRSOVAßL. V. 1978. [Breeding biology of the Red- Annual reports of principal investigators.Boul- legged Kittiwake, Rissabrevirostris (Bruch), and derß ColoradoßNatl. Oceanic Atmospheric Ad- the Common Kittiwake, Rissatridactyla (Lin- min. Environ. Res. Lab. 2: 96-!95. naeus)ßon the .] In System- HUNTß G. L., JR., Z. EPPLEY,B. BURGESON,& R. SQUIBB. aticsand biology of rare and little-studied birds. 1982. Reproductiveecologyß foods and foraging LeningradßUSSR, Zool. Inst. Acad. Sci. areasof seabirdsnesting on the Pribilof Islandsß FISHERßR.A. !954. Statistical methods for research !975-!979. Environmental assessment of the workersß!2th ed. EdinburghßOliver and Boyd. AlaskanContinental Shelf. Final reportsof prin- FORD,R. G., J. A. WIENS,D. HEINEMANN,& G. L. HUNT. cipal investigators. Boulderß Coloradoß Natl. !982. Modelling the sensitivity of colonially OceanicAtmospheric Admin. Environ. Res. Lab. breedingmarine birds to oil spills:guillemot and 12 Biol. Studies: 1-258. kittiwake populations on the Pribilof Islandsß ß--., & W. H. DRURY. 1981. Breeding dis- Bering Sea. J. App1. Ecol. 19: 1-31. tribution and reproductive biology of marine FURNESS,R. W. !978. Energy requirements of sea- birds in the eastern Bering Sea. Pp. 649-688 in bird communities:a bioenergeticsmodel. J. Anim. The easternBering SeaShelf: oceanographyand Ecol. 47: 39-53. resourcesßvol. 2 (D. W. Hood and J. A. Calderß ß& T. R. BIRKHF•D.!984. Seabirdcolony dis- Eds.). Washington, D.C.ß Natl. Oceanic Atmo- tributions suggestcompetition for food supplies spheric Admin.ß Office of Marine As- during the breedingseason. Nature (London)331: sessment. 655-656. JARVIS,M. J.F. !974. The ecologicalsignificance of ß & J. COOPER. 1982. Interactions between clutch size in the South African gannet [Sulaca- breeding seabirdsand pelagic fish populations pensis(Lichtenstein)]. J. Anim. Ecol. 43: 1-18. in the southern Benguela region. Marine Ecol. JOHNSON,$. R., & G. C. WEST. 1975. Growth and Prog. Series 8: 243-250. developmentof heat regulation in nestlingsßand GASTON,A. J. In press. Developmentof the young metabolism of adult Common and Thick-billed in the Atlantic Alcidae. In The Atlantic Alcidae murres. Ornis Scandinavica 6: 109-!!5. (D. N. Nettleship and T. R. Birkhead,Eds.). Lon- LLOYD,C. S. !979. Factorsaffecting breeding of Ra- don and New Yorkß Academic Press. zorbills Alca torda on Skokholm. Ibis 12!: !65- ß G. CHAPDELAINE,& D. G. NOBLE. 1983. The 176. growth of Thick-billed Murre chicksat colonies MAHONEYß $. P., & W. THRELFALL. 1981. Notes on in Hudson Strait: inter- and intra-colony varia- the eggsßembryos and chick growth of Common tion. Can. J. Zool. 6!: 2465-2475. GuillemotsUria aalgein Newfoundland.Ibis 123: -, & D. N. NETTLESHIP. 198!. The Thick-billed 211-218. Murres on Prince LeopoldIsland--a study of the MAUNDERßJ. E., & W. THRELFALL. 1972. The breed- breeding biology of a colonialßhigh arctic sea- ing biology of the Black-leggedKittiwake in bird. Monogr. No. 6. OttawaßOntarioß Canadian Newfoundland. Auk 89: 789-816. Wildl. Serv. NETTLESHIP,D. N. 1972. Breeding successof the HARRISßM.P. 1982. Seasonalvariation in fledging Common Puffin (Fraterculaarctica L.) on different 314 HUNT,EPPLEY, AND SCHNEIDER [Auk, Vol. 103

