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

Abstract

Reliable estimates of survival and dispersal are crucial to understanding population dynamics, but for seabirds, in which some individuals spend years away from land, mortality and emigration are often confounded. Multistate mark–recapture methods reduce bias by incorporating movement into the process of estimating survival. We used a multistate model to provide unbiased age‐specific survival and movement probabilities for the Endangered African Penguin Spheniscus demersus based on 5281 nestlings and 31 049 adults flipper‐banded and resighted in the Western Cape, South Africa, between 1994 and 2012. Adult survival was initially high (≥ 0.74) but declined after 2003–2004 coincident with a reduction in the availability of Sardine Sardinops sagax and Anchovy Engraulis encrasicolus on the west coast of South Africa. Juvenile survival was poorly estimated, but was lower and more variable than adult survival. Fidelity to the locality of origin varied over time, but was high in adults at Robben and Dassen islands (≥ 0.88) and above 0.55 for juvenile and immature Penguins at all localities. Movement occurred predominantly during 1994–2003 and was indicative of immigration to Robben and Dassen islands. Our results confirm that a prolonged period of adult mortality contributed to the observed decline in the African Penguin population and suggest a need for approaches operating over large spatial scales to ensure food security for marine top predators.

A changing distribution of seabirds in South Africa—the possible impact of climate and its consequences

“…Although Cape cormorants may move between breeding localities (Crawford et al, 1994), they also show fidelity to natal and nest sites (Berry, 1977;Hockey et al, 2005). Both African penguins and Cape cormorants have a restricted foraging range when breeding (e.g., Heath and Randall, 1989;Pichegru et al, 2010a;Hamann et al, 2012) and they suffered high adult mortality in the 1990s and 2000s in periods of prey scarcity off western South Africa (Crawford et al, 1992(Crawford et al, , 2011Waller and Underhill, 2007;Sherley et al, 2014). Cape gannets have a much greater foraging range during breeding (Lewis et al, 2006) and supplement their diet by feeding on offal discarded by fisheries when their natural prey is scarce, thereby buffering adult survival (e.g., Berruti et al, 1993;Pichegru et al, 2007;Grémillet et al, 2008;Distiller et al, 2012;Crawford et al, 2014b).…”

“…A better understanding of the mechanisms driving seabird populations in South Africa will result from development of integrated population models that account for movement between colonies (e.g., Sherley et al, 2014) and of models that account for multiple factors that may be influencing populations. The former are hampered to some extent by insufficient mark-recapture information properly to estimate survival and rates of migration between regions for some species and age classes of birds (e.g., Distiller et al, 2012).…”

“…Furthermore, it is frequently difficult to disentangle the influence of the environment from anthropogenic impacts, such as fishing (e.g., Coetzee et al, 2008). However, in the Benguela ecosystem several studies have demonstrated relationships between the abundance of prey and numbers of breeding seabirds or their demographic parameters, such as breeding success and survival (e.g., Crawford et al, 2006Crawford et al, , 2007Crawford et al, , 2011Crawford, 2007;Sabarros et al, 2012;Sherley et al, 2013Sherley et al, , 2014. Therefore, it may be expected that factors influencing the distribution of prey species, and hence its regional availability, will impact on seabirds.…”

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

“…MPAs can contribute towards the conservation of marine predators, but rarely protect highly mobile species throughout their life cycle [2,3,19]. African penguins feed far from colonies when not breeding and have suffered poor adult survival over the last decade as the regional abundance of sardine fell below a critical threshold [17,20]. It is becoming increasingly clear that fishing can exacerbate forage fish population collapses [11], with consequences for predators [21].…”

“…where N t is a vector holding the numbers in each stage at time t, and A is the population projection matrix: For A, f j ¼ first year survival (0.343) and f a ¼ immature and adult survival (0.743), as studies suggest they are equivalent [17]. Fecundity (F) ¼ P  f  R  f a , where P ¼ breeding probability (assumed to be 1); f ¼ proportion of females in the population (assumed to be 0.5) and R ¼ E  B  f e  f c , where E ¼ clutch size (1.86 eggs) [18], B ¼ breeding frequency (1.27 clutches per annum) [18], f e ¼ egg survival (0.548) [18] and …”