Demographic consequences of migratory stopover: linking red knot survival to horseshoe crab spawning abundance

Abstract

Understanding how events during one period of the annual cycle carry over to affect survival and other fitness components in other periods is essential to understanding migratory bird demography and conservation needs. Previous research has suggested that western Atlantic red knot (Calidris canutus rufa) populations are greatly affected by horseshoe crab (Limulus polyphemus) egg availability at Delaware Bay stopover sites during their spring northward migration. We present a mass‐based multistate, capture‐recapture/resighting model linking (1) red knot stopover mass gain to horseshoe crab spawning abundance and (2) subsequent apparent annual survival to mass state at the time of departure from the Delaware Bay stopover area. The model and analysis use capture‐recapture/resighting data with over 16,000 individual captures and 13,000 resightings collected in Delaware Bay over a 12 year period from 1997–2008, and the results are used to evaluate the central management hypothesis that red knot populations can be influenced by horseshoe crab harvest regulations as part of a larger adaptive management effort. Model selection statistics showed support for a positive relationship between horseshoe crab spawning abundance during the stopover and the probability of red knots gaining mass (parameter coefficient from the top model b̂ = 1.71, = 0.46). Our analyses also supported the link between red knot mass and apparent annual survival, although average estimates for the two mass classes differed only slightly. The addition of arctic snow depth as a covariate influencing apparent survival improved the fit of the data to the models (parameter coefficient from the top model b̂ = 0.50, = 0.08). Our results indicate that managing horseshoe crab resources in the Delaware Bay has the potential to improve red knot population status.

Conservation status of the American horseshoe crab, (Limulus polyphemus): a regional assessment

“…Other effects of climate change, such as increasing water temperatures and altered storm frequency and severity, could affect the timing and success of spawning activity in some regions. Changes in the timing of spawning activity would have uncertain consequences to horseshoe crab population viability, but could have ecosystem effects by creating mismatches in predator-prey dynamics, particularly those involving migratory shorebirds and horseshoe crab eggs (McGowan et al 2011a;Smith et al 2011). Recent declines in the surf clam population in the midAtlantic region could be due to climate-change induced increases in water temperatures during latesummer and fall (E. Powell, Rutgers University, personal communication); the effects of a declining prey base on horseshoe crab population carrying capacity are unknown.…”

Temporal Migration Shifts in the Aransas-Wood Buffalo Population of Whooping Cranes (Grus americana) Across North America

“…In some instances, birds may adapt to these environmental changes with few noticeable consequences (Both and Visser 2005;Murphy-Klassen et al 2005;Ward et al 2015), while in other cases, the changes may have important consequences. For example, migratory strategies often include arriving at specific locations during specific temporal periods to exploit a specific food resource that historically has predictably been in great abundance for a short time during a certain period of the year (McGowan et al 2011). Changing phenology in either migration or food resource availability can create asynchronies that result in migrating individuals missing the period when key food resources are abundant.…”

Evidence, models, conservation programs and limits to management

“…The steps of developing explicit models of system response to management and then conducting analyses to either discriminate among competing models or estimate key parameters associated with general models have recently led various managers to the recognition that many previously favored management actions are indeed limited in their ability to produce desired outcomes (e.g. Martin et al, 2009bMartin et al, , 2011Alisauskas et al, 2011;Johnson et al, 2011;McGowan et al, 2011). These kinds of results lend greater urgency to the task of implementing conservation programs that use defensible approaches to decision-making.…”