at Great Island, Newfoundland. Ecol. Oak Ridge, Tennessee, U.S. Atomic Energy Monogr. 42: 239-268. Comm. NYSEWANDER,D. g., & D. B. BARBOUR. 1979. The TUCK,L. 1961. The Murres. Monogr. No. 1.'Ottawa, breedingbiology of marine birds associatedwith Canadian Wildl. Serv. Chiniak Bay, Kodiak Island. Environmental as- WHITTAM,T. S., & D. SIEGEL-CAUSEY.1981. Species sessment of the Alaskan Continental Shelf. An- interactions and community structure in Alas- nual reportsof principal investigators.Boulder, kan seabird colonies. Ecology 62: 1515-1524. Colorado, Natl. Oceanic Atmospheric Admin. Environ. Res. Lab. 2: 21-106. PEARSON,T.H. 1968. The feeding biology of seabird speciesbreeding on the , North- APPENDIX.Colony and populationsizes (no. of birds) umberland. J. Anim. Ecol. 37: 521-552. for coloniesused in analysis(Fig. 2). "+" indicates PERRINS,C. M., M.P. HARRIS, • C. K. BRITTON. 1973. speciesincluded in calculating"effective colony Survival of Manx ShearwatersPuffinus puffinus. size." BLK = Black-leggedKittiwake, CM = Com- Ibis 115: 535-548. mon Murre, TBM = Thick-billed Murre. Numbers PETERSEN,M. R., & M. J. SIGMAN. 1977. Population in p•rentheses refer to sources. dynamics and trophic relationships of marine birds in the Gulf of Alaska and southern Bering Colony and population Sea. Part XII, Field studiesat Cape Peirce, Alas- sizes ka-1976. Environmental assessment of the Alaskan Continental Shelf. Annual reports of A. St. Paul Island, Bering Sea 253,800 principal investigators.Boulder, Colorado,Natl. + Northern Fulmar 700 OceanicAtmospheric Admin. Environ. Res.Lab. (Fulmarusglacialis) 4: 633-693. Red-faced Cormorant 2,500 (Phalacrocoraxurile) SCHNEIDER,D., & G. L. HUNT,:JR. 1984. A compari- + Black-leggedKittiwake 31,000 son of seabird diets and foraging distribution (Rissatridactyla) around the Pribilof Islands.Pp. 86-95 in Marine + Red-legged Kittiwake 2,200 birds: their feeding ecology and commercial (R. brevirostris) fisheries relationships (D. N. Nettleship, G. A. + Common Murre 39,000 Sanger, and P. F. Springer, Eds.). Proc. Pacific (Uria aalge) Seabird Group Symp., Seattle, Washington, 5-8 + Thick-billed Murre 110,000 January1982. Special publication.Ottawa, On- (U. lornvia) Parakeet Auklet 34,000 tario, Canadian Wildl. Serv. ( Cyclorrhynchuspsittacula) SOKAL,R. R., & F. J. ROHLF. 1969. Biometry. San Crested Auklet 6,000 Francisco, W. H. Freeman and Co. (Aethia cristatella) SOWLS,A. L., S. A. HATCH, & C. J. LENSINK. 1978. Least Auklet 23,000 Catalog of Alaskan seabird colonies.FWS/OBS (A. pusilia) + Horned Puffin 4,400 78/78. Washington, D.C., U.S. Fish Wildl. Serv. (Fratercula corniculata) SPRINGER,A., & D. ROSENEAU.1978. Ecologicalstud- + Tufted Puffin 1,000 ies of colonial seabirdsat Cape Thompsonand (F. cirrhata) Cape Lisburne, Alaska. Environmental assess- ment of the Alaskan Continental Shelf. Annual Source:SowIs et al. 1978 (map 38, site 2); repro- ductive measures from Hunt et al. 1982 (BLK, reports of principal investigators.Boulder, Col- CM, TBM) orado, Natl. Oceanic Atmospheric Admin. En- viron. Res. Lab. 2.' 839-960. B. St. GeorgeIsland, Bering Sea 2,519,000 , --, & M. JOHNSON. 1979. Ecological + Northern Fulmar 70,000 studies of colonial seabirdsat Cape Thompson Red-faced Cormorant 5,000 and Cape Lisburne, Alaska. Environmentalas- + Black-leggedKittiwake 72,000 sessment of the Alaskan Continental Shelf. An- + Red-legged Kittiwake 220,000 + Common Murre 190,000 nual reportsof principal investigators.Boulder, + Thick-billed Murre 1,500,000 Colorado, Natl. Oceanic Atmospheric Admin. Parakeet Auklet 150,000 Environ. Res. Lab. 2: 516-574. Crested Auklet 28,000 SQUIBB,g., & G. L. HUNT, JR. 1983. A comparisonof Least Auklet 250,000 nesting-ledgesused by seabirdson St. George + Horned Puffin 28,000 Island. Ecology64: 727-734. + Tufted Puffin 6,000 SWARTZ,L. G. 1966. Sea-cliff birds. Pp. 611-678 in Source:Sowls et al. 1978 (map 38, site 1); repro- Environment of the Cape Thompson region, ductive measures from Hunt et al. 1982 (BLK, Alaska(N.J. Wilimovskyand J. N. Wolfe, Eds.). CM, TBM) April1986] ReproductivePerformance ofSeabirds 315

