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

Abstract

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.

Age‐specific survival and movement among major African Penguin Spheniscus demersus colonies

“…, Sherley et al . ). This may also explain the unexpectedly low movement from Robben and Dassen islands to EWC after 2003 (but see immature movement from Dassen, Fig.…”

Video monitoring reveals novel threat to Critically Endangered captive-bred and released Regent Honeyeaters

“…Reproduction is a key vital rate determining the demographics of populations. There are numerous external influences that can reduce nest success in birds (here defined as the proportion of nests that fledge at least one young), including extreme weather (Jovani & Tella 2016), limited resources (Sherley et al 2014), competition (Frei et al 2015), brood parasitism (Wei et al 2015), parasites (Scott-Baumann and Morgan 2015) and anthropogenic habitat disturbance (Ibáñez-Álamo et al 2015). However, perhaps the most important driver of nest failure is predation (Ricklefs,1969;Major et al 2014).…”

Implications of spring water levels on the production of American white pelicans nesting at marsh lake, Minnesota

“…The availability of nesting habitat on preferred sites may be limiting the population at Marsh Lake. The number of nests on the low‐elevation sites away from the mainland (Eight‐acre and Big islands) is positively related to area available (i.e., area of the island above water), a pattern observed in other colonial nesting bird populations in which there are density‐dependent dynamics affecting reproduction (Sherley et al ). At Marsh Lake, nest density on Eight‐acre and Big islands was not related to area available (Fig.…”