The Red Knot (Calidris canutus rufa) decline in the western hemisphere: is there a lemming connection?

Abstract

Numbers of Western Atlantic Red Knots (Calidris canutus rufa (A. Wilson, 1813)) have declined since 1980, with a sustained downward trend observed after 1998. Because the reproductive output of a closely related Eurasian subspecies (Calidris canutus islandica (L., 1767)) is known to be low when lemming numbers are low, and because lemming cycles in Fennoscandia were recently interrupted, we investigated the relationship between the rodent cycle in arctic Canada and numbers of C. c. rufa migrating through the United States. Shooting records from Cape Cod in the 1800s and Red Knot counts on the Delaware Bay from 1986 to 1998 cycled with 4-year periods. Annual peaks in numbers of Red Knots stopping in the Delaware Bay in 1986–1998 occurred 2 years after arctic rodent peaks more often than expected at random. The results suggest that the reproductive output of C. c. rufa was linked to the rodent cycle before the Red Knot decline. There is no evidence that such a link existed after 1998. These findings are consistent with the hypothesis that an interruption of the rodent cycle in Red Knot habitat could have been a driver in the recent Red Knot decline. Field studies in the Arctic are needed to further investigate this hypothesis.

Impacts of nest predators and weather on reproductive success and population limitation in a long‐distance migratory songbird

“…Our results support the hypothesis that reproductive success aff ects redstart population size. Annual nest success in our study population explained over 34% of the variance often cited as a species that is limited by events during the migration period, may in fact be limited by nest predators on the breeding grounds as well (Fraser et al 2013).…”

“…Breeding season limitation also occurs in spruce woods warbler species responding numerically following outbreaks of spruce budworm caterpillars Choristoneura fumiferana across the North American boreal forest (Crawford and Jennings , Venier and Holmes ), in cavity nesting birds in western North America responding similarly to outbreaks of spruce budworm and mountain pine beetle (Norris et al ), and in the endangered Kirtland's warbler Setophaga kirtlandii rebounding from near extinction following fires that created optimal breeding habitat combined with a reduction in the abundance of brown‐headed cowbirds that cause nest failure (reviewed by Bocetti et al ). Even red knots Calidris canutus , often cited as a species that is limited by events during the migration period, may in fact be limited by nest predators on the breeding grounds as well (Fraser et al ).…”

Full Issue

“…Knowing that lemming abundance may be a potential cue for some species would seem to assist in selecting sites, but, unfortunately, this factor is regulated by weather patterns (Hodkinson et al 1996, Krebs et al 2002) that could change drastically under predicted future climate change; for example, fewer regular rodent peaks (Kausrud et al 2008) are predicted under projected climate change. Viewed at an individual bird level, the absence, moderation, or decoupling of such cues may decrease the ability of individuals to determine the best locations to settle and, consequently, decrease their nest survival and ultimately the overall population size (Fraser et al 2013).…”

Foraging ecology mediates response to ecological mismatch during migratory stopover

“…, Fraser et al. , McGowan , van Gils et al. ), conservation management actions in the Delaware Bay region have focused on restoring shorebird stopover habitat and maintaining horseshoe crab populations.…”

“…Declining horseshoe crab abundance due to past unregulated harvest has been suggested as the cause of observed declines in the numbers of birds seen in Delaware Bay during stopover (Baker et al 2004, Niles et al 2008, especially the red knot (Calidris canutus rufa), which is listed as Threatened under the United States Endangered Species Act (79 FR 73705 73748). Although more recent studies indicate that deteriorating Arctic conditions may be an important driver of population declines (McGowan et al 2011, Fraser et al 2012, van Gils et al 2016, conservation management actions in the Delaware Bay region have focused on restoring shorebird stopover habitat and maintaining horseshoe crab populations. As horseshoe crab and red knot populations recover with the aid of strict horseshoe crab harvest regulations , the ability of birds to reach adequate departure mass may be important for population stability (Baker et al 2004).…”