Biol Invasions DOI 10.1007/s10530-015-1042-9 ORIGINAL PAPER Passive recovery of an island bird community after rodent eradication Donald A. Croll . Kelly M. Newton . Matthew McKown . Nick Holmes . Jeffrey C. Williams . Hillary S. Young . Stacey Buckelew . Coral A. Wolf . Gregg Howald . Milagra F. Bock . Jennifer A. Curl . Bernie R. Tershy Received: 13 August 2015 / Accepted: 18 December 2015 Ó Springer International Publishing Switzerland 2015 Abstract The number and scale of island invasive 5 years post-eradication, with all individuals nesting species eradications is growing, but quantitative (63 % of the pre-eradication nesting). Five years post- evidence of the conservation efficacy of passive eradication relative abundances of most terrestrial recovery is limited. We compare relative abundances birds surveyed using point counts either significantly of breeding birds on Hawadax Island (formerly named increased [Gray-crowned Rosy Finch (Leucosticte Rat island), Aleutian Archipelago, Alaska, pre- and tephrocotis), Lapland Longspur (Calcarius lapponi- post- rat eradication to examine short-term (\1 year cus), Snow Bunting (Plectrophenax nivalis), Song post-eradication) changes due to rodenticide applica- Sparrow (Melospiza melodia)] or did not differ tion, and medium-term (5 years post-eradication) [Pacific Wren (Troglodytes troglodytes)]. Shorebirds changes due to the absence of invasive rats. In the also increased 5 years post-eradication with Black short term, Bald Eagle (Haliaeetus leucocephalus) Oystercatchers (Haematopus palliates) increasing numbers decreased from 24 individuals pre-eradica- fivefold, and Rock Sandpiper (Calidris ptilocnemis) tion to two individuals \1 year post-eradication, but nesting increasing from one to five nests. We recovered to 10 individuals (42 % of pre-eradication) confirmed two species of ground nesting seabirds D. A. Croll (&) Á K. M. Newton Á M. McKown Á H. S. Young M. F. Bock Á B. R. Tershy Department of Ecology, Evolution and Marine Biology, Coastal Conservation Action Lab, University of University of California, Santa Barbara, 2116 Noble Hall, California Santa Cruz, 100 Shaffer Rd., Santa Cruz, Santa Barbara, CA 93106, USA CA 95060, USA e-mail: [email protected] S. Buckelew Kachemak Bay Research Reserve, 95 Sterling Highway, M. McKown Suite 2, Homer, AK 99603, USA Conservation Metrics Inc., 100 Shaffer Rd., Santa Cruz, CA 95060, USA J. A. Curl Wildlife Biology and Conservation, University of Alaska N. Holmes Á C. A. Wolf Á G. Howald Fairbanks, Fairbanks, AK 99775, USA Island Conservation, 2161 Delaware Ave. Suite A, Santa Cruz, CA 95060, USA J. C. Williams Alaska Maritime National Wildlife Refuge, US Fish and Wildlife Service, 95 Sterling Highway, Suite 1, Homer, AK 99603, USA 123 D. A. Croll et al. [Tufted Puffin (Fratercula cirrhata) and Leach’s eradicating all invasive alien species on an island, and Storm-petrel (Oceanodroma leucohoa)] as nesting limited post-eradication monitoring. Moreover, (puffin) or engaged in courtship behavior (Storm- Kappes and Jones (2014), recently suggested the need petrel) 5 years post-eradication. Our results indicate to evaluate the necessity of active versus passive that despite the short-term impact on Bald Eagles, and restoration programs following invasive mammal without further human intervention, most terrestrial eradication. In this paper we document passive recov- and marine birds have newly-colonized, re-colonized, ery of bird communities following a rodent eradication or increased in abundance following the eradication of in autumn 2009 on Hawadax Island (formerly Rat invasive rats. Island), Aleutian Archipelago, Alaska. The Aleutian Archipelago has 299 bird species, 80 Keywords Conservation Á Hawadax Island Á of which (27 %) are residents or migratory breeders, Invasive species Á Relative abundance Á Seabird Á including 26 seabird species (Gibson and Byrd 2007). Shorebird The archipelago had no terrestrial mammals west of Umnak Island until Arctic foxes (Alopex lagopus) were intentionally introduced by fur ranchers and Introduction Norway rats (Rattus norvegicus) were accidentally introduced on several islands, including Hawadax Islands make up roughly 5 % of the Earth’s land area, Island, in the 1700s (Bailey 1993). In the Aleutians, yet host a disproportionate amount of global biodiver- fox and rat predation reduces abundance of nesting sity including 19 % of all bird species (Tershy et al. birds (particularly seabirds) (Bailey 1993; Ebbert and 2015). Unfortunately, island breeding birds are dis- Byrd 2002; Byrd et al. 2005; Major et al. 2006), proportionately threatened, accounting for 95.3 % of potentially decreases abundance of non-breeding recent historical (since 1500) avian extinctions (Loehle birds, and can indirectly alter