Maëlle Connan

Drivers of Time-Activity Budget Variability during Breeding in a Pelagic Seabird

During breeding, animal behaviour is particularly sensitive to environmental and food resource availability. Additionally, factors such as sex, body condition, and offspring developmental stage can influence behaviour. Amongst seabirds, behaviour is generally predictably affected by local foraging conditions and has therefore been suggested as a potentially useful proxy to indicate prey state. However, besides prey availability and distribution, a range of other variables also influence seabird behavior, and these need to be accounted for to increase the signal-to-noise ratio when assessing specific characteristics of the environment based on behavioural attributes. The aim of this study was to use continuous, fine-scale time-activity budget data from a pelagic seabird (Cape gannet, Morus capensis) to determine the influence of intrinsic (sex and body condition) and extrinsic (offspring and time) variables on parent behaviour during breeding. Foraging trip duration and chick provisioning rates were clearly sex-specific and associated with chick developmental stage. Females made fewer, longer foraging trips and spent less time at the nest during chick provisioning. These sex-specific differences became increasingly apparent with chick development. Additionally, parents in better body condition spent longer periods at their nests and those which returned later in the day had longer overall nest attendance bouts. Using recent technological advances, this study provides new insights into the foraging behaviour of breeding seabirds, particularly during the post-guarding phase. The biparental strategy of chick provisioning revealed in this study appears to be an example where the costs of egg development to the female are balanced by paternal-dominated chick provisioning particularly as the chick nears fledging.

Sex Differentiation Based on the Gular Stripe in the Apparently Monomorphic Cape Gannet

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.

Reappraisal of the Trophic Ecology of One of the World's Most Threatened Spheniscids, the African Penguin.

Many species of seabirds, including the only penguin species breeding on the African continent, are threatened with extinction. The world population of the endangered African penguin Spheniscus demersus has decreased from more than 1.5 million individuals in the early 1900s to c.a. 23 000 pairs in 2013. Determining the trophic interactions of species, especially those of conservation concern, is important when declining numbers are thought to be driven by food limitation. By and large, African penguin dietary studies have relied on the identification of prey remains from stomach contents. Despite all the advantages of this method, it has well known biases. We therefore assessed the African penguin’s diet, using stable isotopes, at two colonies in Algoa Bay (south-east coast of South Africa). These represent over 50% of the world population. Various samples (blood, feathers, egg membranes) were collected for carbon and nitrogen stable isotope analyses. Results indicate that the trophic ecology of African penguins is influenced by colony, season and age class, but not adult sex. Isotopic niches identified by standard Bayesian ellipse areas and convex hulls, highlighted differences among groups and variability among individual penguins. Using Bayesian mixing models it was for the first time shown that adults target chokka squid Loligo reynaudii for self-provisioning during particular stages of their annual cycle, while concurrently feeding their chicks primarily with small pelagic fish. This has important ramifications and means that not only pelagic fish, but also squid stocks, need to be carefully managed in order to allow population recovery of African penguin.

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.

Dietary studies in birds: testing a non-invasive method using digital photography in seabirds

Summary 1.Dietary studies give vital insights into foraging behaviour, with implications for understanding changing environmental conditions and the anthropogenic impacts on natural resources. Traditional diet sampling methods may be invasive or subject to biases, so developing non-invasive and unbiased methods applicable to a diversity of species is essential. 2.We used digital photography to investigate the diet fed to chicks of a prey-carrying seabird, and compared our approach (photo-sampling) to a traditional method (regurgitations) for the greater crested tern Thalasseus bergii. 3.Over three breeding seasons, we identified >24,000 prey items of at least 48 different species, more than doubling the known diversity of prey taken by this population of terns. We present a method to estimate the length of the main prey species (anchovy Engraulis encrasicolus) from photographs, with an accuracy < 1 mm and precision ~0.5 mm. Compared to regurgitations at two colonies, photo-sampling produced similar estimates of prey composition and size, at a faster species accumulation rate. The prey compositions collected by two researchers photo-sampling concurrently were also similar. 4.Photo-sampling offers a non-invasive tool to accurately and efficiently investigate the diet composition and prey size of prey-carrying birds. It reduces biases associated with observer-based studies and is simple to use. This methodology provides a novel tool to aid conservation and management decision-making in light of the growing need to assess environmental and anthropogenic change in natural ecosystems. This article is protected by copyright. All rights reserved.

