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Population Declines of King and Common Eiders of the Beaufort Sea’

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Population Declines of King and Common Eiders of the Beaufort Sea’ SHORT COMMUNICATIONS 219 at CEBC. Bob Dawson at the Department of Zoology GR~NDLUND, S., AND H. MIKKOLA.1969. On the ecol- of the University of Oxford sexed the blood samples ogy of the Short-eared Owl in Lapua Alajoki in by genetic analyses. Peter Colston (NHM, Tring) al- 1969. SuomenselanLinnut 4:68-76. lowed accessto the NHM collection. To all of them, HOLT, D. W., AND S. M. LEASURE.1993. Short-eared we expressour gratitude.This work was part of a pro- Owl. In A. Poole and E Gill [EDS.], The birds of gram financed by a grant from the Rtgion Poitou Cha- North America, No. 62. The Academy of Natural rente and CNRS to I? Duncan and V. Bretagnolle. Sciences, Philadelphia, and American Omitholo- gists’ Union, Washington,DC. HOLT,D. W., M. MELVIN, AND B. STEELE.1992. Nest- LITERATURE CITED ling growth rates of Short-eared Owls. Wilson Bull. 104:326-333. CRAMP,S. [ED.]. 1983. The birds of the Western Pa- MIKKOLA,H. 1983. Owls of Europe. T & A D Poyser, learctic. Vol. 3. Oxford Univ. Press, Oxford. Calton, UK. DE CORNULIER,T., R. BERNARD,B. ARROYO,AND V. RICKLEFS,R. 1983. Avian post-natal development, p. BRETAGNOLLE.1998. Hibou des maraisAsio Jam- l-83. In D. S. Famer and J. R. King [EDS.], Avian meus: nidification exceptionnelleen plaine ctrkal- biology. Vol. 7. Academic Press, New York. i&e. Alauda 66:229-234. ZACH, R., Y. LINER, G. L. RIGBY, AND K. R. MAYOH. GRIFFITHS,R., C. Y. MIKE, K. ORR, AND R. J. G. DAW- 1984. Growth curve analysis of birds: the Rich- SON. 1998. A DNA test to sex most birds. Mol. ards model and proceduralproblems. Can. J. Zool. Ecol. 7:1071-1075. 62:2429-2435. The Condor 102:219-222 0 The CooperOmithologxal Society 2000 POPULATION DECLINES OF KING AND COMMON EIDERS OF THE BEAUFORT SEA’ ROBERTS. SUKDAM North Slope Borough Department of Wildlife Management, Box 69, Barrow, AK 99723, e-mail: [email protected] D. LYNNE DICKSON Canadian Wildlife Service, Environment Canada, Room 200, 4999-98 Ave., Edmonton, AB T6B 2X3, Canada JANEY B. FADELY~ U.S. Fish and Wildlife Service, Ecological Services, 605 West 4th Ave., Room G-62, Anchorage, AK 99501 LORI T. QUAKENBUSH~ U.S. Fish and Wildlife Service, Northern Alaska Ecological Services, 101 12th Ave. Box 19, Fairbanks, AK 99701 Abstract. King (Somateria spectabilis) and Com- dardized procedure, the King Eider population ap- mon Eiders (S. mollissima v-nigra) wintering off west- peared to remain stable between 1953 and 1976 but em North America migrate past Point Barrow, Alaska declined by 56% (or 3.9% year-‘) from approximately and acrossthe Beaufort Sea to nest in northern Alaska 802,556 birds in 1976 to about 350,835 in 1996. The and northwesternCanada. Migration countswere con- Common Eider population declined by 53% (or 3.6% ducted by various researchersat Point Barrow during year-‘) from approximately 156,081 birds in 1976 to 1953, 1970, 1976, 1987, 1994, and 1996. We exam- about 72,606 in 1996. Reasons for the declines are ined population trends by standardizingthe analysisof unknown. the migration counts in all years. Based on this stan- Key words: Beaufort Sea, Common Eider, King Eider, mortality, population trend, Somateria mollis- sima v-nigra, Somateria spectabilis. ’ Received 23 March 1999. Accepted 18 August 1999. 2Present address: U.S. Fish and Wildlife Service, King (Somateria spectabilis) and Common Eiders (S. Migratory Bird Management, 3000 Vintage Blvd., mollissima v-nigra) wintering in the Bering Sea and Suite 240, Juneau,AK 99801. north Pacific Ocean migrate north to nesting areas in 3Present address: University of Alaska Fairbanks, Russia, Alaska, and northwesternCanada. Most of the School of Fisheries and Ocean Sciences, Fairbanks, eiders that nest in Alaska and Canada migrate past AK 99775. Point Barrow, Alaska and across the Beaufort Sea. 220 SHORT COMMUNICATIONS During the molt and fall migrations, eiders again pass TABLE 1. Estimated passage and 95% confidence close to Point Barrow as they head west and south to intervals (CI) for the number of King and Common the Chukchi and Bering Seas. An account of the spec- Eiders migrating past Point Barrow during a standard- tacular migrations of eiders past Point Barrow was first ized period in the spring (1 May to 4 June) and fall published more than 100 years ago (Murdoch 1885), (13 July to 7 September). although systematic efforts to estimate the magnitude of the passage did not occur until much later (Thomp- King Eider Common Eider son and Person 1963, Woodby and Divoky 1982, Suy- Season! dam et al. 1997). year Passagea CIb Passagea CIb King and Common Eider populations are not rou- 1953’ 759,999d NA” tinely monitored; there are few data on the sizes or 1970’ 760,199 NA trends of the populations. Two studies in the early 1976’ 802,556 NA 156,081 NA 1990s suggested that the King Eider population of the 1987’ 555,870 103,229 95,069 28,261 Beaufort Sea had declined markedly over the previous 1994’ 345,489 147,877 74,65 1 22,317 20 years (Dickson et al. 1997, Suydam et al. 1997). 