Richard B. Sherley

Artificial nests enhance the breeding productivity of African Penguins (Spheniscus demersus) on Robben Island, South Africa

Abstract Loss of nesting habitat threatens many cavity nesting birds worldwide and has contributed to the decline of several species of burrow-nesting seabirds. Replacing lost habitat with artificial nesting structures is considered to be a useful conservation intervention. Here we report on an investigation into the effectiveness of such a strategy—providing artificial nests for the endangered African Penguin (Spheniscus demersus) at a colony on Robben Island, South Africa. The re-colonisation of Robben Island by breeding African Penguins in the 1980s was partly attributed to the availability of shaded nesting habitat under introduced vegetation. However, the suitability of this habitat had not been tested empirically. In addition, artificial nests have been present at Robben Island since 2001, but whether they were a viable means of providing improved nesting habitat was not known. The reproductive output of African Penguins was monitored on Robben Island from 2001 to 2010. Breeding success varied between years but, overall, was within the range of figures previously reported for the species. Relative to pairs in nests under vegetation, birds occupying artificial nests and nests in abandoned buildings had increased nesting survival during chick-rearing, with 9 and 13% more chicks fledged per egg hatched over the study period. These artificial structures seem to offer the advantages of shelter from the weather and protection from predators, without the risks of collapse associated with natural burrows in non-guano substrates. This study supports findings from Namibia, and also supports the continued use of artificial nests as a conservation tool throughout the range of the species.

Bottom-up effects of a no-take zone on endangered penguin demographics

Marine no-take zones can have positive impacts for target species and are increasingly important management tools. However, whether they indirectly benefit higher order predators remains unclear. The endangered African penguin (Spheniscus demersus) depends on commercially exploited forage fish. We examined how chick survival responded to an experimental 3-year fishery closure around Robben Island, South Africa, controlling for variation in prey biomass and fishery catches. Chick survival increased by 18% when the closure was initiated, which alone led to a predicted 27% higher population compared with continued fishing. However, the modelled population continued to decline, probably because of high adult mortality linked to poor prey availability over larger spatial scales. Our results illustrate that small no-take zones can have bottom-up benefits for highly mobile marine predators, but are only one component of holistic, ecosystem-based management regimes.

Storms and heat limit the nest success of Bank Cormorants: implications of future climate change for a surface-nesting seabird in southern Africa

AbstractThe Bank Cormorant Phalacrocorax neglectus is endemic to the Benguela Upwelling System of southern Africa. Most breeding colonies occur on offshore rocks, islands or man-made structures close to the high-water mark. Despite adaptations for breeding close to the water, nests can be lost to storms. Using data from two colonies where food is not considered limiting, we present a comparative study on nest survival in Bank Cormorants. Using a combination of the Mayfield method and parametric survival analysis, nest success was compared in nests on man-made structures at Robben Island, South Africa, where birds breed during the austral winter, with nests on man-made and natural structures at Mercury Island, Namibia, where Bank Cormorants breed during the austral summer. Overall, the probability of a nest surviving the breeding attempt was lower at Robben Island than at Mercury Island in all three seasons. Nest failures at Robben Island were related to wave heights and air temperature, with trends to suggest reduced chick survival in years where major storm events occurred during peak breeding. A heat wave appeared to cause major chick mortality at Mercury Island in 2005. Nest survival was relatively invariable between years at the main site monitored on Mercury Island, where nests were partially sheltered from the sun, but breeding productivity was poor in comparison to other cormorant species. Winter breeding in South Africa may increase the risk from storms but reduce the risk of heat exposure. An understanding of the impact of stochastic events on Bank Cormorants may be important in safe-guarding the continued survival of the species, particularly in light of the risks posed by future climate change.ZusammenfassungStürme und Hitze limitieren den Bruterfolg der KüstenscharbePhalacrocorax neglectus: Auswirkungen des Klimawandels auf einen nahe des Meeresspiegels brütenden Seevogel im südlichen Afrika Die Küstenscharbe Phalacrocorax neglectus ist endemisch für das Auftriebsgebiet des Benguela-Stroms im südlichen Afrika. Die meisten Brutkolonien befinden sich auf Felsen, Inseln und künstlichen Strukturen kurz über der Hochwassermarke. Trotz Anpassungen an das Brüten nahe der Wasserlinie werden Nester oft durch Stürme zerstört. In dieser Studie vergleichen wir den Bruterfolg der Küstenscharbe in zwei unterschiedlichen Kolonien, in denen keine Nahrungsknappheit vorliegt. Mit Hilfe der Mayfield-Methode und parametrischer Tests zur Berechnung der Überlebensrate wurden der Bruterfolg von Tieren auf Robben Island, Südafrika, und Mercury Island, Namibia verglichen. Auf Robben Island brüten die Tiere im dortigen Winter auf künstlichen Strukturen, während die Vögel auf Mercury Island während der Sommermonate sowohl auf natürlichen als auch auf künstlichen Strukturen brüten. In allen drei Untersuchungsjahren lag der Bruterfolg auf Robben Island unter dem von Mercury Island. Nestverluste auf Robben Island wiesen einen Zusammenhang mit Wellenhöhe und Lufttemperaturen auf und höhere Kükenverlusten wurden in Jahren beobachtet, in denen große Sturmereignisse mit der Hauptbrutperiode zusammenfielen. Eine Hitzewelle in 2005 verursachte ein großes Kükensterben auf Mercury Island. Der Bruterfolg schwankte nur gering auf Mercury Island in der Hauptbrutkolonie, wo Nester teilweise geschützt und im Schatten lagen. Im Vergleich zu anderen Kormoranarten war der Bruterfolg aber eher gering. Das Brüten im Winter bei Tieren in Südafrika verringert die Gefahr der Verluste durch Hitzwellen, erhöht aber die Gefahr von Nestverlusten durch Stürme. Ein besseres Verständnis der Einflüsse von stochastischen Wetterereignissen auf den Bruterfolg dieser bedrohten Art ist besonders wichtig in Hinblick auf den Klimawandel und damit einhergehenden Veränderungen im Wetter.