Trophic investigations of Cape fur seals at the easternmost extreme of their distribution

The diet of Cape fur seals Arctocephalus pusillus pusillus in the eastern portion of their distribution has received little attention previously, and was studied using traditional methods only. In 2013 we therefore assessed the diet of seals at the easternmost colony at Black Rocks, Algoa Bay, South Africa (33°50′ S, 26°16′ E) from both scats and the analysis of stable isotopes in blood, guard hairs and whiskers. Information from both sources indicated that seals at this site are generalist predators feeding on a mix of pelagic (mainly anchovy Engraulis encrasicolus and chokka squid Loligo reynaudii) and benthic species (tonguefish Cynoglossus spp., East Coast sole Austroglossus capensis and horsefish Congiopodus spp.). Stable isotope analysis revealed that the diet of individual females may differ consistently as a result of different individual foraging preferences or strategies. There were no differences in the diet between summer and winter. Furthermore, our results suggest that stable isotopes in three-month-old pups can be used as proxies for the diet of lactating females, using female-to-pup discrimination factors presented here. Future research should consider an extension of this approach to fully resolve ecological partitioning between individual Cape fur seals to better understand their role in ecosystem dynamics.

Morphological versus molecular identification of Sooty (Phoebetria fusca) and Light-mantled (P. palpebrata) albatross chicks

The two fuliginous albatross species, Phoebetria fusca (the Sooty albatross, SA) and P. palpebrata (the Light-mantled albatross, LMA), are found breeding close to each other on the Prince Edward Islands (Southern Ocean). Adults of these two species are easy to identify in the field, but the chicks are difficult to distinguish on the basis of external morphology, especially at very young ages. Many ecological studies involve sampling of chicks as well as adults, and accurate field identification of chicks is thus crucial. Traditionally, the extent of the ring of pale feathers around the eye (eye-ring) has been used to identify the fledglings. The aim of our study was to investigate the utility of characters associated with the eye-ring (extent, measured as an angle, and colour) for the identification of Phoebetria chicks. This was achieved by comparison of identifications based on morphology, with positive identifications based on DNA sequence data from the mitochondrial cytochrome b gene. We confirm the value of morphological criteria in distinguishing LMA and SA chicks, and this technique appears to be accurate in the majority of cases (>80%). However, we recommend using molecular identification for borderline cases (angle of the eye-ring measuring between 85 and 95°) if independent confirmation of chick identity cannot be obtained (e.g. via observed feeding interaction with an adult).

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.

The subspecies of Antarctic Terns (Sterna vittata) wintering on the South African coast: evidence from morphology, genetics and stable isotopes

Abstract 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.

Ontogeny, tissue, and species but not sex influence stable isotopic values of three albatross species

The use of indirect dietary markers, including stable isotopes, has immensely improved our knowledge of seabird trophic ecology throughout their annual cycle. Important aspects include differences in trophic niche between adults and chicks at the intra- and inter-specific levels and tissue-dependent differentiation in chicks. Using stable isotopic niche as a proxy for trophic ecology, we investigated how three closely related albatross species co-exist in the sub-Antarctic Prince Edward Islands. The effects of age, sex, tissue, and species on the isotopic niche were observed for Grey-headed Thalassarche chrysostoma, Sooty Phoebetria fusca, and Light-mantled Phoebetria palpebrata Albatrosses breeding on Marion Island. At the end of chick-rearing, carbon and nitrogen stable isotope values differed according to age, tissue, and species but not the sex of either adults or chicks. A complex pattern was revealed as the three species exhibited contrasting results. For example, values for δ13C or δ15N of chick blood could be depleted, enriched or similar relative to that of adults, depending on species. Stable isotope differences between blood and feathers likely reflect differences in their amino acid composition, while adult/chick differences will relate to their different physiological needs and diet. The results indicate that co-existence of the three species on the island is facilitated through resource partitioning among species in terms of foraging areas and in the trophic levels at which adults feed for themselves and their chicks. This work brings new insights into the effect of intrinsic factors on the foraging ecology of marine top predators.