APPENDIX. Continued. APPENDIX. Continued.

Colony and Colony and population population sizes sizes

C. Skomer Island (including Skok- H. CoburgIsland, eastern holm and Middleholm colo- Canadian Arctic 380,350 nies), Irish Sea 331,732 + Glaucous-wingedGull 150(1) + Manx Shearwater 260,000 (1, 2) + Black-leggedKittiwake 60,000 (2) (Puffinuspuffinus) + Thick-billed Murre 320,000 (2) + Northern Fulmar 224 (4) + Black Guillemot 200 (I) Storm-Petrels 12,920 (3) Sources:(I) Birkhead and Nettleship 1981, (2) Gas- Shags 30 (4) Cormorants 28 (4) ton and Nettleship 1981;reproductive measures + Great Black-backed Gull 314 (4) from Birkheadand Nettleship 1981 (TBM) (Larus marinus) + LesserBlack-backed Gull 20,000 (4) I. North Shields, North Sea (L. fuscus) + Black-leggedKittiwake (1963) 150b + Herring Gull 7,600 (4) (1983) 200b (L. argentatus) + Black-leggedKittiwake 5,000 (4) Source:Coulson and Thomas 1985;reproductive + 4,296 (3, 4) measures from Coulson and White 1958, 1961 (Alca torda) (BLK); Coulson and Thomas 1985 (BLK) + Common Murre 5,320 (3, 4) + 16,000 (4) (Fratercula arctica) J. Bluff, Norton Sound, Bering Sea 53,834 PelagicCormorant 518 Sources:(I) Corkhill 1973b, (2) Perrins et al. 1973, (Phalacrocoraxpelagicus) (3) Cramp et al. 1974, (4) T. R. Birkhead in lift.; + Glaucous-wingedGull 274 reproductivemeasures from Birkhead 1977(CM), + Black-leggedKittiwake 7,550 Birkhead and Hudson 1977 (CM) + Common Murre 41,800 + Thick-billed Murre 400 D. Farne Islands, North Sea 50,000 • Parakeet Auklet 65 Source:Cramp et al. 1974; reproductive measures + Horned Puffin 3,186 from Cullen 1957 (BLK), Pearson 1968 (BLK, CM) + Tufted Puffin 41

