Anticoagulant Residual Concentration and Poisoning in Birds Following a Large-Scale Aerial Application of 25 ppm Brodifacoum Bait for Rat Eradication on Rat Island, Alaska

Abstract

To eradicate invasive Norway rats, an aerial broadcast of the rodenticide Brodifacoum-25W Conservation was conducted on 2,777-ha Rat Island, within the Aleutian Islands Unit of Alaska Maritime National Wildlife Refuge, between 29 September and 5 October 2008. During subsequent visits to Rat Island (in spring and fall 2009) to check for evidence of remaining rats and to look for evidence of nontarget mortality, personnel found an unexpectedly high number of dead birds: more than 420 carcasses, mostly glaucous-winged gulls and bald eagles, but also included 24 other species. Some carcasses had tissue suitable for analysis and were collected. Seventy bird carcasses were necropsied and cause of death was determined for 50 birds; 45 died of brodifacoum toxicosis. Necropsy determined almost all gulls and eagles had extensive hemorrhaging, consistent with brodifacoum poisoning. All eagles and all but 1 gull tested positive for brodifacoum residues. Positive tests for brodifacoum also were recorded for single specimens of emperor goose, northern fulmar, pelagic cormorant, peregrine falcon, rock sandpiper, and gray-crowned rosy finch. Two Lapland longspurs tested positive for exposure to brodifacoum. Nontarget bird mortality from brodifacoum exposure at Rat Island was higher than predicted in the Environmental Assessment.

A review: poisoning by anticoagulant rodenticides in non-target animals globally

“…Of these, 19 papers report poisoning of raptors. There are six publications from the U.S.A. [9, 42, 45, 48,49,50], three from Canada [1, 18, 55], nine from the U.K. [7, 19, 31, 46, 47, 58,59,60,61], two from France [13, 25], three from Spain [28, 43, 44], two from Denmark [5, 11], one from Norway [26], and four from New Zealand (NZ) [6, 8, 14, 35]. These reports and the proposed exposure pathways are summarized below.…”

“…Altogether, there were 2,694 out of 4,891 individuals (55%) of non-target animals have been reported to have AR residues in their livers between 1981 and 2013 [1, 5,6,7,8,9, 11, 13, 14, 18, 19, 25, 26, 28, 31, 35, 42,43,44,45,46,47,48,49,50, 55, 58,59,60,61](A)FGARsSGARsWarfarinCouma-tetralylDipha-cinoneChloro-phacinoneBrodi-facoumBroma-dioloneDifen-acoumDifeti-aloneFlocou-mafenDetection rate (%)1.04.55.05.631.030.026.05.05.7The number of detection27108991131,4651,3461,048101175The number of analysis2,6392,3911,972…”

Non-target species mortality and the measurement of brodifacoum rodenticide residues after a rat (Rattus rattus) eradication on Palmyra Atoll, tropical Pacific

“…data). Therefore, having all sampled mullet contaminated with brodifacoum, and their status as a common prey item, reveals the high probability that such a terrestrial operation of attempted rat eradication can have bottom up effects in tropical marine food webs (Ebbert and Burek-Huntington, 2010). Thus, the exposure risk to other marine organisms and indirect effects to birds should be considered in future applications.…”

“…No additional monitoring occurred after the broadcast because winter weather excluded crews from the island. The next spring, 423 dead birds of 26 species were collected including 320 glacous-winged gulls (Larus bachmani) and 46 bald eagles (Haliaeetus leucocephalus) (Ebbert and Burek-Huntington, 2010). Of the 36 bird carcasses from nine species tested for residues, 35 carcasses had detectable brodifacoum residues.…”

“…A number of studies have analyzed non-target species for anticoagulant residues following rodenticide operations that are conducted for biological conservation purposes (e.g., Dowding et al, 1999;Dunlevy and Swift, 2010;Howald et al, 1999Howald et al, , 2009Masuda et al, 2014;Ogilvie et al, 1997;Pitt et al, 2005). Furthermore, residues from brodifacoum can move through the local food web and persist in the environment for unknown periods (e.g., Dowding et al, 2006;Ebbert and Burek-Huntington, 2010;Primus et al, 2005). Clearly the need is great to understand the environmental and non-target effects from rodenticide use for conservation purposes.…”