community processes and Eschenbach 2012). A primary cause of insular and structure (e.g. intertidal and plant communities) avian extinctions is introduced alien species (Clavero (Croll et al. 2005; Kurle et al. 2008). On Hawadax et al. 2009), with invasive rodents in the genera Rattus Island, the combined impacts of introduced foxes and among the most damaging invasive animals to island- rats were likely significant, due to the synergistic breeding birds (Towns et al. 2006; Howald et al. 2007). effects from a carnivore and an omnivore as well as Invasive rodents have invaded *90 % of the world’s the potential for apparent competition between rats archipelagos (Jones 2010), but can be eradicated from and native birds mediated by fox hyperpredation (the many islands, with over 700 successful operations presence of an alternate prey leads to an impact of the globally (Keitt et al. 2011; DIISE 2015). predator on the prey via an elevated density of the While there is compelling evidence that invasive predator) on native birds (reviewed in Russell 2011; alien species have a broad range of direct and indirect Towns et al. 2011). Foxes were successfully eradi- impacts on island ecosystems (e.g. Croll et al. 2005; cated in 1984 (Bailey 1993), but invasive rats Jones et al. 2008; Kurle et al. 2008; Towns et al. 2006), persisted and apparently limited avian recovery and the number and scale of eradication efforts is compared to surrounding islands from which foxes growing (Keitt et al. 2011), quantitative evidence of the were eradicated (J. Williams, pers. obs.). Rats were efficacy of eradication as a tool for avian conservation eradicated using an aerial broadcast of cereal grain on islands is surprisingly limited (Jones 2010). pellets containing rodenticide (Brodifacoum) in Regional reviews document benefits for native species September–October 2008 with an overall goal of on French (Lorvelec and Pascal 2005) and New ‘‘improving habitat quality for native species’’ (US Zealand (Bellingham et al. 2010) islands, and a review Fish and Wildlife Service 2007). Details on the by Lavers et al. (2010) demonstrated that bird demo- eradication and eradication confirmation are presented graphic parameters respond positively to rodent erad- in Buckelew et al. (2011). Here we compare relative ications. In addition, Towns et al. (2006) documented abundances of Hawadax breeding birds pre- and post- plant and animal recovery from eradications, but rat eradication to examine (1) short-term changes that commented that the evidence was complicated by lack may be due to the application of rodenticide (\1 year of pre-eradication data, confounding effects of not post-eradication), and (2) medium-term changes that 123 Passive recovery of an island bird community 170° E 180° -170° W -160° W 60° N 60° N Alaska 55° N 55° N Aleutian Island Archipelago 018036090 Miles 170° E Rat Islands Group 180° -170° W -160° W 178° E 179° E 178.2° E 178.3° E 178.4° E Rat Islands Group Hawadax Island Kiska 52° N 52° N Semisopochnoi Hawadax 51.8° N 51.8° N Amchitka 0204010 Miles 02.551.25 Miles 178° E 179° E 178.2° E 178.3° E 178.4° E Fig. 1 The location of Hawadax Island in the Rat Islands Group, central Aleutian Island Archipelago, Alaska, USA may be due to the absence of invasive rats (5 years largest of which is *4 ha and \1 km offshore. Rat post-eradication). eradication was conducted after the end of seasonal bird breeding activities, when food resources for rats were limited (Buckelew et al. 2011). Methods To evaluate the impacts of the rat eradication on island bird populations we conducted a variety of Hawadax Island (51.80°N, 178.30°E) (known as Rat surveys in May–June to coincide with seasonal breed- Island until renamed in 2012; U.S. Board on Geo- ing activities of native birds. The range of survey types graphic Names 2012) is located in the Rat Islands utilized were selected to provide a robust index of group in the western Aleutian Islands and part of the changes in abundance of all major groups of birds that Alaska Maritime National Wildlife Refuge (Fig. 1). commonly occur on the island, and to detect changes in The 2780 ha island has steep coastal cliffs along the presence of rare species. For some species we censused majority of the coastline backed by rolling hills and entire island populations (e.g. Bald Eagles (Haliaeetus plateaus, with nine small clusters of lakes and no leucocephalus), Peregrine Falcons (Falco peregrinus), human inhabitants. The interior contains a small range Glaucous-winged Gull (Larus glaucescens) nests). of mountains with a peak elevation of 400 m. There However, due to difficulties inherent in measuring are more than 30 offshore rock stacks and islets, the absolute abundance in highly mobile species with 123 D. A. Croll et al.