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Colony Attendance and Population Monitoring of Least and Crested Auklets on St

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Colony Attendance and Population Monitoring of Least and Crested Auklets on St The Condor 9297406 0 The CooperOmitholopjd Society1990 COLONY ATTENDANCE AND POPULATION MONITORING OF LEAST AND CRESTED AUKLETS ON ST. LAWRENCE ISLAND, ALASKA ’ JOHN F. PLATT, BAY D. ROBERTS, AND SCOTT A. HATCH Alaska Fish and Wildlif ResearchCenter, U.S. Fish and Wildlife Service, 1011 E. Tudor Rd., Anchorage,AK 99503 Abstract. Diurnal and seasonalpatterns of attendanceof Least Auklets (Aethia pusilla) and CrestedAuklets (A. cristatella)were studiedin 1987 at breedingcolonies on St. Lawrence Island, Alaska. Numbers of aukletsattending eight 200-m2 plots on talus slopeswere counted throughout the day by observers on 11 occasionsthrough the breeding season.Numbers attending smaller plots were recorded on time-lapse film on 7 1 different days. Another 16 200-m2 plots were censusedfor auklets using surfacecounts. Within-day patterns of atten- dance were extremely variable over small and large temporal scales.Peaks of attendance occurredin late morning and late evening, with a 7- to 12-hr period of absencein the middle of the day. Attendance varied markedly between days, and numbers were negatively cor- related with wind speed and the magnitude of tidal oscillations.Patterns of attendancealso varied with stage of breeding, and counts were least variable during incubation and early chick rearing. Whereas Least Auklet numbers peaked during prelaying, Crested Auklet numbers peaked during incubation. Counts indicated that auklets at Kongkok Bay have increasedabout twofold since studies in the mid-1960s. Recommendations are made for future monitoring of auklet populations. Key words: Least Auklet; Aethia pusilla; CrestedAuklet; Aethia cristatella;census; pop- ulation monitoring;St. LawrenceIsland; time-lapsephotography. INTRODUCTION of breeding and nonbreeding auklets to and from Least Auklets (Aethia pus&z) and Crested Auk- breeding sites and related attendance at the sur- lets (A. cristatella) are two of the most abundant face to activities of birds below the surface of seabirds in the North Pacific, but numbers are talus slopes.Despite these advances, no consen- difficult to censusand population estimates for sus has been reached on the best methods for most coloniesare still tentative @owlset al. 1978). monitoring auklet populations. Both species lay their eggs in natural crevices We studied diurnal and seasonal attendance among the rubble of boulder fields or glacially- patterns of Least and Crestedauklets on St. Law- formed talus slopes, and attendance at colonies renceIsland in summer 1987, usingsurface counts is extremely variable. Those factors make it dif- of auklets and time-lapse photography. The pur- ficult to estimate numbers of breeding birds or pose of the study was to identify sourcesof vari- monitor population trends. ation in attendance and refine methods for mon- BPdard (1969b) was the first to develop meth- itoring populations. We compare our data with ods for censusing auklets. He counted birds at- results of previous studies to assesschanges in tending 200-m* plots on talus slopesand extrap- the populations of auklets at St. Lawrence Island. olated to estimate total population sizes of METHODS colonies on St. Lawrence Island, Alaska. How- ever, Btdard did not quantify diurnal or seasonal We worked at Kongkok Bay (63”24’N, 17 l”49’W) variations in attendance. Byrd et al. (1983) and near the southwestcape (Fig. 1); in the area de- Roby and Brink (1986) demonstrated that the scribed in detail by Btdard (1969b). We estab- numbers of Least and Crested auklets in atten- lished 16 200-m* auklet study plots on: (1) the dance on slopes varied widely both daily and inland talus slopesof Owalit Mountain to study seasonally.They also monitored the movements breeding biology (Piatt et al., in press) and at- tendance patterns, and (2) the northern and southern slopesof Kongkok Basin for censusing ’ ’ Received 13 March 1989. Final acceptance2 Oc- (Fig. 1). tober 1989. We counted birds sitting on the surfaceof talus [971 98 J. F. PIATT, B. D. ROBERTS AND S. A. HATCH For comparing our surface counts with those of BCdard and Searing, we averaged the second, T. LAWRENCE third, and fourth highestcounts of auklets at each plot to calculate peak densities. Counts were con- ducted between 05:00-l I:00 Bering Daylight Time (BDT). We found two of the same plots used by Searing, and located other plots in the same vicinity (Lane Iyakitan, pers. observ.). Sur- face countsat Owalit were conductedduring June (prelaying) and at Kongkok in late July (chick rearing). We corrected for seasonalvariation by counting at Owalit and Kongkok simultaneously in July, and extrapolating from the June and July counts at Owalit. We extrapolated from surface oAuklet Plots counts to total populations by using our mea- sures of average auklet densities and Bedard’s estimates of total colony areas for Owalit and 07 1 Kongkok. BERING SEA RESULTS ATTENDANCE