WESTERN BIRDS Volume 15, Number 4, 1984 BREEDING PHENOLOGY AND MID-SEASONAL SOCIAL BEHAVIOR OF THE SOOTY GUILLEMOT ON TEUR! ISLAND, JAPAN ASA C. THORESEN• Biology DepartmenL Andrews University,Berrien Springs, Michigan 49104 The breeding biology of the genus Cepphus (Alcidae) is representedin literaturefor two of the three species:Cepphus grylle, the Black Guillemot and Cepphus columba, the Pigeon Guillemot (Asbirk 1978, 1979a and b; Cairns 1978, 1979, 1980, 1981: Drent 1965: Hyde 1936, 1937; Preston 1968: Storer 1952: Thoresen and Booth 1958; Winn 1950). Notations within larger compilations (Dement'ev and Gladkov 1951, Kozlova 1957) and a short paper by Nazarov and Labzyuk (1972) have been the only reportspublished on the habitsof Cepphuscarbo, the Sooty (or Spectacled) Guillemot.Austin and Kuroda (1953) recordeda populationof at least7000 Sooty Guillemotson Teuri Island, Japan, in 1949, which was at that time the largestknown aggregationof the genusanywhere in the world. Unfortunate- ly, this figure is difficult to substantiateand the present number on Teuri Island does not exceed 400 birds, includingnon-breeders (Environmental Agency 1973). Colonies twice the size inhabit Soviet islandsto the north (Nazarovand Labzyuk1972). I campedon Teuri Islandin June and July 1981, to observethe breedinghabits of this little studiedspecies. All three speciesof Cepphusnest as individualpairs, in smallgroups, or in largergroups -- up to 10,000 pairsfor the BlackGuillemot (Nettleship 1974) -- accordingto the availabilityof nestingcavities and abundanceof food sup- ply. The Sooty Guillemotranges from the coastsof northernJapan, Korea, and southern Kuriles to the shores of the Okhotsk Sea (Dement'ev and Gladkov 1951). The bird differsfrom the other two speciesin beingslightly larger,lacking white wing patches, and possessingwhite eyelids which merge with white facialplumage. As in the other two species,the Sooty has con- spicuouslyred feet and legs.The interiorlining of the mouth is fleshpink as opposed to the brightcoral red of the Black and Pigeon guillemots. WesTern Birds 15:145-160. 1984 145 SOOTY GUILLEMOT STUDY AREA AND METHODS Teuri Island (lat. 44ø4'N, long. 141ø3'E), is one of two islandslocated ap- proximately 38 km off the northwestcoast of Haboro, Hokkaido, Japan. Teuri is famous in Japan as a National Monument for seabirdsand is a well- known tourist attraction (Environmental Agency 1973). Teuri Island is approximately5.5 km2 and has almost 12 km of coastline, one third of which is suitablefor breedingseabirds. The islandrises gently at the north end from east to west and more abruptly at the south end to high points of approximately 100 m. The rock is composed of volcanicbreccia overlain with ash conglomerates.Several rocky stacksalong the western shoreline also provide nestingplaces for birds. A village of just over 1000 persons is located at the sheltered northeasternend of the island. The sea was remarkablycalm during June and July althougha few wet, foggy and windy days impeded observations.Air temperaturesvaried be- tween 16 and 20 ø C, and the sea temperaturesat shore were just a degree or two belowair temperature.Tidal effectwas practicallynil, with a differenceof lessthan 1 m between high and low tides throughoutJune and July. Teuri Island is the site of the largestknown colony of RhinocerosAuklets (Cerorhinca monocerata) where a minimum of 500,000 and a maximum estimation of 785,000 individuals breed (Environmental Agency 1973). Other breedingspecies include Black-tailedGull, Laru$ cra$$iro$tri$,40,000; Slaty-backedGull. Larus$chi$tisagu$. 400: Common Murre, Uria aalge. 700 to 800: Sooty Guillemot, Cepphu$ carbo, 380 to 400: and a few scattered Ancient Murrelets, $ynthliborarnphu$ antiquu$. (All figures represent individuals.) I camped on Teuri from 3 June to 31 July 1981, observingfor more than 700 hours. From within 25 to 50 m of the campsite 20 or more Sooty Guillemotscould be observed. An additional group of birds could be seen Figure1. Part of the studyarea on TeuriIsland, Japan. 146 SOOTY GUILLEMOT easilywith binocularsto the south.To the north, beyondrock piles.the remaining300 plus birdswere countedeach day shortlyafter dawn and at intervalsthroughout the day. Attendance counts were made by counting everyhour all birdswithin view of the campsitearea on the seaand on land near nestingsites. Locations of nest cavitieswere determinedby observing the movementsof the birdsto and from the cliffs.Sightings of birdscarrying fish were used to determine locations of nest sites in which chicks were present. A rock blind was constructedfrom which the entranceto eight nestsknown to containchicks could be seen. Among the boulderpiles at the baseof the cliff20 nestswere locatedbut only 7 of thesewere shallowenough to permit access to their contents. Binoculars,notebook. tape recorder.a 16 mm motion picturecamera and a 35 mm motor-driven camera were used for recordingbehavior. The early matingbehavior was entirely missed. nevertheless social activities continued throughoutJune and July. Figure 1 picturesthe campsiteand part of the observationarea