Interactions between snakes and seabirds on Robben, Schaapen and Meeuw Islands, Western Cape province, South Africa

(2009). Interactions between snakes and seabirds on Robben, Schaapen and Meeuw Islands, Western Cape province, South Africa. Ostrich: Vol. 80, No. 2, pp. 115-118.

Hand-Rearing, Release and Survival of African Penguin Chicks Abandoned Before Independence by Moulting Parents

The African penguin Spheniscus demersus has an ‘Endangered’ conservation status and a decreasing population. Following abandonment, 841 African penguin chicks in 2006 and 481 in 2007 were admitted to SANCCOB (Southern African Foundation for the Conservation of Coastal Birds) for hand-rearing from colonies in the Western Cape, South Africa, after large numbers of breeding adults commenced moult with chicks still in the nest. Of those admitted, 91% and 73% respectively were released into the wild. There were veterinary concerns about avian malaria, airsacculitis and pneumonia, feather-loss and pododermatitis (bumblefoot). Post-release juvenile (0.32, s.e.  = 0.08) and adult (0.76, s.e.  = 0.10) survival rates were similar to African penguin chicks reared after oil spills and to recent survival rates recorded for naturally-reared birds. By December 2012, 12 birds had bred, six at their colony of origin, and the apparent recruitment rate was 0.11 (s.e.  = 0.03). Hand-rearing of abandoned penguin chicks is recommended as a conservation tool to limit mortality and to bolster the population at specific colonies. The feasibility of conservation translocations for the creation of new colonies for this species using hand-reared chicks warrants investigation. Any such programme would be predicated on adequate disease surveillance programmes established to minimise the risk of disease introduction to wild birds.

Processes influencing the population dynamics and conservation of African penguins on Dyer Island, South Africa

Dyer Island, South Africa, supported the largest African penguin Spheniscus demersus colony in 1979 (22 655 breeding pairs), but population dynamics of the species have not followed the trends of adjacent colonies in years of high fish abundance or shifts in prey distribution. Less than 1 500 pairs were breeding on Dyer Island in 2013. Available knowledge on demographic parameters was collated and ecological processes were quantified. Juvenile and adult survival probabilities estimated for birds ringed on Dyer Island between 2005 and 2011 were 0.247 (SE 0.06) and 0.545 (SE 0.05) respectively. Juveniles had a high probability (0.918; SE 0.077) of moving away from Dyer Island. Predation by seals and kelp gulls, as well as oiling, are currently important top-down pressures on penguins on Dyer Island. Numbers of birds breeding on the island were negatively correlated with purse-seine catches 20 nautical miles around it. However, it seems that once the colony size is <3 500 breeding pairs, the importance of fishing pressure diminishes, suggesting that once a colony has been reduced to a relatively small size, its growth is limited by pressures other than fishing. From the review of available knowledge presented here, we recommend a number of management options that should be tested in a suitable model.

