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Black-Legged Kittiwakes, Common Murres, and Pelagic Cormorants

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Black-Legged Kittiwakes, Common Murres, and Pelagic Cormorants - ~ . '· - U B.R. '· · USFW~ Anchorage Population and Productivity Surveys of Black-Legged Kittiwakes, Common Murres, and Pelagic Cormorants at Cape Peirce, Alaska, Summer 1987 by Lisa Haggblom and Allyn O'Neil Togiak NWR ·Volunteers Key Words: black-legged kittiwake, common murre, pelagic cormorant, Cape Peirce, seabird population, seabird productivity U.S. Fish and Wildlife Service Togiak National Wildlife Refuge P.O. Box 270 Dillingham, Alaska 99576 I' . Novembe r 30, 1987 ' j ... \ . .,-· ., ( .. 1 INTRODUCTION There is a growing ·concern over the recent decline of many seabird species in the Bering Sea. Cape Peirce, within Togiak National Wildlife Refuge, reportedly has the largest seabird colony along the mainland coast of Alaska <Lloyd, 1985). The refuge has enlisted the help.of volunteers to monitor seabird populations and productivity at Cape Peirce sine~ 1984, althoucih seabird studies have been conducted intermittently since 1976 •. · A cabin to house researchers is within walking distance of the major bird colonies at Cape Peirce, making the area convenient for thes~ studies <Figure• ~and 2>. The primary species, to which this study is devoted, are black-legged kittiwakes CRissa tridactyla>, common murres CUria aalge>, and pelagic cormorants <Phalacrocora>:,,pelagicus). Horned and tufted puffins <Fratercul a cor·ni CLtl ata and · rhata> , pigeon guillemots (Cepphus calumba), and glaL us-winge gulls CLarus glaucescens) also nest at the Cape an~'f¥ ai·ak Island, but in lower numbers. / USFWS 11\pchorage MATERIALS .AND METHODS Population Counts The 1987 seabird study . began May 25, shortly after volunteers arrived at Cape Peirce, and ended September 9. Black­ legged kittiwakes, common murres, and pelagic cormorants were studied because they were most visible on the cliff ledges and the most ~bundant species. Black and white, 8 x 10 photographs taken i~ 1976 and 1984 outlined each study plot. Using· binoculars and/or a spotting scope, volunteers counted only those birds within the boundary lines as deline<;ited in the photographs. Aluminum stakes, set up by previous researchers in 1984, mark observation points , and insure consistent study plot identification between years. To make counting easier and hence ~ore accurate, individual ahd groups of birds were counted separately. For e>:~mple, a group of bir·ds was any number of birds isolated from others of its species by two or more body lengths, or by a bird of another species. Major study plots were census~d three to four times a week, and censusi ng was conducted at aP.pro:·: i matel y the same time of day to reduce diurnal variance. Population counts for 1987 are compared with data from previous years. As Higgins and Herter (1985) recommended, population counts from each study plot were averaged from May 25 to September 9, the~ the study plot averages totaled. The total area of all the study plots was determined to be approximately one-half the total occupied mainland ar~a, so the census averages Were multiplied by two to give the total mainland populations <Higgins, 1985). This method provides a means for future comparisons and indicates general population trends. I .. t •' rJ ,' 2 Plot 27 was destroyed due to wave action and erosion between October 1986 and May 1987. Plot 41 was eliminated irom censusing due to observer disturbance to the seabirds. Shaiak Island is a small, rocky island adjacent to plots 1-18 on the southeast coast of the Cape Peirce peninsula, and attracts most of the seabird population that would otherwise nest on the mainland. Therefore, these plots were observed infrequently due to to 'their consistently low population numbers. Due to time limitations, Plot 29 was also observed infrequently. Censuses of the above­ mentioned plots could be conducted ever'y 2-3 years. Plot 20.4 was subdivided into three subplots to facilitate more accurate counting--20.41, 20.42, and 20.43. Productivity BLACK-LEGGED KITTIWAKES AND PELAGIC CORMORANTS Only study plots where the birds could be viewed easily with the naked eye or binoculars were included in the producti~ity surveys. The same photographs used for population counts were covered with plastic overlays. Each nest site ·Was then circled and numbered on the photos and observed every one to five days throughout the breeding season. Approximate dates of egg~laying, hatching, predation, and fledging were recorded. The number of successful kittiwake and cormorant nest attempts was calculated as the number of nests containing eggs per totai number of nests. Mean clutch size was cal~ulated only for those kittiwake and cormbrant nests with eggs. Hatching success was calculated as the number of chicks hatched per number of