E. Akpatok Island, eastern Canadian Source:Sowls et al. 1978(map 95, sites2-6); repro- Arctic 840,000 ductive measuresfrom Drury et al. 1981 (BLK, CM) + Thick-billed Murre 840,000 Source:A. J. Gastonin litt.; reproductivemeasures from Gaston et al. 1983 (TBM) K. Cape Lisburne, Chukchi Sea 126,768 PelagicCormorant 78 F. Cape Hay, Bylot Island, eastern + Glaucous-wingedGull 50 Canadian Arctic 320,350 + Black-leggedKittiwake 25,000 + Glaucous-wingedGull 150 (I) + Common Murre 70,000 (Larusglaucescens) + Thick-billed Murre 30,000 + Black-leggedKittiwake 40,000(2) + Black Guillemot 170 + Thick-billed Murre 280,000 (2) + Horned Puffin 1,450 + Black Guillemot 200 (I) + Tufted Puffin 20 (Cepphusgrylle) Source:Sowls et al. 1978(map 128,site 17);repro- Sources:(1) Birkheadand Nettleship 1981,(2) Gas- ductivemeasures from Springerand Roseneau ton and Nettleship 1981;reproductive measures 1978 (BLK), Springer et al. 1979 (BLK) from Birkhead and Nettleship 1981 (TBM) G. Prince Leopold Island, eastern L. Cape Thompson,Chukchi Sea 417,695 Canadian Arctic 362,400 PelagicCormorant 46 + Northern Fulmar 124,000 + Glaucous-wingedGull 300 + Black-leggedKittiwake 26,500 + Glaucous-wingedGull 400 + Common Murre 155,719 c + Black-leggedKittiwake 58,000 + Thick-billed Murre 233,578c + Thick-billed Murre 172,000 + Black Guillemot 4 + Black Guillemot 8,000 + Pigeon Guillemot 14 Source:Gaston and Nettleship 1981; reproductive (Cepphuscolumba) measuresfrom Gastonand Nettleship1981 (TBM) + Horned Puffin 1,494 316 HUNT,EPPLEY, AND SCHNEIDER [Auk, Vol. 103

APPENDIX. Continued. APPENDIX. Continued.

Colony and Colony and population population sizes sizes

Source:SowIs et al. 1978 (map 129, sites 1-5); re- P. Cape Peirce and nearby colonies, productive measures from Swartz 1966 (CM, Bristol Bay, Bering Sea 576,809 TBM), Springer and Roseneau 1978 (BLK), Cormorants 2,315 (I, 2) Springer et al. 1979 (BLK) + Glaucous-wingedGull 5,715 (1, 2) + Black-leggedKittiwake 100,460 (I, 2) M. Kulichoff Island and nearby colo- + Common Murre 381,590 (1, 2) nies in Kodiak Bay, Kodiak Is- + Pigeon Guillemot 300 (1, 2) land, North Pacific 25,942 Parakeet Auklet 100 (1, 2) Pelagic Cormorant 1,377 + Horned Puffin 1,184 (1, 2) Red-faced Cormorant 738 + Tufted Puffin 85,145 (1, 2) + Glaucous(Larus hyperboreus) and Sources:(I) SowIs et al. 1978 (map 39, sites 3-11), Glaucous-wingedgulls 2,428 (2) S. R. Johnsonpers. comm. (revised estimate + Mew Gull 450 for Cape Peirce); reproductive measuresfrom (L. canus) Petersenand Sigman 1977 (BLK) + Black-leggedKittiwake 7,477 + 881 Q. Dunbar, North Sea 450 + Common Murre 480 + Black-leggedKittiwake 450b + Pigeon Guillemot 314 + Horned Puffin 441 Source:Coulson 1963; reproductive measures from + Tufted Puffin 11,386 Coulson and White 1961 (BLK)

