Starlings

Starlings matter here not as a collection of observed habits alone, but as a test case for distinguishing population-wide restraint from reproductive decisions that benefit the individuals making them. Their great winter roosts could seem to measure abundance and limit breeding for the good of the group. The alternative developed in the book preserves a possible role for density cues while changing their evolutionary meaning: a female could use them to forecast competition for food, while an individual bird might also benefit by making the crowd seem larger than it is.

Winter Roosts and the Census Hypothesis

Wynne-Edwards proposed that large animal gatherings can serve as population censuses. In the starling example, birds mass at their evening roosts; on this account, such congregations let individuals estimate population density and adjust their birth rates when numbers are high. The argument links a visible collective spectacle to an automatic reproductive response, not to conscious arithmetic: sensory perception of crowd density might be connected through nervous or hormonal mechanisms to reproduction.

The book treats this proposal as plausible in outline but not established by the examples offered in its support. There is no direct evidence that animal aggregations actually function as epideictic displays, or population-estimation gatherings. The gathering itself therefore does not show that starlings assemble to restrain reproduction for a collective benefit. The same possible link between crowding and fertility can be approached through a different account of whose reproductive success is at stake.

Density as Information for Individual Breeding

On the selfish-gene account, a female’s reproductive success depends not simply on how many eggs she lays, but on how many offspring she can rear. An overcrowded population may foreshadow food scarcity. If a starling can estimate how dense its species is during winter, that information could help it predict how difficult it will be to feed chicks in the following spring and lower its clutch size accordingly.

This is presented as a logical possibility, not as a demonstrated fact about starlings. The chapter imagines a test in which birds exposed to recordings of a dense, loud winter roost lay fewer eggs than birds hearing a quieter, less crowded roost. Such a result would show that calls can provide information affecting reproduction; by the proposed definition, the calls would constitute an epideictic display. Yet that observation would not by itself establish group-benefit restraint. Females might respond to density because it helps them choose a clutch size that maximizes the number of young they themselves can rear.

The distinction is between a similar possible outcome and different evolutionary explanations. Both accounts can predict fewer eggs when a population is crowded. In the individual-centered version, genes that lead an animal to have a larger family than it can support are penalized because the offspring carrying them are less likely to survive to adulthood. Family planning consequently means optimizing birth rates, not limiting them for the public good. The starling example shows how evidence that appears to support group selection could, if found, still fit a selfish-gene explanation.

The Possibility of Misleading the Crowd

Density cues create a further complication. If a starling benefits by laying fewer eggs when it predicts strong competition, and makes that prediction from the volume of noise at the roost, another bird could gain by making the population sound larger than it is. The book proposes that an individual might call especially loudly, effectively making itself seem like more than one bird and inducing neighboring females to reduce their clutches below what conditions actually require.

This proposed tactic is named the Beau Geste Effect, after a novel in which a unit of the French Foreign Legion used a similar deception. In the starling case, its predicted advantage is reproductive: if other birds rear fewer young, fewer individuals carrying rival genes will be produced, while the deceiver’s own genes may benefit. The possibility reverses the apparent meaning of a shared census. What might look like a collective mechanism for regulating population size could also invite manipulation by individuals whose interests are not identical to those of their neighbors.

The account is explicitly hypothetical: the book does not establish that starlings call more loudly to mislead rivals, or that their roost calls regulate clutch size. Its significance is analytical. Even evidence that aggregation and noise affect breeding need not vindicate group-level restraint; it could instead reveal information use and competition between individuals.

An Example in a Larger Argument

The starling discussion belongs to the book’s broader challenge to explanations that treat animal behavior as evolving for the good of a species or group. Its reasoning does not require denying that reproduction can respond to population density. Rather, it asks whether the behavior persists because it improves a group’s prospects or because individuals bearing particular genes leave more surviving offspring under the conditions they encounter.

The example’s force lies in keeping observation, hypothesis, and interpretation distinct. Large roosts are the proposed setting; a density-sensitive effect on spring egg-laying is an imagined result; individual adjustment and deliberate-seeming exaggeration are possible explanations, not reported findings. The account thus leaves starlings as a pointed case of evolutionary reasoning: a social-looking gathering may serve as a cue, while the consequences of that cue depend on whose reproductive interests the behavior ultimately advances.