Flesh-footed Shearwater burrows on Lord Howe Island, photograph by Ian Hutton

Chris Wilcox (CSIRO Oceans and Atmosphere, Hobart, Tasmania, Australia) and colleagues have published open access in the journal Scientific Reports on assessing threats facing Flesh-footed Shearwater Ardenna carneipes (Near Threatened) ashore on Lord Howe Island.

The paper’s abstract follows:

“Globally, seabird populations have been in decline due to multiple threats throughout their range. Separating simultaneous pressures is challenging and can require significant amounts of data over long periods of time. We use spatial contrasts to investigate the relative importance of several drivers for the purported decline in a species listed as in decline as an example species, the Flesh-footed shearwater (Ardenna carneipes). On Lord Howe Island in the Tasman Sea, Australia, this seabird suffers from habitat loss due to housing development, intensive mortality in fisheries, plastic ingestion, and roadkill due to vehicular traffic on its breeding island. We repeated a quantitative survey of the population to ascertain whether the decline previously reported had continued and to evaluate the purported mortality sources (Reid et al. in PLoS ONE 8(4):e58230, 2013, Lavers et al. in Global Ecol Conserv 17:e00579, 2019). We measured burrow density, area of occurrence, occupancy and breeding success, integrating them with previous surveys using a Bayesian statistical model to generate longer term estimates of demographic rates. We used spatial patterns to test whether mortality on roads or proximity to human habitation was influencing population demographics. In contrast to predictions, we found the population had stabilised or increased. Characteristics such as burrow occupancy and breeding success showed little pattern, with weak evidence for impacts from road mortality and housing development. Such a data-rich approach is substantially more informative and can better support seabird conservation and management efforts does require more field-time and additional equipment than most contemporary surveys, the data is substantially more informative and can better clarify the results of efforts in seabird conservation and management.”

A Flesh-footed Shearwater pair in a breeding colony on Lord Howe Island, photograph by Ian Hutton

Reference:

Wilcox, C., Carlile, N., Hardesty, B.D. & Reid, T. 2021.  Assessing multiple threats to seabird populations using flesh-footed shearwaters Ardenna carneipes on Lord Howe Island, Australia as case study. Scientific Reports doi.org/10.1038/s41598-021-86702-4.

John Cooper, ACAP Information Officer, 16 April 2021

"Seabird Sunset", acrylics by Kitty Harvill, after a photograph by Dimas Gianuca

Caitlin Frankish (British Antarctic Survey, Cambridge, UK) and colleagues have published open access in the journal Aquatic Conservation: Marine and Freshwater Ecosystems on diving behaviour of White‐chinned Petrel Procellaria aequinoctialis (Vulnerable).

The paper’s abstract follows:

Many seabirds dive to forage, and the ability to use this hunting technique varies according to such factors as morphology, physiology, prey availability, and ambient light levels. Proficient divers are more able to seize sinking baits deployed by longline fishing vessels and may return them to the surface, increasing exposure of other species. Hence, diving ability has major implications for mitigating incidental mortality (bycatch) in fisheries.

Here, the diving behaviour and activity patterns of the most bycaught seabird species worldwide, the white‐chinned petrel (Procellaria aequinoctialis), tracked from Bird Island (South Georgia), are analysed. Three data sources (dives, spatial movements, and immersion events) are combined to examine diverse aspects of at‐sea foraging behaviour, and their implications for alternative approaches to bycatch mitigation are considered.

The tracked white‐chinned petrels (n = 14) mostly performed shallow dives (<3 m deep) of very short duration (<5 s), predominantly during darkness, but only 7 and 10% of landings in daylight and darkness, respectively, involved diving, suggesting that surface‐seizing is the preferred foraging technique. Nonetheless, individuals were able to dive to considerable depth (max = 14.5 m) and at speed (max = 2.0 m·s−1), underlining the importance of using heavy line‐weighting to maximize hook sink rates, and bird‐scaring lines (Tori lines) that extend for long distances behind vessels to protect hooks until beyond diving depths.

With thanks to Richard Phillips.

Reference:

Frankish, C.K., Manica, A., Navarro, J. & Phillips, R.A. 2021.  Movements and diving behaviour of white‐chinned petrels: diurnal variation and implications for bycatch mitigation.  Aquatic Conservation: Marine and Freshwater Ecosystems https://doi.org/10.1002/aqc.3573.

