Breeding ecology of Smith's longspurs (Calcarius pictus) in the Brooks Range, Alaska

Abstract

Alaska's Arctic ecosystem provides critical habitat for nesting songbirds. However, within this region climate change projections indicate a shrubbier future, as well as major shifts in summer weather patterns. The polygynandrous Smith's Longspur (Calcarius pictus) is a little known species that is closely tied to treeless tundra habitat in northern Alaska. I evaluated Smith's Longspur dispersal ability and annual survival rates using seven years of banding data, as well as breeding habitat requirements and reproductive success in two populations in the Brooks Range. Most adults (88%; n = 34) returned to nest in the same breeding neighborhood as previous years, and dispersal distance (x ± SE = 301 ± 70 m) did not differ between sexes. Only 4% of juvenile birds were resighted as adults and dispersal distance (x = 1674 ± 500 m; n = 6) was significantly greater for juveniles than for adults. From 674 capture-recapture histories, I evaluated annual survival and found that adult female survival (50-58%) was only slightly lower than for males (60-63%); juvenile survival was 41%, but was also paired with a low (13%) encounter probability. I examined nest-site selection patterns by comparing habitat measurements from 86 nests to paired random points within the nest area. Nests were typically found in open low shrub tundra and never among tall shrubs (height of tallest shrub x = 26.8 ± 6.7 cm). However, the only predictor of nest location I found was variation in willow height, which was slightly lower at nests than at random points. Daily nest survival rates were estimated from 257 nests and found to be relatively high (0.97-0.99) and consistent across years, and the best approximating model indicated that nest survival was negatively related to the numbers of days below freezing and season date. Despite dispersal ability and resilience to harsh conditions, Smith's Longspurs' response to climate change is unknown. The lack of sex-bias in dispersal and the low sex bias in survival, as well as the weak nest-site selection, may be attributed to the species' social mating system. Unlike most songbirds, multiple inter-mated individuals exist within each breeding neighborhood, altering social dynamics and likely demographic patterns. This is the first study to investigate the breeding biology of Smith's Longspurs at the western extent of their range and provides important conservation information as Arctic regions change.