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.