Common Murre •.• Thick-Billed Murre

j. Field Ornithol., 54(3):266-274

THE FLEDGING OF COMMON AND THICK-BILLED MURRES ON MIDDLETON ISLAND, ALASKA

BY SCOTT A. HATCH

Three speciesof alcids,Common and Thick-billed murres (Uria aalge and U. lornvia)and the Razorbill (Alca torda),have post-hatchingdevelopmental patterns intermediate to precocialand semi-precocialmodes (Sealy1973). The youngleave their cliff nestsites at aboutone quarter of adult weight and completetheir growth at sea.At departure, an event here looselyreferred to as "fledging," neither primary nor secondary flight feathersare grown, but well-developedwing covertsenable lim- ited, descendingflight. The adaptivesignificance of thispattern maybe that leadingthe young to distantfeeding areasis more efficientthan lengthy foraging flights by adultsonce the chicks'energetic requirements exceed some critical level (Sealy 1973, Birkhead 1977). The risk to predation is probably greater in exposednest sitesthan at sea, contributing further to the selectiveadvantage of earlyfledging (Cody 1971, Birkhead1977). Given these constraints,however, larger chickswould be expected to better survivethe rigorsof fledging,increased activity at sea,and the vagaries of weather. Hedgren (1981) analyzed278 recoveriesof CommonMurres banded as fledglingsand found no significantrelationship between fledging weight and subsequentsurvival. This result is paradoxicalin view of a strong expectationto the contrary and evidencethat such an effect occursin other speciesof birds (Perrins 1965, Perrinset al. 1973, O'Con- ner 1976). Hedgren suggestedthe nestlingperiod of murres,averaging about3 weeks,is determinednot by a thresholdin bodysize, but by the relativelyconstant time requiredto completefeather growth.Birkhead (1977) alsoemphasized the need for chicksto attain a critical weight: wing-arearatio prior to fledging. Clearly, however,body weight and feather developmentare not mutuallyexclusive factors affecting fledg- ling survival. Murres breeding on Middleton Island, Alaska use nest siteslocated sofar from the water'sedge that direct flightsto the seaby the fledglings are impossible.In 1978, I capturednearly 400 fledglingsas they made their wayoverland to the sea.In thispaper I analyzemensural data for thesebirds with a viewto testingthe abovehypotheses regarding optimal fledging condition. My data also document population changesand breedingphenology of murres in a region for which there is little pub- lished information.

STUDY AREA AND METHODS Middleton Island is in the north-central Gulf of Alaska about 115 km from the mainland and 18 km from the edge of the continental shelf

266 Vol.54, •o. • FledgingofMurres in Alaska [267

,, I 'L,..,• Alaska \ /I ,//••',

'.,--.....'"'-'-'.... ,'// ///

Present low water ' '

•-'•, reefs ?'- I km

F•cuRE1. Map of MiddletonIsland showing changes in the shorelineand the distribution of murres in 1978. CM, Common Murres; TBM, Thick-billed Murres.

(Fig. 1). The islandis generallyflat, and reachesa maximum elevation of about 40 m on its southwestside. The Alaskan earthquakeof 1964 raisedthe islandabout 4.5 m, exposinglarge areasof previouslysub- merged land. On the east, south, and southwestthe distancebetween the sea cliffs and the present high water mark averagesabout 400 m. The intertidal zone extends another 200 to 1200 m seaward. Most murres nested near the top of a steep cliff surrounding the southernthird of the island.Nesting ledges did not exceedabout 35 m in height. The largestgroup of Common Murres, designatedthe "main colony," nestedon a broad ledge only 10-15 m high but 500 m from the high water level. Flatsbelow the cliffsconsisted of marshyground with a scatteringof large bouldersand numerousshallow ponds of fresh or brackish water. A censusof murres was carried out on 26 July when all birds were counted with a spotting scopefrom the flats. The proportions of the two speciesin the populationwere estimatedfrom the ratio of Common to Thick-billed murres in the population of chicksleaving the cliffs in August. 268] s.A. Hatch j. FieldOrn,thol. Summer 1983