Source:SowIs et al. 1978 (map 34, sites 15-18, 22, R. Brownsman, North Sea 50,000 (2) 47, 85-90, 99-101); reproductive measuresfrom Nysewanderand Barbour1979 (BLK) + Black-leggedKittiwake I0,000 (1) Sources:(1) Coulson 1963, (2) Cramp et al. 1974; N. Sitkalidak Strait, Kodiak Island, reproductivemeasures from Coulsonand White North Pacific 22,743 1961 (BLK) PelagicCormorant 252 Red-faced Cormorant 137 S. St. Abbs, North Sea 50,000(2) + Glaucous-wingedGull 940 + Black-leggedKittiwake 13,000(1) + Mew Gull 20 Sources:(1) Coulson 1963, (2) Cramp et al. 1974; + Black-leggedKittiwake 4,766 reproductive measuresfrom Coulson and White + Terns 2,340 1961 (BLK) + Pigeon Guillemot 520 + Horned Puffin 184 T. Middleton Island, North Pacific 167,935 + Tufted Puffin 13,584 PelagicCormorant 4,682 Source: Baird and Hatch 1979; reproductive mea- + Glaucous-wingedGull 1,140 sures from Baird and Hatch 1979 (BLK) + Black-leggedKittiwake 150,494 + Common Murre 6,596 + Thick-billed Murre 207 O. Gull Island and nearby colonies + Rhinoceros Auklet 1,316 in Witless Bay (Green, Pebble, and Great islands), North Atlan- (Cerorhincamonocerata) + Tufted Puffin 3,500 tic 2,691,210 Leach's Storm-Petrel 2,000,000 (2) Source: SowIs et al. 1978 (map 48, site 1); repro- (Oceanodromaleucorhoa) ductive measures from Hatch et al. 1979 (BLK, + Northern Fulmar 12 (1) CM, TBM) Double-crested Cormorant 500 (1) (Phalacrocoraxauritus) U. Runde, North Sea 278,588 + Black-leggedKittiwake 83,070 (I) + Northern Canner 988 (1) + Razorbill 640 (1) ( Sula bassanus) + Common Murre 154,960 (I) + Black-leggedKittiwake 200,000(2) + Thick-billed Murre 1,200 (1) + Razorbill 5,600 (1) + Atlantic Puffin 480,840 (1) + Common Murre 12,000(1) Sources: (1) Brown et al. 1975, (2) A. J. Gaston in + Atlantic Puffin 60,000(1) litt.; reproductive measuresfrom Maunder and Sources:(I) Brun 1979, (2) Barrett and Runde 1980; Threlfall 1972(BLK), Mahoney and Threlfall 1981 reproductive measuresfrom Barrett and Runde (CM) 1980 (BLK) April 1986] ReproductivePerformance ofSeabirds 317

APPENDIX. Continued. APPENDIX. Continued.

Colony and Colony and population population sizes sizes

V. Stora Karlso, 17,100 Z. Kongkok Bay and nearby colo- + Lesser Black-backed Gull 1,300 nies, St. Lawrence Island, Ber- + Herring Gull 600 ing Sea 763,050 + Razorbill 2,400 Pelagic Cormorant 300 + Common Murre 12,800 + Black-leggedKittiwake 1,800 + Murres 216,000 e Source:Hedgren and Linnman 1979; reproductive Parakeet Auklet 1,600 measuresfrom Hedgren and Linnman 1979(CM); Crested Auklet 181,000 Hedgren 1980, 1981 (CM) Least Auklet 361,000 W. Hekkingen, North Sea ? + Horned Puffin 600 + Tufted Puffin 750 + Black-leggedKittiwake 520 Source:Barrett and Runde 1980;reproductive mea- Source:Sowls et al. 1978 (map 93, sites 1, 12); re- sures from Barrett and Runde 1980 (BLK) productivemeasures from Johnsonand West 1975 (CM, TBM) X. DiggesSound (including Cape Wolstenholme), eastern Canadi- A1. CommanderIslands, Bering Sea ? an Arctic 607,000 + Black-leggedKittiwake 12,000 + Thick-billed Murre 600,000 + Black Guillemot 5,000 Source:Firsova 1978; reproductive measuresfrom + Arctic 1,000 a Firsova 1978 (BLK) (Sternaparadisaea) aColony size 10,000-100,000; no population esti- Source:A. J. Gaston in litt.; reproductive mea- mates. sures from Gaston et al. 1983 (TBM) b Population estimatesbased on the number of ac- tive , rather than the number of birds on the Y. Hantzsch Island, eastern colony. Canadian Arctic 110,000 ½Obtained using SowIs et al.'s (1978) figure for + Black-leggedKittiwake 10,000 murres and Swartz's (1966) estimate of 60% Thick- + Thick-billed Murre 100,000 billed Murres. a Gastonreports "several hundred pair"; assume500 Source:A. J. Gastonin litt.; reproductivemeasures pairs here. from Gaston et al. 1983 (TBM) e Assume 50% Thick-billed Murres.