PATTERNS Diurnal patterns of auklet attendance were typ- FIGURE 1. Studyarea and locationof auklet plots on St. LawrenceIsland. Contourintervals in feet. ically erratic at small temporal (5 min) and spatial scales(Fig. 2). Least and Crested auklet numbers habitat (hereaftercalled “surface counts”) on eight on time-lapse plots were negatively correlated on of the Owalit study plots every 0.5 hr on 11 73% of 77 count-days observed,and 48% of those different days. We also placed g-mm time-lapse negative correlations were significant. At larger cameras on three Owalit plots with about 1O-m2 (30 min) time scales, Least and Crested auklet areasto take time-lapse photosevery 5 min. Birds numbers were positively and significantly cor- recorded by observers or time-lapse film repre- related each day on all eight Owalit plots (Fig. sent only that portion of the population present 3) and on 94% of time-lapse count-days when on top of the talus rocks (i.e., birds in crevices, the data were averaged over 0.5-hr time inter- flying about the colony, foraging, or loitering at vals. Stronglysignificant correlations (Least: mean sea near the colony are excluded). Auklet num- r = 0.67 f 0.096 SE; Crested: r = 0.62 f 0.23) bers were later counted from the films using a between time-lapse counts averaged over 0.5 hr time-lapse projector. Complete diurnal counts and observer counts on eight Owalit plots were were obtained for 7 1 different days from 30 May observed on all days except 23 August, when few to 26 August. Attendance patterns were analyzed auklets attended the colony (Fig. 3). Time-lapse with nested ANOVA and variance component and surface counts revealed that auklet atten- proceduresin SAS (1985). We used the 5% level dance increasedrapidly and plateaued during the of statistical significance and the term “signifi- morning hours, declined slowly in early after- cant” is usedhereafter in its statistical senseonly. noon until no birds were present for 7-l 2 hr, and BCdard (1969b) censusedauklets prior to egg peaked again at lower levels late in the evening. laying by counting numbers attending a number Analysis of the components of variation in of 200-m2 plots during the early morning, se- numbers of auklets on Owalit plots indicated that lecting the secondto fourth highest counts to get within-day fluctuations accounted for most of a mean density per plot, and extrapolating from the total explained variance in auklet attendance plots to the total area of habitat used by auklets (Least: 78%, Crested: 53%). After removing to get a population estimate. He adjusted surface within-day variation from the analysis, and using counts for the total area of plots covered with only data from 06:00-09:00 BDT (period used suitable substrate,and the depth of the talus rock for censusingby Bedard 1969b), between-day and layer. Searing (1977) used exactly the same pro- between-plot variance accounted for most of the cedure as BCdard (1969b). variation (Table 1). By grouping time-lapse data AUIUET ATTENDANCE PATTERNS 99 DIURNAL ATTENDANCE PATTERNS CRESTED AUKLET 5 8 P bl 0500 0600 0700 0600 0900 1000 1100 1200 2400 0100 0200 TIME OF DAY (21 JUNE) PIGURE 2. Diurnal attendanceof Leastand Crestedauklets at plot 3, Owalit Mountain on 21 June 1987. Countsare for a 10-m>area every 5 min from time-lapsefilm. Note breakin time between12:10-23:55, when no aukletswere present. into hours and months, we obtained an inte- dance of both specieswas negatively correlated gratedpicture ofauklet attendance (Fig. 4) which with wind speed, which accounts for many days was more accuratethan the observer counts (Fig. of low attendance, particularly in June (Figs. 3 3) becausebetween-day variance was smoothed and 5). Attendance also was negatively correlated out by the large sample size. In most respects, with the range of daily tidal oscillations. Corre- patternsrevealed by time-lapse and surfacecounts lations improved when data were grouped over were similar. Attendance shifted from early 7-day intervals. Crested Auklet attendance was morning to afternoon hours as the breeding sea- also positively correlated with daily maximum son progressed,and Crested Auklet attendance air temperature and rainfall, although those cor- peaked in July whereas Least Auklet attendance relations were probably an artifact of analysis was similar in June and July. due to a seasonal trend of increasing air tem- Integration oftime-lapse data within days (Fig. perature and rainfall. 5) revealed that Least Auklet attendance peaked POPULATION TRENDS during prelaying whereas Crested Auklet atten- dance slowly built up to a peak during incuba- At Kongkok Basin, we observed higher densities tion. Both speciesstopped attending the surface of Least Auklets, but similar densities of Crested of talus slopesafter mid-August, although chicks did not fledge until late August and early Sep- TABLE 1. Componentsof variationin attendanceof tember (Piatt et al., in press). Figure 5 also il- Leastand Crestedauklets at plotson Owalit Mountain, lustratesthe magnitude of daily variation in sur- St. LawrenceIsland.
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