Ostrich chick humoral immune responses and growth rate are predicted by parental immune responses and paternal colouration

One of the most important measures of offspring performance is growth rate, which is often traded off against another important survival trait, immune function. A particular feature of ostrich chicks maintained in farmed environments is that cohorts of chicks vary widely in size. As parents can have a profound effect on the phenotype and fitness of their offspring, we investigated whether chick growth and immune defence were related to variation in levels of immune defence in their genetic parents. As secondary sexual traits of sires could serve as indicators of male quality, and be used in female mating decisions, we also investigated whether chick growth rate and immune defence were related to male plumage and integumentary colouration. We found that offspring growth rates and humoral responses were related to the humoral responses of their parents, suggesting that at least some components of humoral immune capacity are heritable. The white colour of male ostrich feathers was correlated to the humoral response and growth rate of their offspring, suggesting that this visual cue involved in the male courtship display could serve as an important signal to females of male quality, thereby forming the basis of mate choice in this species.

Growth and decline of a penguin colony and the influence on nesting density and reproductive success

Colonial breeding is characteristic of seabirds but nesting at high density has both advantages and disadvantages and may reduce survival and fecundity. African penguins (Spheniscus demersus) initiated breeding at Robben Island, South Africa in 1983. The breeding population on the island increased in the late 1990s and early 2000s before decreasing rapidly until 2010. Before the number breeding peaked, local nest density in the areas where the colony was initiated plateaued, suggesting that preferred nests sites were mostly occupied, and the area used by breeding birds expanded. However, it did not contract again as the population decreased, so that nesting density varied substantially. Breeding success was related positively to the prey available to the breeding birds and negatively to local nest density, particularly during the chick-rearing period, suggesting a density-dependence operating through social interactions in the colony, possibly exacerbated by poor prey availability when the breeding population was large. Although nest density at Robben Island was not high, nesting burrows, which probably reduce the incidence of aggressive encounters in the colony, are scarce and our results suggest that habitat alteration has modified the strength of density-dependent relationships for African penguins. Gaining a better understanding of how density dependence affects fecundity and population growth rates in colonial breeders is important for informing conservation management of the African penguin and other threatened taxa.

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.

Defining ecologically relevant scales for spatial protection with long‐term data on an endangered seabird and local prey availability

Human activities are important drivers of marine ecosystem functioning. However, separating the synergistic effects of fishing and environmental variability on the prey base of nontarget predators is difficult, often because prey availability estimates on appropriate scales are lacking. Understanding how prey abundance at different spatial scales links to population change can help integrate the needs of nontarget predators into fisheries management by defining ecologically relevant areas for spatial protection. We investigated the local population response (number of breeders) of the Bank Cormorant (Phalacrocorax neglectus), a range-restricted endangered seabird, to the availability of its prey, the heavily fished west coast rock lobster (Jasus lalandii). Using Bayesian state-space modeled cormorant counts at 3 colonies, 22 years of fisheries-independent data on local lobster abundance, and generalized additive modeling, we determined the spatial scale pertinent to these relationships in areas with different lobster availability. Cormorant numbers responded positively to lobster availability in the regions with intermediate and high abundance but not where regime shifts and fishing pressure had depleted lobster stocks. The relationships were strongest when lobsters 20-30 km offshore of the colony were considered, a distance greater than the Bank Cormorants foraging range when breeding, and may have been influenced by prey availability for nonbreeding birds, prey switching, or prey ecology. Our results highlight the importance of considering the scale of ecological relationships in marine spatial planning and suggest that designing spatial protection around focal species can benefit marine predators across their full life cycle. We propose the precautionary implementation of small-scale marine protected areas, followed by robust assessment and adaptive-management, to confirm population-level benefits for the cormorants, their prey, and the wider ecosystem, without negative impacts on local fisheries.