Cattle egrets regurgitate house mouse carcasses onto a mouse-free island: implications for rodent eradications

Context. Eradication of invasive rodents on islands typically results in positive conservation gains, and maintaining a rodent-free island requires elevated biosecurity, including prevention of assisted rodent arrival via watercraft, aircraft and animals such as birds. Cattle egrets (Bubulcus ibis) are widespread, and often fly several kilometres daily to roost and forage. They frequently swallow insects and vertebrates (including rodents) whole, and some regurgitate prey. Cattle egrets have been regularly observed flying between the Hawaiian Islands of Ni’ihau (where non-native mice and rats are established) and Lehua (where one species of non-native rat is established and was targeted during a recent eradication attempt). Aims. The objectives were to identify the species of rodent that cattle egrets regurgitate following transport between Ni’ihau and Lehua islands, and to determine if any of the rodent individuals regurgitated were alive once deposited onto Lehua Island following 1.1-km oversea flights. Methods. Eighty-five individual rodent carcasses (regurgitated by cattle egrets) were collected, preserved and identified to species using morphological characteristics and DNA sequencing. Key results. All rodents regurgitated by cattle egrets were dead upon collection on Lehua Island. Although the Pacific rat (Rattus exulans) is the only rodent species on Lehua Island, and field staff suspected the regurgitated rodents were R. exulans, all 85 carcasses were identified as house mice (Mus musculus). Conclusions. This is the first evidence (that the authors know of) showing movement of rodent carcasses, via cattle egrets, between islands. Implications. Cattle egrets that deposit rodent carcasses onto rodent-free islands, or segments of islands, may confuse land managers and biosecurity professionals who are unaware of this phenomenon. House mice did not survive cattle egret ingestion,.1-km flight and regurgitation; therefore it is unlikely that live rodents would be introduced to rodent-free areas via cattle egrets

Cattle egrets regurgitate house mouse carcasses onto a mouse-free island: implications for rodent eradications

Context. Eradication of invasive rodents on islands typically results in positive conservation gains, and maintaining a rodent-free island requires elevated biosecurity, including prevention of assisted rodent arrival via watercraft, aircraft and animals such as birds. Cattle egrets (Bubulcus ibis) are widespread, and often fly several kilometres daily to roost and forage. They frequently swallow insects and vertebrates (including rodents) whole, and some regurgitate prey. Cattle egrets have been regularly observed flying between the Hawaiian Islands of Ni’ihau (where non-native mice and rats are established) and Lehua (where one species of non-native rat is established and was targeted during a recent eradication attempt). Aims. The objectives were to identify the species of rodent that cattle egrets regurgitate following transport between Ni’ihau and Lehua islands, and to determine if any of the rodent individuals regurgitated were alive once deposited onto Lehua Island following 1.1-km oversea flights. Methods. Eighty-five individual rodent carcasses (regurgitated by cattle egrets) were collected, preserved and identified to species using morphological characteristics and DNA sequencing. Key results. All rodents regurgitated by cattle egrets were dead upon collection on Lehua Island. Although the Pacific rat (Rattus exulans) is the only rodent species on Lehua Island, and field staff suspected the regurgitated rodents were R. exulans, all 85 carcasses were identified as house mice (Mus musculus). Conclusions. This is the first evidence (that the authors know of) showing movement of rodent carcasses, via cattle egrets, between islands. Implications. Cattle egrets that deposit rodent carcasses onto rodent-free islands, or segments of islands, may confuse land managers and biosecurity professionals who are unaware of this phenomenon. House mice did not survive cattle egret ingestion,.1-km flight and regurgitation; therefore it is unlikely that live rodents would be introduced to rodent-free areas via cattle egrets

Update on the status of the avifauna of Lehua Islet, Hawai'i, including initial response of seabirds to rat eradication

Reports were scanned in black and white at a resolution of 600 dots per inch and were converted to text using Adobe Paper Capture Plug-in.Lehua Islet is a small volcanic islet located 1 km north of Ni‘ihau, protected by the State of Hawai‘i as a Seabird Sanctuary because of its large seabird colonies. Between December 2011 and May 2021, data was collected using a variety of methods to provide an update of the islet’s avifauna, with a particular focus on seabirds. In 2017 a rat eradication project was undertaken to remove the Polynesian Rat Rattus exulans and the islet was officially declared rat free on 20 April 2021. This report therefore provides both an update on the status of the avifauna of Lehua and an assessment of the initial impact of the rat eradication project on breeding seabirds. A total of 39 bird species were recorded on Lehua over the study period, including 18 seabird species (9 confirmed breeding). The most numerous breeding seabird was the Wedge-tailed Shearwater Ardenna pacifica, estimated at 22,226 ± 2,981bp. Lehua is therefore an important refuge for this species, which suffers significant predation by cats and dogs across the Main Hawaiian Islands. Several species, particularly burrow-nesting seabirds, responded positively to rat eradication. The most dramatic changes occurred in the Bulwer’s Petrel Bulweria bulwerii breeding population. This species was rarely encountered before eradication, but numbers of burrows located, the percentage of burrows where adults were confirmed breeding and two measures of nest success increased after eradication. Wedge-tailed Shearwaters also responded positively, with Mayfield Nest Success Estimates significantly higher in the three years after rats were eradicated than in the two years before eradication (t=2.37, p=0.02). Conversely, one species - the endangered Band-rumped Storm-petrel Oceanodroma castro - appeared to decline after rat eradication (as measured via call rates on acoustic sensors), although the change was not significant. Rat eradication has been a critical milestone in the conservation of Lehua Islet, and further natural recovery of seabirds can be expected. Future management actions will be key for capitalizing on the early successes of the rat eradication project. These include social attraction of seabirds that have been extirpated from the islet and habitat restoration through invasive plant removal and outplanting of native species. Regular control of the two remaining non-native predators (Barn Owl Tyto alba and Cattle Egret Bubulcus ibis) on the islet by well-trained predator control specialists will also be critical, as Barn Owls could reverse conservation gains and prevent new seabird species from colonizing. Lastly, ensuring a rigorous biosecurity program and monitoring strategy is vital to prevent reinvasion