on Teuri. Figure 2 showsfour adult birds. RESULTS AND DISCUSSION Breeding Chronology and Development of Young Storer (1952)indicated that the prenuptial (prealternate)molt of the Sooty Guillemot appeared to occur in January and February in northern Japan. This observationfits in well with the early onset of breeding activitieswhich take place on Teuri Island. Eggs were already hatching on 2 June 1981. On 5 June, five of seven accessiblenests contained eggs: three containedtwo eggsand two only one. Matutoshi Aotsuka. warden of birds on Teuri Island. informed me that the . .:: ... Figure 2. Adult Sooty Guillemots perched near a nestingarea One bird utters the alarm Scream from a resting position 147 SOOTY GUILLEMOT eggsusually hatched at aboutthe sametime everyyear and that, in 17 years of banding birds on Teuri, he had never found more than one Sooty Guillemot chickbeing fledged from a nest. Nazarov and Labzyuk (1972) also could find only one chick in each nest they examined. My observations showed that although two chicksmay hatch, only one fledges. In one nest the secondchick to hatch was found dead on the secondday with its head severelypecked. On 4 July 1981 the first fledgling was seen on the bay, where it was observeddaily until 20 July. Allowing 40 plus days for the nestlingstage (basedon recordsfrom three nests)and assumingthat the incubationperiod averaged 30 days, the first eggsof the Sooty Guillemot on Teuri probably were laid about 26 April and hatched 26 May. To the north Nazarov and Labzyuk (1972) found the earliesteggs on 8 May with the greatestnumber being laid after 20 May. Of a maximum population of about 400 individuals, no more than 200 were breedersin 1981. In otherwords, there may have been a maximumof 100 nestswith a lessernumber of pairs rearingyoung. Nestswere located under rock piles, in crevices,and under rocks higher on the slopes.Sixty percent of the nest sites, as determinedby observingbirds flying to them, were more than 20 m above sea level (see Figure 3). Nest siteswere often defendedlate in the seasonby adultswithout eggs or youngbeing raised in them. Preston (1968) noted this behavior also in the Black Guillemot on Kent Island in all five years of his study. Throughout June and July, I observeddaily 5 to 10 non-breederswhich were stillin mottled-greybelly plumage. These immature birds displayed with the other membersof the colony.Kozlova (1957) and Nazarovand Labzyuk (1972) have also noted that young birdsfrequently retain white featherslate into June. The eggs of the Sooty Guillemotsresemble in appearancethose of the other two species.The two eggsof a singleclutch are not alwaysmarked alike, a feature also noted in the Pigeon Guillemot (Thoresenand Booth 1958). However, Asbirk (1979b) commented that the two eggs from the sameclutch of DanishBlack Guillemots always have the sameground color and the same pattern of spots.Ten eggson Teuri averaged60.37 x 41.70 mm with a range of 57.60 - 63.80 x 40.3 - 43.8 mm. These were smaller than 14 eggsmeasured by Nazarovand Labzyuk(1972) who on more north- erly islandsfound a rangeof 61.1 - 66.8 x 41.1 - 45.2 mm. Nine eggsat late stagesof incubationhad an averageweight of 55.57 g with a range of 50.0 - 60.1 g. Chickswere fed at varyingperiods during the day. Early morningand late evening feedings were more frequent than midday feedingsin 20 nests observed.Three to eight feedingsper day, with an averageof five, were observedon four differentdays, from dawn until sunset.Small chickswere usuallyfed fish 4-6 cm long. Occasionallya fish, too large for a chickto swallow,was eitherleft at the nestsite or carriedaway againby the parent. The mostcommon fish seenbeing brought to the nestwere sandlance (Am- rnoclytessp.), rock blennies (Pholissp.) and small sculpins.Three 20 cm sandlance weighingbetween 28 and 29 were dropped at one nest. (A single 4.0 cm sand lance weighedonly 2.0 g). As is well known, Cepphusfeed 148 SOOTY GUILLEMOT upon practicallyany small fish they are capableof catching.For example, Follett and Ainley (1976), in a study of the Pigeon Guillemot in central California found representativesof 10 families of fish including 19 genera and 24 speciesto form the prey of that species.The Sooty Guillemotis pro- bably just as adaptablein its diet. The chicksof Sooty Guillemots,upon hatching,look just like the young chicksof the other two species.They have a full coveringof sooty-black down. The legs and feet are pink, turningblack in a day or two. The bill is also black with a prominentwhite egg-tooth on the top mandible,while at the tip of the lower mandible a smaller egg tooth is also present. These featuresmatch those of the other speciesof Cepphus(Sealy 1970). Both egg teeth graduallywear off, but in the three chicksobserved to fiedging,a rem- nant of the upper one remained up to the 40th day. A singlechick hatched with a body weightof lessthan 40.0 g, reacheda peak of 605 g by Day 38, and declinedto 545 g the day before fledging. Body feathersand remigesbegan to show on Days 12 and 15 after which the belly feathersdeveloped a mixtureof white and sooty black.