Chicksfrequently did not completethe journey to seaon the same eveningthey left the cliffs,but spentone or moreof the followingdays accompaniedby adultsin the ponds.Chicks were capturedby hand duringdaily searches of the pondsbetween 26July and 16 August.Wing chord wasmeasured to the nearestmm with a stoppedruler; weight wasdetermined to within 1 g with a 300 g Pesolascale. All chickswere marked with U.S. Fish and Wildlife Servicemetal leg bandsat first capture,which permitted me to separaterecaptured chicks from those newlyarrived in the pondseach day. Everychick present in the ponds was captured each day, and the measurementof weight was repeated on recaptured chicks.

RESULTS AND DISCUSSION Censusand populationchange.--A total of 6803 murres was counted in the census.This figure agreeswith independentcounts by Gouldand Zabloudil,and Gouldand Nysewanderin 1981 and 1982, respectively (P. J. Gould, pers. comm.). Southern et al. (1965) showedthat the pro- portion of murrespresent on ledgesat any time during incubationand broodingis about 60% of the total population(including both breeders and nonbreedingnest-site holders). Extensivecounts at the Semidi Is- lands, Alaska (Hatch, unpubl• data) substantiatethis value as a conser- vativeadjustment for nest-siteattendance. Thus, the total population on MiddletonIsland in 1978 wasabout 11,000 birds(Fig. 1). Thick-billedMurres occurredonly north of the main colonyon the westside of the island.Here, theymade up about7.4% of the population, asestimated from the numberof Thick-billed Murres among311 chicks capturedin the area during fledging.I assumethe two specieshad similar nestingsuccess. The ratio agreeswith my general impressionfrom ob- servationsof birds on the ledges.Thick-billed Murres thus made up only 3% of the censustotal, or about 350 birds. Rausch(1958) visited Middleton Island in 1956 and found a population of only about 400 murres, mostlyThick-billed Murres. Thus, although the population of Thick-bills has changed little, Common Murres increasedgreatly between 1956 and 1978. The increaseis all the more remarkablein view of physicalchanges brought about by the 1964 earthquakewhich might havebeen expectedto discouragemurres from nestingon Middleton Island. The changein numbersof murres was paralleled by large increasesin the populationsof Black-legged Kittiwakes(Rissa tridactyla) and PelagicCormorants (Phalacrocorax pe- lagicus)(Hatch, unpubl. data). Timingoffledging.--The distribution of fledgingbetween 26 July and 16 Augustwas approximately normal, exceptfor a conspicuousdecline in the number of chicksleaving the cliffson 31 July and 1 August(Fig. 2). The lull occurredduring an unusualspell of foggyweather, although suchconditions might have been expectedto have the oppositeeffect. Peak numbersof birds left the cliffsas soonas the fog lifted. A few chicksprobably fledged before daily observationswere begun. vo•.54, No. • Fledgingof Murres in Alaska [269

50 Common Murres (exceptmain colony)

40 Thick-billed Murres Fog Common Murres (maincolony) '• 50 o

'" 20

? I •5 50 5 July August FIGURE 2. Distributionof fledgingdates of murres on Middleton Island in 1978.

On 27 May severalhundred murres were flushed from ledgesand only 3 eggswere present.This date probablymarked the commencementof egg-laying.If an incubationperiod of 33 daysand a nestlingperiod of 21 daysare assumed(Tuck 1960, Hedgren and Linnman 1979), these young shouldhave fledged about 20 July. Back-calculatingthe latest fledgingdates, I estimatethe lasteggs were laid about 23 June. There wasno discernibledifference between species in breedingphenology.The fledgingof CommonMurres in the main colony,however, seemedto be more synchronousthan elsewhereon the island. There was also evidencethat egg-layingmay have occurred later within the main colony(see below). Turr•overand survival in po•ds.--Lacking information on rates of breedingsuccess or the total productionof chicks,I cannotestimate the proportionof fledglingsthat remainedin the pondslong enoughto be banded.There islittle question,however, that the majorityof fledglings of both speciesreached the seawithin hoursof leavingthe cliff and were thereby excludedfrom this study. Thick-billedMurres showeda greatertendency to linger in the ponds than did Common Murres. More than 70% of Thick-billed Murres that remainedin the pondslong enoughto be bandedstayed at leastanother full day; 23c/cstill remainedafter 3 days(Fig. 3). By comparison,only 24% of CommonMurres were recapturedone or more times. 270] S.A.Hatch j. FieldOmithal. Summer 1983

