Passive recovery of an island bird community after rodent eradication
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The number and scale of island invasive species eradications is growing, but quantitative evidence of the conservation efficacy of passive recovery is limited. We compare relative abundances of breeding birds on Hawadax Island (formerly named Rat island), Aleutian Archipelago, Alaska, pre- and post- rat eradication to examine short-term (<1 year post-eradication) changes due to rodenticide application, and medium-term (5 years post-eradication) changes due to the absence of invasive rats. In the short term, Bald Eagle (Haliaeetus leucocephalus) numbers decreased from 24 individuals pre-eradication to two individuals <1 year post-eradication, but recovered to 10 individuals (42 % of pre-eradication) 5 years post-eradication, with all individuals nesting (63 % of the pre-eradication nesting). Five years post-eradication relative abundances of most terrestrial birds surveyed using point counts either significantly increased [Gray-crowned Rosy Finch (Leucosticte tephrocotis), Lapland Longspur (Calcarius lapponicus), Snow Bunting (Plectrophenax nivalis), Song Sparrow (Melospiza melodia)] or did not differ [Pacific Wren (Troglodytes troglodytes)]. Shorebirds also increased 5 years post-eradication with Black Oystercatchers (Haematopus palliates) increasing fivefold, and Rock Sandpiper (Calidris ptilocnemis) nesting increasing from one to five nests. We confirmed two species of ground nesting seabirds [Tufted Puffin (Fratercula cirrhata) and Leach’s Storm-petrel (Oceanodroma leucohoa)] as nesting (puffin) or engaged in courtship behavior (Storm-petrel) 5 years post-eradication. Our results indicate that despite the short-term impact on Bald Eagles, and without further human intervention, most terrestrial and marine birds have newly-colonized, re-colonized, or increased in abundance following the eradication of invasive rats.
KeywordsConservation Hawadax Island Invasive species Relative abundance Seabird Shorebird
We gratefully acknowledge field assistance provided by S. Abel, E. Bishop, A. Chateau, K. Cunningham, R. Dingler, S. Ebbert, C. Eggelston, R. Federer, J. Giffard, C. Hanson, R. Heinz, J. Helm, E. McCreless, A. McInturff, M. Mumm, K. Outten, R. Shaening-Pokrasso, and R. Stansbury. Alaska Maritime National Wildlife Refuge Staff, particularly V. Byrd, A. Sowls, S. Ebbert, G. Siekaniec and the crew of the R/V Tiglax provided invaluable research support. We were supported in part by the National Science Foundation (OPP-9985814), the National Fish and Wildlife Foundation (0101.12.030733) and the David and Lucile Packard Foundation. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the opinions or policies of the National Fish and Wildlife Foundation. Mention of trade names or commercial products does not constitute their endorsement by the National Fish and Wildlife Foundation.
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Conflict of interest
The authors declare that they have no conflict of interest.
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