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California Gull Predator Management and Reproductive Success of Endangered California Least Terns in the San Francisco Bay, California

  • Author(s): Riensche, David L.
  • Kitting, Christopher L.
  • Groff, Tierra C.
  • Dulava, Sharon
  • Bell, Douglas A.
  • et al.
Abstract

Gull predation is known to be an important source of egg and chick mortality for many waterbirds and can have severe impacts on recovery efforts for special status species. We evaluated the effectiveness of California gull management and removal by monitoring tern hatching and fledgling success annually. From 2005 to 2011, nesting success was monitored at a newly established California least tern colony at Hayward Regional Shoreline in San Francisco Bay. No gull management was undertaken prior to 2007. California gulls were the most abundant aerial predator (97%). We recorded 3,769 predatory gull-tern interactions and presumptive take of 26 tern eggs and 23 chicks. Although gull predatory behavior did not change statistically, gull management efforts resulted in significantly improved tern breeding success (measured by number of nests, eggs, chicks, and fledglings). From 2007 to 2011, this colony produced a total of 242 successful nests and 291 fledglings, an average nesting density of 196 nests per ha, and an average of 1.07 fledglings per breeding pair. We discuss difficulties of lethal control of predators, and suggest the importance of human presence for reducing gull predation at the site.

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