Rockhopper Penguin–Imperial Cormorant mixed colonies in the Falkland Islands: a stroke of luck for late breeders

Virginia Morandini,Katie M Dugger,Miguel Ferrer,David Ainley

doi:10.1002/ecs2.3272

Virginia Morandini, Katie M Dugger + Show 2 more

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https://doi.org/10.1002/ecs2.3272

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Abstract

AbstractMixed‐species colonies occur frequently, especially among seabirds, and may provide mutual benefits among associated species including antipredator advantages. The “protector” species in such associations may provide early warning signals or by aggressively defending their own nests, may expel predators from the area. We explored costs and benefits to Rockhopper Penguins (Eudyptes chrysocome) in relation to offspring production in both monospecific colonies and those mixed with Imperial Cormorants (Phalacrocorax atriceps) at Saunders Island (Falkland Islands), emphasizing differences in predation pressure. We considered behavioral responses of chicks (in crèches), as well as differences in their nutritional condition, morphometric measurements, and survival compared among different breeding colonies. Our study revealed a paradox: High‐quality adult penguins, those arriving early and occupying lower‐elevation sites closer to the coast, produced better‐nourished chicks earlier in the season. However, they averaged half the number of chicks fledged, compared to breeders that arrived later in the season. Late breeders were forced by unavailability of optimal habitat to nest in more elevated areas, forming mixed colonies with cormorants, which, in turn, provided them with protection from nest predators. This study provides an example of the role of luck in nature, and how it may compensate for differences in individual fitness.

Highlights

The most commonly proposed hypotheses for the evolution of colonial breeding in birds focus on advantages related to reducing nest predation and enhancing resource acquisition (Lack 1968, Hoogland and Sherman 1976)
(3) for penguin productivity, we investigated the association between predation pressure and the proportion of breeding cormorants
Predators/ Rockhopper chicks the sea (Fig. 1). These nesting patterns confounded our ability to clearly differentiate between colony positions vs. the effect of the proportion of breeding cormorants on penguin productivity at these colonies

Summary

Introduction

The most commonly proposed hypotheses for the evolution of colonial breeding in birds focus on advantages related to reducing nest predation and enhancing resource acquisition (Lack 1968, Hoogland and Sherman 1976). Predator swamping occurs when predators can eat only a small proportion of the available prey Colonial birds may breed synchronously so that most chicks are present at the same time and place to thereby overcome the predator’s ability to prey on every chick. Even if breeding colonies attract predators (Brown 1967), this swamping effect, together with the collective antipredator behavior of colony members, such as early warning calls, mobbing, and attacks, leads to a decrease in net predation rates.

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