Sex allocation and sex‐specific parental investment in an endangered seabird

Abstract

Biased offspring sex ratio is relatively rare in birds and sex allocation can vary with environmental conditions, with the larger and more costly sex, which can be either the male or female depending on species, favoured during high food availability. Sex‐specific parental investment may lead to biased mortality and, coupled with unequal production of one sex, may result in biased adult sex ratio, with potential grave consequences on population stability. The African Penguin Spheniscus demersus, endemic to southern Africa, is an endangered monogamous seabird with bi‐parental care. Female adult African Penguins are smaller, have a higher foraging effort when breeding and higher mortality compared with adult males. In 2015, a year in which environmental conditions were favourable for breeding, African Penguin chick production on Bird Island, Algoa Bay, South Africa, was skewed towards males (1.5 males to 1 female). Males also had higher growth rates and fledging mass than females, with potentially higher post‐fledging survival. Female, but not male, parents had higher foraging effort and lower body condition with increasing number of male chicks in their brood, thereby revealing flexibility in their parental strategy, but also the costs of their investment in their current brood. The combination of male‐biased chick production and higher female mortality, possibly at the juvenile stage as a result of lower parental investment in female chicks, and/or at the adult stage as a result of higher parental investment, may contribute to a biased adult sex ratio (ASR) in this species. While further research during years of contrasting food availability is needed to confirm this trend, populations with male‐skewed ASRs have higher extinction risks and conservation strategies aiming to benefit female African Penguin might need to be developed.

Sex‐biased survival contributes to population decline in a long‐lived seabird, the Magellanic Penguin

“…), Southern Rockhopper Penguins (Morrison et al. ), and African Penguins (Spelt and Pichegru ). Regardless, sex is often ignored in contemporary research on penguin demographic rates (e.g., Sherley et al.…”

“…]; Adélie Penguins [Jennings et al. ]; African Penguin [Spelt and Pichegru ]). Because of their smaller size and less favorable surface area to volume ratio, female Magellanic Penguins may fledge at an energetic disadvantage to males, lowering their juvenile survival rates.…”

“…]; Southern Rockhopper Penguin, Eudyptes chrysocome [Morrison et al. ]; African Penguin, Spheniscus demersus [Spelt and Pichegru ]), the sex ratio of Magellanic Penguins at Punta Tombo is male biased (Boersma et al. ).…”

“…In most cases, the driver of biased ASR in penguin populations has not been formally tested, that is, using population matrix model perturbation analysis. Examples of biased hatching sex ratios (African Penguin; Spelt and Pichegru ) and of survival bias in juveniles (Southern Rockhopper Penguin; Dehnhard et al. ) and in breeding‐aged individuals (Yellow‐eyed Penguin [Richdale ]; Adélie Penguin [Ainley and DeMaster ]; King Penguin [Olsson and Van der Jeugd ]) have all been documented in penguins.…”

Does it always pay to defend one's nest? A case study in African penguin

“…In this study, we explored (i) whether boldness and mobility in nest defence (both associated with risk‐taking, Réale et al., ) may be consistent in African penguins and could, potentially, be assimilated to personality traits in that species; (ii) if individual nest defence behaviour and pair assortment by behaviour may influence breeding success; and (iii) if this relation may vary with food conditions. We hypothesized that males would be risk‐prone (bolder and more mobile) than females when defending their nests because of a potential biased sex ratio towards males in that population (Pichegru & Parsons, ; Spelt & Pichegru, ). Males will, therefore, ensure the keeping of a territory (Sundström, Petersson, Höjesjö, Johnsson, & Järvi, ) to maximize their chance to reproduce.…”