Common(rl=352) Murre •.•Thick-billed (n = 22) Murre

5O i i

No. Days After First Capture FmURE 3. Length of residencyand mortalityof chicksin pondsafter fledging.

Most chicksreceived no food while they stayedin the ponds.They lost weight at a mean rate of 17.7 g/day (samplesfor both species combined)and facedan increasedprobability of deatheach day. Of 374 chicksbanded on or before 12 August, 18% were later recovereddead. In contrast,Thick-billed Murres had cumulativemortality of nearly50% (Fig. 3). These data suggestThick-billed Murres are behaviorallyless capableof dealing with the unusualcircumstances that have existedon Middleton Island sincethe earthquake.Possibly this is a contributing factor in their failure to increase their numbers. A few chickswere fed while in the pondsand surviveda week or more in fresh water, either maintainingweight or showinglimited gl*owth. An adult wasobserved delivering a meal to one suchchick. This seemed to be a learnedbehavioral pattern acquiredby only a few adults.At the lastvisit on 16 August, severalchicks that had spentmore than a week in one pond were alive and healthy. Predation by gulls is frequently cited as a major causeof mortality amongfledgling murres (Tuck 1960, Greenwood1964, Williams1975). Williams(1975) found this risk wassubstantially increased when access to the sea was hampered by difficult terrain. Some 1400 Glaucous- wingedGulls (Larus glaucescens) inhabited Middleton Island in 1978, yet thesebirds were notablyindifferent toward murre chicksunder all cir- cumstancesobserved. Only two murre chickcarcasses were encountered that appeared to have been partially eaten by gulls,and these may have Vol.54, No. 3 FledgingofMurres in Alaska [27 1

T^BLE 1. Measurementsof Common and Thick-billed murres at fledging on Middleton Island, Alaska.

Weight Wing Speciesand area (g) (mm) Common Murre 2 207.8 74.3 (exceptmain colony) SD 27.62 8.05 (n -- 288) Range 128-310 54-104 Common Murre • 190.7 68.4 (maincolony) SD 19.56 6.86 (n -- 86) Range 141-231 50-91 All Common Murres • 203.8 72.9 (n -- 374) SD 26.51 8.17 Range 128-310 54-104 Thick-billed Murre • 200.7 80.5 (n = 23) SD 35.56 7.84 Range 125-292 62-101

been scavengedafter death from other causes.Observed mortality of murre chicksseemed to result from the depletion of energy reserves and exposure.Chicks were often found in a lethargic and probably hypothermiccondition shortly before they died. To test the possibilitythat fledgingweight affected survival in the ponds,I calculateda regressionof initial weight(X) and the numberof dayssurvived (Y) for 52 CommonMurres that died in the ponds:Y = - 1.89 + .022(X). This relationshipwas highly significant(P < .001; r = .54). The regressioncoefficient of 0.022 indicatesthat chickssurvived withoutfood about 1 additionalday for each50 g incrementin fledging weight.With a sampleof only 9 chicks,the relationshipfor Thick-billed Murres, although similar, was nonsignificant. Johnsonand West (1975) found that resistanceto hypothermia in murres is achievedmainly by a high capacityfor metabolicheat pro- duction.Consequently, murres have a large daily energyrequirement. Althoughatypical, the situationon MiddletonIsland simulateswhat mayoccur when murres encounter untimely storms and poor foraging conditionssoon after fledging. I believe my data demonstratea real advantageof increasedfledging weight which, however, may only rarely be of critical importance. Fledgingcondition: means and variability.--Upon leaving the cliffs,374 CommonMurres ranged in weightfrom 128 to 310 g (• = 204 g), while 23 Thick-billed Murres rangedfrom 125 to 292 g (• = 201 g; Table 1). These valuesare at the low end of the range of meansdetermined at various locations in the North Pacific and North Atlantic Oceans (cf. datasummarized by Tuck 1960and Hedgren and Linnman 1979). Pos- siblythe chicksobtained in the pondswere a relativelyundernourished group.I think this is unlikelybecause all the chicksappeared healthy 272] S.A.Hatch J.Field Ornithol. Summer 1983