John Cooper, ACAP Information Officer, 15 April 2021

(a), (b) Broad-billed Prion eggshells with teeth marks from Black Rats in Hillpiece Cave, Tristan da Cunha, (c) incubating prions, with an abandoned whole egg in the background, (d) Black Rat harassing a small prion chick (from the publication)

Ben Dilley (FitzPatrick Institute of African Ornithology, University of Cape Town, South Africa) and colleagues have published in the journal Ostrich Journal of African Ornithology on the suspected role played by rats in low breeding success of Broad-billed Prions Pachyptila vittata on Tristan da Cunha.

The paper’s abstract follows in English and French:

Tristan da Cunha is a 96 km² volcanic island in the South Atlantic Ocean. Black Rats Rattus rattus reached the island from a shipwreck in 1882 and their depredation of seabirds’ eggs and chicks are likely partly responsible for the much lower densities of burrow-nesting petrels, compared with adjacent rodent-free islands in the archipelago. We monitored a colony of Broad-billed Prions Pachyptila vittata breeding in a coastal cliff cave in 2015/2016, where a maximum of 6% of chicks survived from 310 nests. We suspect rats frequently depredated eggs (36% of eggs were found broken with rat bite marks) and infrared trail cameras recorded how rats repeatedly hassled chicks, although no direct chick depredations were recorded.

Tristan da Cunha est une île volcanique de 96 km² localisée en océan Atlantique sud. Le rat noir Rattus rattus colonisa l’île en 1882 après le naufrage d’un navire. La predation du rat sur les oeufs et oisillons d’oiseaux marins est très probablement responsable de la très faible densité de Procellariidées nichant en terrier comparé à d’autres îles dépouvues du rongeur au sein de l’archipel. Nous avons suivi une colonie de Prion de Forster Pachyptila vittata nichant sur une falaise cotière au sein d’une grotte en 2015/2016. Seulement 6% des oisillons survécurent sur les 310 nids suivis. Nous suspectons que les rats prédatent fréquemment les oeufs (36% des oeufs ont été retrouvés cassés avec des traces de morsures de rats). Aussi, les cameras infrarouge sur les sentiers ont enregistré une incessante aggression des rats sur les oisillons, bien qu’aucune predation directe ne fut enregistrée.”

Although a draft operational plan to eradicate Tristan’s rodents was produced in 2007, there are apparently no current plans to eradicate them.  However, local control of rodents utilizing bait stations occurs in inhabited and cultivated areas.  In contrast, an attempt to eradicate introduced House Mice on Gough Island, part of the Tristan da Cunha group of islands, is set to occur this austral winter (click here).

With thanks to Ben Dilley.

References:

Brown, D. 2007.  Preliminary Operational Plan for Rodent Eradication from Tristan da Cunha.  Unpublished Report to the Royal Society for the Protection of Birds.  Sandy: Royal Society for the Protection of Birds.  115 pp.

Dilley, B.J., Davies, D., Repetto, J., Swain, G. & Ryan, P.G. 2020.  Rats and prions at Tristan da Cunha Island.  Ostrich  91(3). 

John Cooper, ACAP Information Officer, 14 April 2021

Balearic Shearwater at sea, photograph by Pep Arcos

Isabel Afán (Remote Sensing and GIS Laboratory, Estación Biológica de Doñana, Seville, Spain) and colleagues have published in the journal Marine Biology on tracking chick-rearing Balearic Shearwater Puffinus mauretanicus (Critically Endangered) at sea in relation to environmental factors.

The paper’s abstract follows:

“Foraging distribution of flying seabirds is constrained by environmental factors influencing individual decision-making. This must be particularly true during the breeding period, when individuals face additional limitations imposed by their central-place foraging behaviour. We used GPS data loggers and Argos PTTs to track the foraging flights of Balearic shearwaters (Puffinus mauretanicus) during the chick-rearing period of 2011–2014 in the Balearic Islands (Western Mediterranean).  We identified main areas used by tracked birds and characterised their productivity patterns. Based on a spatial seascape approach of flight costs varying with time, shaped by environmental processes as winds, we also estimated flight costs to reach foraging grounds in outward and return trips from the colony. Individuals repeatedly used the closest areas on the Iberian continental shelf. However, sporadic and favourable wind conditions facilitated low-cost flight to more distant and equally productive areas of the western North African shelf.”

With thanks to Pep Arcos.

Reference:

Afán, I., Arcos, J.M., Ramírez, F., García, D., Rodríguez, B. Delord, K., Boué, A.,·Micol, T., Weimerskirch, H. & Louzao, M. 2021.  Where to head: environmental conditions shape foraging destinations in a critically endangered seabird.  Marine Biology 168. doi.org/10.1007/s00227-021-03830-1.

John Cooper, ACAP Information Officer, 13 April 2021