Department of Fisheries and Wildlife
 

Red Knot Stopover Ecology in the United States

Background and Rationale

The western Atlantic red knot is a long distance migrant that winters from Florida to the Tierra Del Fuego, and migrates to the Arctic to breed.  Many knots do this in long hops of several thousand kilometers.  In order to achieve these remarkable flights, they reduce the size of certain body organs and “fuel up” with large amounts of body fat which is burned during flight.

This subspecies has declined in recent years.  A key hypothesis that it is driven by a decline in horseshoe crab eggs, a key food for the red knot during its brief stopover on the Delaware Bay.  The goal of our red knot studies has been to further evaluate this hypothesis.  In 2004, we asked whether red knot distribution could be predicted by horseshoe crab egg distribution.  In 2005, we asked whether red knots and other shorebirds were depleting horseshoe crab eggs in the Delaware Bay.  In 2006 we began studying red knot stopover ecology on the Virginia barrier islands.


Project People



Jonathan Cohen
Research Scientist

Cohen

Jim Fraser
Co-PI

Sarah Karpanty
Co-PI

Dan Catlin
Cooperator, Virginia Tech

Barry Truitt
Cooperator, The Nature Conservancy

Bryan Watts
Cooperator, College of William and Mary

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Project Findings

Karpanty, Fraser, Berkson, Niles and Dey, and Smith 2006

  • The number of horseshoe crab eggs was the most important factor determining the use of Delaware Bay beaches by red knots
  • The knots shifted from peat-beaches to sandy Delaware Bay beaches when crab eggs became abundant,
  • While red knots used sandy beach zones more than expected, given their availability, 44% of red knot low tide locations were in bay and coastal emergent marsh.
  • The abundance of Donax variabilis and Mytilus edulis spat, both food for red knots, had a positive relationship with red knot use of sandy beaches.
  • These results are consistent with the hypothesis that the abundance of horseshoe crab eggs on sandy beaches is driving movement and distribution of red knots and that there is little alternative food during the migratory stopover in Delaware Bay.
  • Our findings that red knots disproportionately use Delaware Bay sites with abundant eggs support the continuation of management for sustained yield of horseshoe crabs and other food resources at this stopover.

(Cohen, Karpanty, Fraser, Watts, and Truitt 2009 in press Ė available August 2009) 

  • Stopover population sizes (±SE) in DENJ were 17,108 ± 1,322 in 2004 and 19,555 ± 831 in 2006 and in VA were 7,224 ± 389 in 2006 and 8,332 ± 718 in 2007, significantly greater than peak aerial counts.  
  • Years with similar peak counts had different residence probabilities; hence adjustments for turnover should be used in the future to assess annual population changes. 
  • Our results suggest that VA can support a significant portion of this red knot subspecies during migration in at least some years. 
  • Managing red knots for recovery should entail improving our understanding of the use of other Atlantic Coast sites and protecting key coastal habitat from disturbance and development. 

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