1994’ 288,362 46,229 The objective of this paper is to examine the available 1996’ 371,452 107,697 72,606 13,606 data on population trends of the King and Common 1996’ 330,218 70,725 Eiders of the Beaufort Sea. a Projected passage of eiders for 1953 (Thompson and Person 1963). 1970 METHODS (Johnson 1971), 1976 (Woodby and Divoky 1982). 1987 and 1994 (Suydam et al. 19971, and 1996 (Suydam and Quakenbush, unpubl. data). We compared estimates of the number of King and b Confidence intervals were calculated using a stratified sampling proce- Common Eiders migrating past Point Barrow in 1953 dure (Thompson 1992) with days bang used as the strata. c Fall migration. (Thompson and Person 1963), 1970 (Johnson 1971), * Estimated passage was not divided between King and Common Eiders 1976 (Woodby and Divoky 1982), 1987, 1994 (Suy- by Thompson and Person (1963), thus we used the percentage of King and Common Eiders observed in the migration during 1970 by Johnson (197 I). dam et al. 1997) and 1996 (Suydam and Quakenbush, e NA = Not available. unpubl. data). The duration of the migration counts f Spring migration. varied among the studies, thus we standardized our analysis procedures to include data collected only be- tween 1 May to 4 June for spring migration and 13 Eider population had declined (1976 to 1996, F,,, = July and 7 September for summer/fall migration. The 74.9, P = 0.01) by 56% (or 3.9% year’) to approxi- standardized periods contained mostly adult eiders. mately 350,835. The number of Common Eiders pass- Few immature King Eiders migrate past Point Barrow ing Point Barrow during the spring declined by 53% (Suydam and Quakenbush, unpubl. data). During the (or 3.6% year-r) from 156,081 in 1976 to 72,606 in fall, the young-of-the-year do not first appear at Point 1996 VI.2 = 58.0, P < 0.02). Barrow until the very end of August or the first week DISCUSSION of September (Johnson 1971, Timson 1976), thus few young are included in the standardized summer/fall Standardized analysis of results from migration counts time period. of eiders at Point Barrow provide evidence that the We conducted simple linear regression analysis on number of King and Common Eiders of the Beaufort point estimates of eider numbers (Norusis 1993). Be- Sea may have declined markedly from 1976 to 1996. cause the King Eider population appeared stable at A change in the number of migrating eiders, however, least through 1976, we conducted regression analysis could reflect a change or shift in the migration route. only on 1976 to 1996 estimates, both spring and sum- There are no scientific data available to evaluate mer/fall counts. Because estimates were obtained for changes in migration routes, although Eskimo hunters both spring and summer/fall migrations in 1994 and indicate that there has been no change (C. D. N. Brow- 1996, point estimates for each of these years are an er, pers. comm.). average of the two counts. For Common Eiders, we The data indicating a decline in eider populations only used the spring migration data for trend analysis. are compelling but need to be viewed with some cau- Whereas fall migration of most adult King Eiders past tion. Suydam et al. (1997) pointed out some of the Point Barrow occurs in July and August, many adult difficulties associated with comparing eider migration Common Eiders remain east of Point Barrow until late counts, including: (1) differences in watch effort and September or October (Barry 1986, Suydam et al. duration of the counts, (2) fall counts miss some fe- 1997). Counts during 1953 and 1970 ended in early males that migrate late in the season and may contain September well before the conclusion of the migration some young-of-the-year birds, (3) lack of variance es- of adult Common Eiders (Thompson and Person 1963, timates for early counts, (4) interannual variation in Johnson 1971). Therefore, the fall counts could not be timing of the migration, and (5) potential differences compared with the spring counts that appear to contain in counting techniques or abilities among observers. most of the Beaufort Sea breeding eiders. We have tried to minimize the effects of the first two factors by standardizing the counts across years. Too RESULTS few data exist to sufficiently evaluate the latter three The estimated numbers of King and Common Eiders factors. By standardizing the results among all years, passing by Point Barrow during the standardized pe- we minimized, but did not eliminate, potential effects riods are presented in Table 1.
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