Search

Nocturnal burrow-nesting seabirds are notoriously difficult to study and can go unnoticed for years in remote areas. One of these species is the Common Diving Petrel Pelecanoides urinatrix, which has a circumpolar breeding distribution in the Southern Ocean, including at the sub-Antarctic Prince Edward Islands. At Marion Island, the larger of the two islands, the species was extirpated by cats that were introduced in 1948. The cats were eradicated by 1991, and Common Diving Petrels were discovered in burrows in coastal Poa cookii (Cook's tussock grass) on a steep south-facing slope in Goodhope Bay during April 2015. Subsequent surveys in October 2015 and February 2016 confirmed breeding over a 1-ha area. In 2019/2020, breeding phenology and success was studied in 36 nests at the same site. Birds called from their burrows from mid-September, laying started in early October, and the first chick was observed on 20 December. Hatching peaked in early January and chicks fledged from the end of February to mid-March. This breeding phenology is similar to that at the neighbouring Crozet Archipelago. Overall nest survival was 46.4 ± 9.2% (mean ± SE; 95% CI: 29.5–64.1%), with most failures happening around hatching time. Further monitoring is needed to assess whether introduced House Mice Mus musculus contributed to the low hatching success. Common Diving Petrels were discovered breeding in other coastal areas, mostly in the south and east of the island. It is unlikely that breeding by this species was overlooked for three decades, suggesting that the elimination of cats allowed Common Diving Petrels to recolonise the island. [ABSTRACT FROM AUTHOR]

Copyright of Ostrich: The Journal of African Ornithology is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Determining the migratory status of seabird populations is crucial for addressing conservation concerns. The Roseate Tern Sterna dougallii is considered endangered in South Africa in view of its small breeding population and the threats to eggs and chicks. Earlier works based on capture-recapture data suggest that this population adopts a partial migratory strategy. Updated capture-recapture data were combined with new data on moult and stable isotopes of scapular feathers to determine whether subpopulations could be identified in the South African breeding population. Moult data on 404 individuals failed to identify subpopulations, but two groups were identifiable with the stable isotopes: one group of four individuals exhibiting low carbon and nitrogen stable isotope ratios and a second group (comprising the remaining 152 individuals) with significantly higher ratios. The isotope data suggest that birds from the two groups moulted in different areas. Comparisons with published studies showed that the 152 individuals had likely moulted their scapulars in South African waters, but the moulting area for the remaining four individuals could not be ascertained due to the absence of detailed isoscapes in the southern part of the Mozambique Channel. Further work investigating the genetic differentiation between South African and Madagascan Roseate Terns may bring new insight into the migratory behaviour of the South African population. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Five to seven subspecies of Antarctic Tern (Sterna vittata) are recognised, with at least three (S. v. vittata, S. v. tristanensis and S. v. sanctipauli) wintering in South Africa. Morphological characters used to define these subspecies are not perfectly reliable, but fidelity to nesting site suggests they could be genetically distinct. We used morphological data and DNA to investigate the validity of subspecies. We further used stable isotope analysis of feather samples collected from the non-breeding grounds in South Africa to attempt to ascertain the population of origin. Nuclear and mitochondrial DNA sequence data identified two major genetic clades: one mostly comprised individuals partially or completely matching the morphological description of S. v. tristanensis, the other included individuals from S. v. vittata and S. v. sanctipauli. Stable isotope values indicated that juveniles originated from at least three populations. Irrespective of their morphological and genetic characteristics, most immatures moulted in Antarctic waters, and adults moulted in various habitats. Their colony of origin could not therefore be inferred from stable isotope values from feathers. Results indicate that morphological groupings may reflect a north-south cline across the Indian Ocean. Adequate conservation strategies require rigorous reassessment of the currently accepted subspecies, including DNA analyses of samples from the breeding grounds, particularly on Amsterdam and St Paul Islands. [ABSTRACT FROM AUTHOR]

The Eastern Cape population of the Damara TernSternula balaenarumwas estimated to be 25–29 pairs in the 2008/09 and 2009/10 breeding seasons. The population appears to be stable and has probably increased slightly since the early 1990s. An eastward shift of the majority of nest sites in the Alexandria dunefields of 5–10 km was recorded since the early 1990s. Breeding Damara Terns caught at night and colour-flagged in the Alexandria dunefields averaged 12% heavier than the average mass of birds handled in Namibia and egg masses ranged from 11% to 22% heavier than 21 fresh egg masses recorded in Namibia. Adult Damara Terns caught at night while incubating, were ringed and marked with coloured leg-flags. All chicks located were also ringed and leg-flagged. A stable isotope analysis of scapular feathers suggested that breeding adults from the Eastern Cape may moult in similar areas to the Namibian population, i.e. West Africa. Small numbers of Damara Terns were recorded during the winter in the Eastern Cape. Although these included no colour-flagged birds, the numbers of birds marked were probably too low to draw any definite conclusions regarding the origin of over-wintering Damara Terns. [ABSTRACT FROM PUBLISHER]

The Cape gannet, Morus capensis, has long been considered a monomorphic species despite attempts at phenotypically separating the sexes. In a further effort we here recorded morphometric measurements from genetically sexed Cape gannets. Discriminant function analysis was used to classify sexes according to these morphometric measurements. Culmen and gular stripe lengths were selected as the best discriminators, correctly classifying 65% of birds. Male Cape gannets had significantly longer culmens and gular stripes than females. We thereby provide the first evidence suggesting that the Cape gannet demonstrates some level of dimorphism. Nonetheless, morphometric criteria used to separate sexes holds limited value due to overlap in measurements between sexes. [ABSTRACT FROM AUTHOR]

In-air sounds of pinnipeds are important for interactions with conspecifics and threat displays. However, little is known about the in-air acoustic repertoire and associated behaviour of crabeater seals Lobodon carcinophaga. We investigated the in-air acoustic repertoire and associated behaviour of two male and one female wild juvenile crabeater seals that beached separately, and were rehabilitated in Durban and Gqeberha, South Africa. In-air sounds were visually identified and categorised into five classes validated via random forest model classification: brief, intermediate, and long moan calls, croaks, and hisses. Hisses were common (n = 25,105 sounds from 136 hrs of acoustic recordings) and detected during heightened arousal states and interactions with animal care staff and a conspecific. Furthermore, hisses were also recorded in low arousal states during exhalation. Moan calls (n = 241) were only detected from two of the three seals. During rehabilitation, the female seal ceased producing moan calls and later produced a series of croaks (n = 204). Acoustic characteristics of in-air moan calls differed from published underwater moan calls according to duration, minimum, and maximum frequencies, and pulse repetition rate. Our study shows that the in-air acoustic repertoire and associated behaviour of these Antarctic seals are dynamic, vary inter-individually and are context dependent. [ABSTRACT FROM AUTHOR]