Demographic features of a lapland longspur population near Barrow Alaska

-Breeding density, clutch size, hatching and fledging success, and survival of adult Lapland Longspurs (Calcarius lapponicus) were monitored over a 7-year period near the Naval Arctic Research Laboratory, Barrow, Alaska. Nesting begins as soon as the tundra starts to clear of snow and appears to be timed so that the young of the year reach independence before the end of adult insect emergence. Arthropod prey become abruptly scarce after the period of insect emergence and thus probability of success for late broods is low. Time of nesting is also discussed in relation to factors of predation and timing of molt. At least 42.9% of males and 45.4% of females survived the next season after 1 year of age. Maximum longevity observed for both sexes is 6 years. Mean clutch size for all years investigated was 5.06 eggs per clutch. Clutch size showed both yearly and seasonal variation. The data indicate that timing of nesting is the chief factor in the observed clutch size differences, further modified by habitat quality, second nesting attempts, and probably age of female. Over a 4-year period the longspur breeding population on a 17-ha study plot declined from 15 to 2 breeding females. Life-table analysis indicates that low fledgling success for 3 consecutive years apparently was the main cause of this decline. Overall mean egg success was 44.0%, but close to 60% in 4 years considered more "normal. " The low egg success was due to 3 consecutive years of high predation, which may have been related to the disrupted lemming cycle of the Barrow region. -Museum of Vertebrate Zoology, University of California, Berkeley, California 94720. Present address of senior author: Patuxent Wildlife Research Center, Laurel, Maryland 20811. Accepted 9 December 1975. THE increase in fieldwork in the Arctic in the 1950's and 1960's has made it possible to examine various aspects of the demography of passerine birds there (Ricklefs 1969, 1973; Hussell 1972). Even so, information on density, clutch size, and hatching success of arctic birds is generally scarce, and only a few recent studies (e.g.Williamson 1968, Williamson and Emison 1971, Hussell 1972) had been carried out for more than one season. The demographic data presented here represent part of an investigation dealing with the role of the Lapland Longspur (Calcarius lapponicus) in the arctic coastal tundra ecosystem of northern Alaska. Data on clutch size, hatching and fledging success, and survival of adults, which span a seven-year period (1967-1973), are analyzed by life-table techniques. During the course of the study longspur breeding density decreased drastically at Barrow. The life-table analysis helps explain the observed decline. Some data pertinent to various aspects of this paper are also drawn from work on the Lapland Longspur by F. A. Pitelka during the period 1951-1969. Other parts of this study, dealing with diet, activity patterns, molt, and bioenergetics will be published elsewhere. Background information on coastal tundra as a habitat is available in Britton (1957) and Wiggins and Thomas (1962). The total ecological setting is compactly summarized by Bunnell et al. (1975).