Rapid population decline in red knots: fitness consequences of decreased refuelling rates and late arrival in Delaware Bay

Abstract

Most populations of migrant shorebirds around the world are in serious decline, suggesting that vital condition-dependent rates such as fecundity and annual survival are being affected globally. A striking example is the red knot (Calidris canutus rufa) population wintering in Tierra del Fuego, which undertakes marathon 30,000 km hemispheric migrations annually. In spring, migrant birds forage voraciously on horseshoe crab eggs in Delaware Bay in the eastern USA before departing to breed in Arctic polar deserts. From 1997 to 2002 an increasing proportion of knots failed to reach threshold departure masses of 180-200 g, possibly because of later arrival in the Bay and food shortage from concurrent over-harvesting of crabs. Reduced nutrient storage, especially in late-arriving birds, possibly combined with reduced sizes of intestine and liver during refuelling, had severe fitness consequences for adult survival and recruitment of young in 2000-2002. From 1997 to 2002 known survivors in Delaware Bay were heavier at initial capture than birds never seen again, annual survival of adults decreased by 37% between May 2000 and May 2001, and the number of second-year birds in wintering flocks declined by 47%. Population size in Tierra del Fuego declined alarmingly from 51,000 to 27,000 in 2000-2002, seriously threatening the viability of this subspecies. Demographic modelling predicts imminent endangerment and an increased risk of extinction of the subspecies without urgent risk-averse management.

Avian Influenza Virus Infection Dynamics in Shorebird Hosts

“…Although AIV has not been detected on wintering grounds, available information is limited. More information regarding when and where Red Knots are exposed or infected would be helpful to understand what role, if any, LPAI infection has had on recent population declines (Baker et al, 2004;Niles et al, 2009).…”

Prioritizing tropical habitats for long-distance migratory songbirds: an assessment of habitat quality at a stopover site in Colombia

“…During migration birds experience high mortality (Sillett andHolmes 2002, Newton 2006), and events on migration can also affect demography through carry-over effects on reproductive output (Baker et al 2004, Finch et al 2014. The success of migration typically depends on a series of stopover sites distributed between the breeding and stationary nonbreeding grounds, where the energy reserves for long-distance flights are acquired (Weber et al 1998).…”

“…The success of migration typically depends on a series of stopover sites distributed between the breeding and stationary nonbreeding grounds, where the energy reserves for long-distance flights are acquired (Weber et al 1998). Birds are therefore vulnerable to changes that alter the resource base at stopovers (Baker et al 2004), especially if populations rely on a small number of sites to acquire energy, as recent stopover studies and new tracking technologies suggest (Bayly et al 2013, McKinnon et al 2013a). Identifying and prioritizing stopover regions and habitats is therefore a research and conservation priority (Faaborg et al 2010).…”

Body condition of shorebirds upon arrival at their Siberian breeding grounds

“…Instead of being channelled into eggs, nutrient stores carried to the breeding grounds may also be metabolised during the period directly after arrival, when food availability is limited and unpredictable owing to weather and snow conditions (Morrison 1975;Sandberg 1996;Baker et al 2004;Morrison et al 2005). Such stores may be important for survival and reproduction: unusually cold early summers in 1972 and 1974 caused extensive mortality of adult Red Knots Calidris canutus in northern Greenland and Canada (Morrison 1975;Boyd and Piersma 2001), and birds departing from Iceland with below-average mass suffered more than heavier birds (Morrison 2006;Morrison et al 2007).…”