Avian Egg Timers: Female Cowbirds Judge Past, Present, and Future When Making Nest Parasitism Decisions

David J White

doi:10.3389/fevo.2020.00203

Abstract

The cognitive demands associated with brood parasitism are substantial. Not only must female parasites locate nests and assess their suitability for parasitism, they must also time parasitism to correspond with the breeding behavior of the host. Keeping track of the reproductive state of hosts for a variety of nests allows the parasite to select a nest where their egg can be incubated successfully. Thus, nest selection decisions are integral to obligate brood parasites’ reproductive success. In captive breeding flocks of brown-headed cowbirds (Molothrus ater), I studied (1) females’ abilities to time a host nest’s readiness for parasitism and (2) the timing of females’ nest selection decisions. I found that cowbirds can attend to the amount of time that elapsed since a host egg was added to a nest and can use that information to choose a nest for parasitism. Females made their choice of nest during prospecting the day before they laid, and, once decided, they did not update their decisions on the day of laying. Taken together, the results reveal that female cowbirds process substantial amounts of information about location, time, number, and rate in order to plan for future parasitism. This research program reveals that species-typical decisions integrate a variety of general and specialized cognitive abilities to allow females to behave adaptively and maximize reproductive success.

Highlights

Understanding the animal mind has been of keen interest to researchers and laypeople for centuries (Dewsbury, 1989; Shettleworth, 2010)
Due to renewed interest from both biologists and psychologists working in the lab and field, and integrating function with the underlying mechanisms controlling decision processes, advances are being made in our understanding of animal cognition at a pace unmatched in the past (Bouton, 2007; Pearce, 2008)
Experiment 2 reveals compelling evidence that females are assessing nests and deciding on the nest best suited for parasitism during the prospecting day prior to egg laying

Summary

Introduction

Understanding the animal mind has been of keen interest to researchers and laypeople for centuries (Dewsbury, 1989; Shettleworth, 2010). Research into how animals acquire, process and act on information has come in fits and starts across this time; there have been decades of tremendous interest and others of complete disregard. Functional perspectives into cognition consider the information processing skills that animals possess to be specialized adaptations, evolved to deal with species-specific ecological demands (Sherry and Schacter, 1987). One of the critical implications of this perspective is that cognitive performance in real-world tasks is under selection pressure, and heritable variation in cognitive performance must relate in some manner to fitness. Work under this perspective is often done examining species-typical behavior in the animals’ natural habitat. While the connection between cognition and fitness is only starting to be discovered in some animal systems (see Sol et al, 2005; Cole et al, 2012; Cauchard et al, 2017; and other articles in this special issue) the evolutionary perspective provides a powerful organizing perspective

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