Two is too many: does being a single parent reduce the risk of nest predation?
Julien Bouvet  1@  , Agnès Hivet  2  , Olivier Gilg  3  , Loïc Bollache  3  , Jérôme Moreau  4  , François-Xavier Dechaume-Moncharmont  5  
1 : Laboratoire d'Ecologie des Hydrosystèmes Naturels et Anthropisés (UMR 5023)
Université Claude Bernard Lyon 1, Ecole Nationale des Travaux Publics de l'Etat, Centre National de la Recherche Scientifique
2 : Département de Biologie
Université Claude Bernard et ENS Lyon
3 : Laboratoire Chrono-environnement (UMR 6249)
Centre National de la Recherche Scientifique, Université de Franche-Comté
4 : Biogéosciences [UMR 6282]
Université de Bourgogne, Centre National de la Recherche Scientifique
5 : Laboratoire d'Ecologie des Hydrosystèmes Naturels et Anthropisés (UMR 5023)
Université Claude Bernard Lyon 1, Ecole Nationale des Travaux Publics de l'Etat, Centre National de la Recherche Scientifique

Offspring predation is one of the main drivers of reproductive failure in species reproducing in nest, burrow or den. This selective pressure promotes the evolution of passive defence strategies based on nest concealment or limited activity at nest. A frequently cited verbal model proposed by Alexander Skutch (1949) predicts that parental activity at nest should decrease as a response to an increasing predation risk. This has then been repeatedly invoked to explain the evolution of uniparental care strategy. The rationale is that a nest of biparental species is more conspicuous than the one of a uniparental species because regular change-over between the parents induce more activity (successive take-off and arrival, vocal display during nest relief). The biparental nest would thus be more easily spotted by predators. Surprisingly, this verbal model has never been rigorously tested. Our aim was to assess the idea that predation pressure can favour the evolution of uniparental strategy over the biparental one. In a wide range of parameters, despite higher instantaneous risk of nest detection, biparental care strategy is a sensible strategy to mitigate predation risk because it allows for longer recess and less frequent movement at nest. Even extraordinarily conspicuous nest activity in the biparental strategy is not sufficient to explain the evolution of the uniparental strategy. We have also calibrated the model's parameter (frequency of nest departure, arrival and change-over) on eight shorebird species from a genus of Arctic ground nesting birds known for their diversity of parental care strategies. All uniparental species were predicted to be biparental under the sole assumption of nest conspicuousness. This result illustrates that the predation risk alone is not a sufficient driver for the evolution of uniparental care strategy in these species. More generally, without completely dismissing this hypothesis in some ecological contexts, we advocate greater caution when invoking the Skutch hypothesis to justify the evolution of uniparental over biparental care.


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