Predicted All Common Murres Thick-billed Murre VwT VwT VwT

Vw, Vw, Vw, Vw, NS Vw,

Common Murre Common Murre (exceptmoin colony) (moincolony) VwT VWT .oo/o, ,o/\s

Vw, ,05 -- Vw, VwL ,05 Vw, FIGURE4. Relativevariability in sizecharacteristics among murres at fiedging.VWT, Vw•, and VwLare coefficientsof variationfor weight,wing-length, and wing-loading,respectively.Arrows point from lowerto highervalues. Numbers are the probability levelsindicated by one-tailedtests. Sample sizes as in Table 1. and vigorouswhen they were first captured.Younger chicks, however, may well have been more inclinedto stayin the ponds. The speciesdid not differ significantlyin fiedgingweight, but Thick- billed Murres had longer wings(P < .001, two-tailedt-test). Adult Thick- billed Murres studiedat CapeThompson, Alaska averaged significantly lighter and had longer wingsthan Common Murres (Swartz 1966). Hedgren(1979, alsosee Hedgren and Linnman 1979)found a marked seasonaldecline in the fiedgingweight of CommonMurres, but this was not observedon Middleton Island.There were no significantdifferences amongchicks fledged during early (26 July-1 August, n = 73), middle (2-8 August, n = 165), or late (9-16 August, n = 51) portions of the season.However, Common Murres from the main colony averaged smallerin both weight and wing length than fledglingscaptured to the north (P < .001 in both instances, t-tests). The smaller•' chicks either grew more slowlyor fledgedat an earlier age. If the latter wastrue it would indicate a premium on fiedging during a particular interval, al- thoughHedgren (1981) wasunable to showsuch an effectby an analysis of band recoveries.Possibly the age and breedingexperience of adults differed betweenareas, resulting in later breeding times and/or poor qualityparental care. Suchspatial variability in breedingperformance associatedwith rapid expansionof the colonywas indicated in a study of the Black-leggedKittiwake on Middleton Island(Hatch, unpubl.data). The initial weightsof Common Murres that died in the pondsaver- aged significantlylower than thosethat eventuallymade it to sea(199 vs. 210 g, P < .005, one-tailedt-test). This resultreinforces my conclu- Vol.54, No. 3 FtedgingofMurres in Alaska [273 sionfrom the regressionof fiedgingweight and longevityfor chicksthat died: fledgingweight affectschances for survival. An alternative,or additional, factor that may determine the length of the nestling period in murres is the developmentof an adequate capabilityfor flight. On this hypothesisI would expect wing length to showless variability at fledgingthan weight. Moreover, if wing-loading is the prime consideration,the ratio of weight to wing length (an index to wing-loading)should be lessvariable than either characteralone. An appropriate test of these predictionsis a comparisonof coefficientsof variation (Sokal and Braumann 1980). I verified the absenceofskewness in the distributionsof all three charactersfirst, becausesignificance tests for coefficientsof variation are highly sensitiveto skewnessin the un- derlying data (Sokal and Braumann, loc. cit.). Predicted and observed resultsof theseanalyses are summarizedby speciesand area in Fig. 4. With two minor, nonsignificantexceptions, the expectedrelationships were confirmed:the nestlingperiod of murres would seemto be under selectionpressure with respectto both fledgingweight and the timing of feather development.