eggs laid. In addition, number of eggs hatched per total. number of nests was also .noted for kittiwakes <Petersen and Sigman, 1976> • Observers oiten could not tell if an egg had been predated, or if an egg had hatched and been predated between visits to the study plots. For this reason, only those eggs known to have hatched were used in the calculations. Thus, the hatching success results are minimum values. Reproductive success was determined for kittiwakes and cormorants by the number of chicks fledged per number of nests with eggs. Productivity of kittiwakes and cormorants was calculated as the number of chicks fledged per number of nesting attempts. COMMON MURRES Murres do not build nests, but lay their eggs directly on cliff ledges. The eggs and chicks are obscured from view by the adults. Consequently, murre chicks were not identified until they were ready to leave the cliff ledges, or until they were 1.' seen swimming in the water with the adults prior to flying tiffshore. The above parameters des~ribed for kittiwakes and cormorants were not applicable to murres as such, but the number of fledgl~ngs was compared with the total population of murres. "' ., ' . l. 3 RESULTS AND DISCUSSION Black-legged Kittiwakes The population of black-legged kittiwakes at Cape Peirce in 1987 <4,020) is approximately 1.7 times that of 1986 <2,440), and comparable to that of 1985 <3,800) <Table 1). The majority of the regularly observed plots show an increase in numbers of kittiwakes from 1986 to 1987, as shown in Tables 2 and 3. Birds were present at the study plots when volunteers arrived on May 21. They began gathering nest-building material from the area ponds May 30, and continued this activity until June 15. The birds flew single-file in specific flight paths to and from the ponds, gathering and washing their nesting material. The number of nesting attempts at the major productivity study plots- in 1987 was consistent with numbers recorded in 1984 and 1985, but slightly lower than those of 1986 (Table 4>. Many nests are destroyed by predation, thus the number of nests will decline as the breeding season progresses. The first kittiwake egg. was observed on June 24, and egg­ laying was complete by approximately. July 20. Of the 128 nests observed, at least 42% contained eggs. The remaining nests either had no eggs, or the adults incubated so tightly that nest contents were never seen. The percentage of . nests with eggs in 1987 is comparable to those of previous years <Table 5>. Of the 54 nests that were known to contain eggs, 42 had one egg, and 12 had two eggs, giving an average of 1.22 eggs per nest. No nest was ever seen containing more than two eggs or more than one chick. The clutch size decreased slightly, but not significantly, from 1.40 in 1986 <Table 5). Hatching began approximately July 9 and was completed by August 3. 49% of the eggs hatched. This minimum hatching success value falls ·within the range recorded for 1986 (32-64%) <Table 5). Of the 32 chicks observed, 8 were believed to have fledged (25%) •. The remaining chicks were either· pr·eyed upon, or· died due to starvation, exposure, etc... The eggs and chicks were normally attended by at least one adult. When adults occasionally left the nests unguarded, they may have resorted to foraging further away from the nest sites or for longer periods of time if they were unable to locate sufficient food supplies nearby. Ravens and glaucous-winged gulls were the major predators of kittiwake eggs and chicks. The presence of volunteers at the study plots may also have scared the adults from the nests, contributing to egg and chick mortality. However, steps were taken to minimize this factor, and no obvious disturbance was noticed. Reproductive success, or number of chicks fledged per nest with eggs, was 15%. This is greater than that of 1984-1986, when reproductive success was 1% or less. Productivity, or number of chicks fledged per nest attempt, was 6%. Kittiwake productivity ,. ·' .... 4 is typically low, but was greater in 1987 than 1984-1986 C0-1%). Common Mur·r·es The population of common murres for 1987 <5,735) was comparable to that of 1986 <5,000), yet half the estimated population for 1985 (10,300) <Table 1). The individual plot averages were comparable to those of 1986 <Tables 2 and 3). Egg laying began June 9, and continued throughout mid­ August. A total of five eggs was observed on 3 study plots. After the initial identification the eggs were either hidden from view by the adults or preyed upon. A total of four chicks was observed on 3 study plots, although no eggs were observed for these chicks. Five chicks were seen on August 7, swimming in the surf zone with their parents and other adult murres~ Their distinct calls to their par·ents aided r·esearchers in 1 ocati.ng them in the water. The last chicks to be observed were on study plot 31, on August 17.
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