Foraging ecology mediates response to ecological mismatch during migratory stopover

Abstract

Impacts of ecological mismatches should be most pronounced at points of the annual cycle when populations depend on a predictable, abundant, and aggregated food resource that changes in timing or distribution. The degree to which species specialize on a key prey item, therefore, should determine their sensitivity to mismatches. We evaluated the hypothesis that the effects of ecological mismatch during migratory stopover are mediated by a species’ foraging ecology by comparing two similar long‐distance migratory species that differ in their foraging strategies during stopover. We predicted that a specialist foraging strategy would make species more sensitive to effects of mismatch with a historically abundant prey, while an active, generalist foraging strategy should help buffer against changing local conditions. We estimated arrival times, start of mass gain, and rate of mass gain during spring stopover in Delaware Bay, USA. At this site, shorebirds feed on a temporally aggregated food resource (horseshoe crab Limulus polyphemus eggs), the timing of which is linked to water temperature; red knot (Calidris canutus rufa) specializes on these while the ruddy turnstone (Arenaria interpres) feeds more generally. We used a hierarchical nonlinear model to estimate the effect of mismatch between shorebird arrivals and timing of crab spawning on the timing and rate of mass gain over 22 yr. In years with cooler water temperature, crabs spawned later, which was associated with later and faster mass gain for the knots. Turnstones exhibited less inter‐annual variation in the timing and rate of mass gain than knots, and we found no relationship between mass gain dynamics and the availability of horseshoe crab eggs for this generalist species. Long‐distance migrants rely on predictable resources en route and even when these linkages are simple and predictable, populations can be vulnerable to change; these results suggest that generalist foraging strategies may buffer migratory species against phenological mismatch. We provide a framework to evaluate population responses to changes in prey phenology at sites vulnerable to climatic change.

Migratory vertebrates shift migration timing and distributions in a warming Arctic

“…During spring migration, at least some species of waterfowl appear to track peaks in food quality and availability [49][50][51] and the onset of ice break-up and snowmelt at staging sites [52,53]. This, however, does not appear to be the case for all species of waterfowl [51] nor for shorebirds [54]. Birds of prey also track snowmelt during northward migration, possibly as areas with melting snow contain high availability of rodent prey [38].…”

Intra- and inter-population variation in sensitivity of migratory sockeye salmon smolts to phenological mismatch

“…life span, age at maturity, migration timing), physiology (e.g. disease resistance, metabolic scope), and plasticity could further predict individual-or population-level sensitivity to phenological mismatch (Ohlberger et al 2014, Knell & Thackeray 2016, Tucker et al 2019. For example, populations with complex age structure may be better able to buffer total or partial loss of a cohort due to mismatch (Ohlberger et al 2014).…”

“…For example, species that have a single seasonal life history event (i.e. univoltine organisms that reproduce once annually; Knell & Thackeray 2016), have a simplified population structure (age or size at age; Ohlberger et al 2014), rely heavily on a single prey type (specialist predators; Tucker et al 2019), or are less plastic (regarding both phenology and prey type) are more likely to be sensitive to phenological mismatches (Cushing 1990, Durant et al 2007, Miller-Rushing et al 2010). However, the population and individual traits that may influence sensitivity to phenological mismatch have received much less attention.…”

Assessing conservation conflict: Does intertidal oyster aquaculture inhibit foraging behavior of migratory shorebirds?

“…A significant factor contributing to red knot population recovery is horseshoe crab egg abundance in the Delaware Bay (Baker et al 2004, McGowan et al 2011, Loveland and Botton 2015). While red knots have received the most conservation attention, several additional sandpipers rely heavily on horseshoe crab eggs during their stopover in Delaware Bay (Gillings et al 2007, Mizrahi and Peters 2009, but see Tucker et al 2019) and have also experienced notable declines that have been associated with the reduction of horseshoe crab eggs (Haramis et al 2007).…”