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

Fan

Bird Conservation International

et al. 2011

SummaryThe Chinese Crested Tern Thalasseus bernsteini is a Critically Endangered species and very little is known about its breeding biology and behaviour. Only two small breeding colonies have been recorded on the eastern coast of China. Between 2004 and 2009, their breeding biology was studied in two mixed species colonies on the Jiushan and Wuzhishan archipelagos in Zhejiang province. Chinese Crested Terns started breeding in late May and departed in late August, and nests were generally found within large colonies of Greater Crested Terns T. bergii. The nesting grounds of the mixed colony included grass, rock and interlaced zones on small, uninhabited islets. A total of six Chinese Crested Tern nests were identified, four of which were monitored. In these, the average clutch size was one, with an incubation period of 22–28 days and a fledging period of 31–35 days. The chicks subsequently joined chicks of the Greater Crested Tern, forming the same crèche. Adult Chinese Crested Terns foraged within approximately 5 km of the breeding islets and fed their chicks mainly with small and/or young shoaling fishes. The breeding success of Chinese Crested Tern was 100% in both 2008 and 2009. In addition to mixed nesting, other traits of breeding biology, such as breeding site shifts and re-nesting, provide valuable information for surveying, monitoring and conservation of the Chinese Crested Tern.

Section: Discussionmentioning

confidence: 66%

The breeding biology of Chinese Crested Terns in mixed species colonies in eastern China

Fan

Bird Conservation International

et al. 2011

“…African penguins also fight over nest sites (Eggleton and Siegfried 1979) and will attack chicks that wander from their nest (Seddon and van Heezik 1993). Their chicks are subject to predation by feral cats (Felis catus; Crawford et al 1995Crawford et al , 2011, kelp gulls (Larus dominicanus; Wilson 1985) and mole snakes (Pseudaspis cana; Underhill et al 2009) at Robben Island. Kelp gulls in particular are more active in high density areas in Magellanic penguin colonies (Stokes and Boersma 2000), although this effect may depend on the predatory species involved (Brunton 1999).…”

Section: Discussionmentioning

confidence: 99%

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

et al. 2013

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.

“…Based on our examination of dietary data from the literature, we estimated Levins' measure of niche breadth for the rhombic eggeater as B = 1.00 (based on 31 feeding records; Bates & Little, 2013), boomslang as B = 2.91 (based on 133 feeding records; Smith et al, 2019), cape cobra as B = 4.00 (based on 101 feeding records; Layloo, Smith & Maritz, 2017) and mole snake as B = 3.23 (based on Dyer, 1996;Underhill et al, 2009;and assorted feeding records from various literature and citizen science reports (Maritz & Maritz, 2020), see Table S6). We standardized these to B A = 0.00 (rhombic egg-eater), B A = 0.32 (boomslang), B A = 0.50 (cape cobra) and B A = 0.47 (mole snake), respectively (Fig.…”

Section: Relationship Between Dietary Niche and Head Morphologymentioning

confidence: 99%

Specialized morphology, not relatively large head size, facilitates competition between a small‐bodied specialist and large‐bodied generalist competitors

Barends

Maritz

2021

Journal of Zoology

Interspecific competition for limited resources should theoretically occur between species that are morphologically similar to each other. Consequently, species that reduce competition by adapting to specialize on a specific resource should be morphologically disparate to sympatric contemporaries and show evidence of phenotypic specialization. However, few studies have compared the morphologies of specialist and generalist competitors. In this context, we compare the feeding morphology and diet of an obligate, specialist, bird-egg-eating snake to three sympatric generalists that only facultatively consume bird eggs. We measured and compared body and head morphology of preserved museum specimens of each of four, syntopic snake species from southern Africa: the obligate bird-egg-eating rhombic egg-eater (Dasypeltis scabra), and the facultative bird-egg-eating boomslang (Dispholidus typus), cape cobra (Naja nivea) and mole snake (Pseudaspis cana). Given the physical challenges of consuming bird eggs in snakes, we predicted that consumption of bird eggs would be facilitated by the evolution of relatively larger heads in the smaller-bodied Dasypeltis. We found that head size was not phylogenetically conserved in the clades of these taxa and that contrary to our expectations, the specialist egg-eaters evolved to possess significantly smaller heads relative to body size than their competitors. We found a positive relationship between dietary niche breadth and head size within these species and their close relatives. Thus, relatively large-headed species have evolved diverse diets that overlap with the restricted diets of the small-headed specialist thereby producing this atypical competitive interaction. Our findings suggest that specialized adaptations can decouple typical body-size-constrained competition dynamics between sympatric snake species and highlight the complexity of the origins of dietary specialization.