Delia Davies

Effects of mouse predation on burrowing petrel chicks at Gough Island

Abstract Since 2004 there has been mounting evidence of the severe impact of introduced house mice (Mus musculus L.) killing chicks of burrow-nesting petrels at Gough Island. We monitored seven species of burrow-nesting petrels in 2014 using a combination of infra-red video cameras augmented by burrowscope nest inspections. All seven camera-monitored Atlantic petrel (Pterodroma incerta Schlegel) chicks were killed by mice within hours of hatching (average 7.2±4.0 hours) with an 87% chick failure rate (n=83 hatchlings). Several grey petrel (Procellaria cinerea Gmelin) chicks were found with mouse wounds and 60% of chicks failed (n=35 hatchlings). Video surveillance revealed one (of seven nests filmed) fatal attack on a great shearwater (Puffinus gravis O’Reilly) chick and two (of nine) on soft-plumaged petrel (Pterodroma mollis Gould) chicks. Mice killed the chicks of the recently discovered summer-breeding MacGillivray’s prion (Pachyptila macgillivrayi Mathews), with a chick mortality rate of 82% in 2013/14 and 100% in 2014/15. The closely-related broad-billed prion (P. vittata Forster) breeds in late winter and also had a chick mortality rate of 100% in 2014. The results provide further evidence of the dire situation for seabirds nesting on Gough Island and the urgent need for mouse eradication.

Giant petrels as predators of albatross chicks

Giant petrels Macronectes spp. are not thought to be important predators of albatross chicks, although they are known to kill pre-fledging Thalassarche and Phoebetria albatrosses. We report the first records of predation of healthy great albatross Diomedea spp. chicks, killing wandering albatrosses D. exulans at night on sub-Antarctic Marion Island. Breeding success of this species has decreased markedly in the area where attacks occurred, suggesting that giant petrel predation events are a recent phenomenon. Mouse attacks on wandering albatross chicks may have contributed to the development of this hunting technique. We also report the first observations of giant petrel predation on pre-fledging grey-headed albatross T. chrysostoma chicks as well as additional records of sooty albatross P. fusca chicks being targeted. Only adult northern giant petrels M. halli have been confirmed to kill albatross chicks on Marion Island. Given the threatened status of wandering albatrosses, and the importance of Marion Island for this species, monitoring of their breeding success is necessary to assess whether the predation of chicks by giant petrels spreads around the island.

The distribution of breeding Sooty Albatrosses from the three most important breeding sites: Gough, Tristan and the Prince Edward Islands

ABSTRACT Sooty Albatrosses (Phoebetria fusca; Endangered) breed only on sub-Antarctic islands in the South Atlantic and south-west Indian Oceans, with most of the population at Gough Island (≈37%), the Prince Edward Islands (≈24%) and the Tristan da Cunha archipelago (≈20%). Breeding Sooty Albatrosses from all three of these populations were tracked during the incubation and brood-guard periods. Birds from Marion Island (Prince Edwards) ranged farther north, despite being the most southerly of the three study sites. Tristan-Gough Sooty Albatrosses concentrated mostly around the Sub-Antarctic Front (SAF) in the southern Atlantic Ocean, whereas Marion birds were associated with both the SAF and the Sub-Tropical Front (STF) in the southern Indian Ocean. Our tracking data describe where 80% of breeding Sooty Albatrosses forage during the incubation and brood-guard period, including the first records of birds from Marion and Tristan. Such data are important to identify key areas where these threatened birds need protection from mortality on long-line fishing gear. Overlap with the distribution of tuna long-line effort was greater for Sooty Albatrosses from Tristan da Cunha and Gough Island than for Marion birds, suggesting that birds breeding at Atlantic colonies might be at greater risk of bycatch mortality in this fishery.

The distribution and abundance of Blue Petrels (Halobaena caerulea) breeding at subantarctic Marion Island

ABSTRACT Blue Petrels (Halobaena caerulea) are known to breed at seven locations in the Southern Ocean. Population estimates have been made recently for the two major breeding sites, but accurate estimates are lacking for the remaining locations. We used a systematic survey technique to estimate the size of the population breeding at Marion Island (290 km2), the larger of the two Prince Edward Islands. A combination of colony area and density estimates suggested there were 214 700 Blue Petrel burrows on Marion Island in 2012. Burrow occupancy rates at the mid-incubation stage averaged 82% (range 36–98%), suggesting a total breeding population of 145 000 pairs (95% confidence interval 110 000–180 000). There appeared to be some range expansion since the population was mapped in the mid-1980s. Predation of chicks and eggs by introduced house mice (Mus musculus) could be affecting the recovery of Blue Petrels since feral cats (Felis catus) were eradicated in 1991. Based on our count from Marion Island alone, the Prince Edward Islands support the third largest population of Blue Petrels globally, after Diego Ramirez Islands and the Kerguelen Islands.

Diving behaviour of Grey Petrels and its relevance for mitigating long-line by-catch

Abstract The Grey Petrel (Procellaria cinerea) is listed as Near Threatened globally owing to incidental mortality on long-line fishing gear and reduced breeding success on islands caused by the introduction of alien predators. However, there are few studies of its foraging ecology and none of its diving behaviour. We obtained data from temperature-depth recorders (n = 7 birds) and global positioning satellite trackers (n = 15) deployed on Grey Petrels breeding on Gough Island, South Atlantic Ocean. Most birds foraged in the productive oceanic waters west or north-west of South Georgia. Average maximum dive-depth was 3.2 ± 2.2 m with most dives <5 m (85%) and 95% of dives <7 m deep. The maximum dive-depth (22 m) was deeper than previous measurements of dive-depth in Procellaria petrels, and maximum dive-duration also was longer than previously recorded in Procellaria petrels (at least 39 s). Individuals varied greatly in the mean number of dives per day (range 0.4-24.5). Sex did not influence depth or duration of dives but sample sizes were small. The time of day influenced dive-depth, and dives during daylight were, on average, deeper than dives at night, but the effect was weak; the maximum dive-depth at night was 17 m. By providing insights into the diving behaviour of Grey Petrels our findings help to explain their high mortality on fishing long-lines. We suggest that fisheries adopt bird-scaring lines that protect long-lines from scavenging seabirds during the setting process to a depth of at least 10 m, which could be achieved by increasing line-weighting or modifying bird-scaring lines, or both. An understanding of the foraging ecology of commonly recorded by-catch species, such as Grey Petrels, is essential in the design of future devices to mitigate seabird by-catch in long-line fisheries.

Trapping and capture myopathy in Ludwig's Bustard

Banding and deploying tracking devices are important techniques to study birds of conservation concern, but require that individuals can be safely and efficiently caught and handled. We describe the trapping techniques used to catch Ludwigs Bustards (Neotis ludwigii) in the Karoo, South Africa, for a satellite tracking programme aiming to better understand the movement biology of this poorly known and threatened bird. Trapping sites on transformed land used as congregation sites were difficult to locate for these nomadic and partially migratory birds, but six of nine prospective trapping trips were successful. Although labour-intensive, extensive deployment of leg nooses coupled with guide-lines to direct birds proved effective. We caught 12 bustards at four sites across the Karoo over 37 trapping days in 2010–2012. Success was male-biased, with only two females caught. Noose traps were safe, with no injuries to captured birds. However, in common with other studies, we encountered problems with capture myopathy after handling five bustards; two subsequently died and three recovered.We designed a ‘harnessing chair’ to reduce the risk of capture myopathy, but still encountered problems. We recommend noose traps with guide-lines to catch other large, wary birds in open environments where there is some predictability of habitat use,but caution against long handling times and trapping in extreme temperatures.