The effect of benthic prey abundance and size on red knot (Calidris canutus) distribution at an alternative migratory stopover site on the US Atlantic Coast

Cohen, Jonathan B.; Karpanty, Sarah M.; Fraser, James D.; Truitt, Barry R.

doi:10.1007/s10336-009-0462-7

Cited by 15 publications

(21 citation statements)

References 33 publications

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“…It has been hypothesized that the decline in TDF knots may also have been driven by the lack of sufficient horseshoe crab eggs in Delaware Bay (Baker et al 2004). Our study and other recent work explores this hypothesis linking red knot and crab declines as well as other possible hypotheses such as limiting factors at other northerly stopover sites (Cohen et al 2009, 2010 b ). Much work remains to be done to explore possible limiting factors on the knots' Arctic breeding grounds (Niles et al 2008).…”

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confidence: 59%

Sufficiency of horseshoe crab eggs for red knots during spring migration stopover in Delaware Bay USA

et al. 2011

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Horseshoe crab (Limulus polyphemus) eggs are a dietary staple of the red knot (Calidris canutus) during its spring stopover on the Delaware Bay. Numbers of knots stopping in Delaware Bay declined in the 1990s concurrent with a decline in horseshoe crabs, leading to the hypothesis that reduced horseshoe crab egg abundance limited the red knot population. Management efforts, including a seasonal harvest moratorium in the Delaware Bay, have been instituted to restore crab populations to levels of sustainable use by multiple users, including migratory birds. Our objective was to evaluate the sufficiency of horseshoe crab eggs in Delaware Bay in May–June 2004 and 2005 for knots to refuel for their migratory flight to the Arctic breeding grounds. We examined egg counts to determine if there were fewer high egg‐density sites later than earlier in the day and season, as migrating birds might deplete this resource. We studied foraging rates at red knot locations to determine if foraging probes increased with time of day and season as birds depleted surface eggs by pecking, then began probing for subsurface eggs. Finally, we experimentally tested whether red knots and their competitors depleted horseshoe crab eggs. Crab egg numbers at knot foraging sites did not decline throughout the day or season in 2004. In both years, we found no evidence that knots switched from pecking to probing with increases in time since sunrise or start of the stopover. Egg numbers were similar in exclosed and accessible plots on crab nesting depressions and in areas of open intertidal zone, but were significantly lower in accessible than in exclosed plots in the wrack line. Our results indicate that horseshoe crab eggs in Delaware Bay were sufficient to support the refueling of the present‐day stopover population of red knots. If an increase in the availability of crab eggs to foraging birds does not result in an increase in knot numbers, managers must prioritize mitigation of limiting factors at other historically important spring stopovers and on the poorly understood breeding and wintering grounds in addition to the Delaware Bay. © 2011 The Wildlife Society.

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confidence: 59%

Sufficiency of horseshoe crab eggs for red knots during spring migration stopover in Delaware Bay USA

et al. 2011

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“…The most common substrate within the active beach zone is sand. Sand beaches support populations of coquina clams (Donax variabilis) that are known to be used by red knots during spring migration both within this study area (Cohen et al 2010) and elsewhere (González et al 1996). Intertidal peat banks are much less common within this system than open sand beach and are distributed in patches along the island chain.…”

Section: Study Areamentioning

confidence: 75%

“…The survey results presented here provide support for a slight decline in bird numbers between the 1990s and the 2000s (24%) compared to a decline of 60-80% in Delaware Bay between 1986 and 1992 (Clark et al 1993, Niles et al 2008; this may indicate that the relative importance of the barrier islands within the broader mid-Atlantic staging complex has increased over the past 2 decades. Recent suggestions of an absolute increase in the number of red knots using the islands (Cohen et al 2009(Cohen et al , 2010 were not supported.…”

Section: Discussionmentioning

confidence: 88%

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Spring migration of red knots along the Virginia barrier islands

Watts

Truitt

2015

J Wildl Manag

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We conducted low-altitude, aerial surveys from the last week of April through the first week of June (1995, 1996,(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013) to assess patterns in bird abundance, migration phenology, and habitat use of red knots (Calidris canutus rufa) staging along the Virginia barrier islands. During most years, knots arrived in early May, reached peak abundance during the third week of May, and were gone by mid-June. The peak period (10 May-3 June) accounted for >90% of detections for all years. The mean high count during the study was 7,373 AE 407 (SE). Decadal comparisons of high counts, accumulated numbers for the period of peak abundance and the season totals provided mixed results. Knots within the study area used peat banks and sandy beaches for foraging. Intertidal peat banks were patchily distributed and represented only 6% of the shoreline. Mean knot densities were comparable between the 2 habitats in the early period of migration but diverged rapidly such that by the third week of May, knot densities were 10-fold higher on peat compared to sand. Knots exhibited wide annual variation in habitat use; the number of knots observed on peat varied from 13% to 91% of the total birds for a given year, presumably reflecting the underlying population dynamics of respective bivalve populations. Potential prey dynamics coupled with the patchy distribution of peat appear to cause year-to-year variation in space use along the island chain. The Virginia barrier islands appear to be part of a terminal staging area for red knots that stretches from New Jersey south through the Outer Banks of North Carolina. Documenting red knot use within portions of this region beyond the well-studied Delaware Bay may lead to a more complete understanding of the sampling process used by red knots to make staging decisions. Ó 2014 The Wildlife Society.

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“…Both species breed in the Arctic with medium-to long-distance migrations and use Delaware Bay as a primary spring stopover. At this site, both red knot and ruddy turnstone primarily consume horseshoe crab eggs (Gillings et al 2007, Haramis et al 2007, Mizrahi and Peters 2009), although at other sites they consume a variety of invertebrate prey, including crustaceans, mollusks, polychaetes, and insects (Gonz alez et al 1996, Nettleship 2000, Baker et al 2001, Cohen et al 2010, Mart ınez-Curci et al 2015. Ruddy turnstone have a more diverse and opportunistic diet than red knot and will also scavenge carrion and human garbage (Gill 1986).…”

Section: Introductionmentioning

confidence: 99%

Foraging ecology mediates response to ecological mismatch during migratory stopover

et al. 2019

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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.

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The effect of benthic prey abundance and size on red knot (Calidris canutus) distribution at an alternative migratory stopover site on the US Atlantic Coast

Cited by 15 publications

References 33 publications

Sufficiency of horseshoe crab eggs for red knots during spring migration stopover in Delaware Bay USA

Sufficiency of horseshoe crab eggs for red knots during spring migration stopover in Delaware Bay USA

Spring migration of red knots along the Virginia barrier islands

Foraging ecology mediates response to ecological mismatch during migratory stopover

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