SUMMARY A 16-fold increasein the population of murres on Middleton Island occurredin 22 yearsor fewer. The breeding schedulesof Common and Thick-billed murreswere similar in 1978, with young of both species leavingthe cliffsbetween about 20July and 16 August.Chicks frequently spentone or more daysin fresh water pondsafter fledging.Considerable mortality occurred in this situation, especiallyamong Thick-billed Murres.That fledgingweight may affect the survivalof newly-fledged chickswas indicatedtwo ways:(1) fledging weight was higher among chicksthat madeit to seathan in chicksthat remainedin the pondsand died; (2) the number of dayssurvived by birds of the latter group was positivelycorrelated with their fledging weights.The nestlingperiod seemsto be further governedby feather developmentrelative to body weight, sincewing length and wing-loadingare more constantamong fledglingsthan weight.

ACKNOWLEDGMENTS I thank T. W. Pearsonfor assistancein the field, and C. J. Lensink and P. J. Gould for critically reading the manuscript.The work on Middleton Islandwas supported by the AlaskanOuter ContinentalShelf EnvironmentalAssessment Program administered by the U.S. Bureau of Land Management and National Oceanic and Atmospheric Admin- istration.

LITERATURE CITED

BIRKHEAD,T. R. 1977. Adaptive significanceof the nestlingperiod of GuillemotsUria aalge.Ibis 119:544-549. 274] s.A. Hatch j. FieldOrnithol. Summer 1983

COPY,M. L. 1971ß Ecologicalaspects of reproductionßPp. 461-512, in D. S. Farner and J. R. King (eds.),Avian Biology,Vol. 1. AcademicPress, New York. GREENWOOD,J. 1964. The fledgingof the GuillemotUria aalgewith noteson the Razorbill Alca torda. Ibis 106:469-481ß HEDCREN,S. 1979ß Seasonalvariation in fledging weight of GuillemotsUria aalge.Ibis 121:356-361. ß 1981ß Effectsof fledging weight and time of fledgingon survivalof Guillemot Uria aalgechicksß Ornis Scand. 12:51-54. , ANDA. LINNMAN.1979. Growth of Guillemot Uria aalgechicks in relation to time of hatching.Ornis Scand. 10:29-36. JoHnson,S. R., A•D G. C. WEST.1975. Growth and developmentof heat regulationin nestlings,and metabolismof adult Commonand Thick-billed murres. Ornis Scand. 6:109-115. O'Co•ER, R.J. 1976. Weightand body composition in nestlingBlue Tits Paruscaeruleus. Ibis 118:108-112. PERR•S,C. M. 1965. Populationfluctuations and clutchsize in the Great Tit, Parusmajor L.J. Anim. Ecol.34:601-647. , M.P. HARRIS,AND C. K. BRITTON.1973. Survivalof Manx ShearwatersPuffinus puffinus.Ibis 115:535-549. RAUSCH,R. 1958. The occurrence and distribution of birds on Middleton Island, Alaska. Condor 60:227-242. SEALY,S. G. 1973. Adaptivesignificance of post-hatchingdevelopmental patterns and growth rates in the alcidae.Ornis Scand.4:113-121. SOKAL,R. R., ANDC. A. BRAUMANN.1980. Significancetests for coefficientsof variation and variabilityprofiles. Syst. Zool. 29:50-66. SOt•rHER•, H. N., R. CARRICK,A•D W. G. PO-rTER. 1965. The natural history of a populationof Guillemots(Uria aalgePont.). J. Anim. Ecol. 34:649-665. SWAR-rz,L. G. 1966. Sea-cliffbirds. Pp. 611-678, in N.J. Wilimovskyand J. N. Wolfe (eds.),Environment of the CapeThompson region Alaska. U.S. AtomicEnergy Comm., Oak Ridge, Tenn. TucK, L. M. 1960. The tourres. Canadian Wildlife Series: 1. Queen's Printer, Ottawa. W•LLIAMS,A.J. 1975. Guillemotfledging and predationon Bear Island.Ornis Scand.6: 117-124. U.S. Fish and Wildlife Service,1011 East Tudor Rd., Anchorage,Alaska 99503. Received9 Sept. 1982; accepted5 May 1983.