Begging

(for attracting predators yields a prediction:)

for attracting predators yields a prediction:

(Baby birds of species that experience high rates of nest predation should produce softer begging signals)

Baby birds of species that experience high rates of nest predation should produce softer begging signals

(of higher frequency than nestlings of other species less often victimized by nest predators.)

of higher frequency than nestlings of other species less often victimized by nest predators.

(This prediction was supported by data collected in one survey of 24 species from an Arizona forest,)

This prediction was supported by data collected in one survey of 24 species from an Arizona forest,

(more evidence that predator pressure favors the evolution of begging calls)

more evidence that predator pressure favors the evolution of begging calls

(that are hard to detect and pinpoint.)

that are hard to detect and pinpoint.

(Given that predators can make it costly to beg for food,)

Given that predators can make it costly to beg for food,

(what benefit do begging nestlings derive from their communications?)

what benefit do begging nestlings derive from their communications?

(One possibility is that a noisy baby bird provides accurate signals of its real hunger and good health,)

One possibility is that a noisy baby bird provides accurate signals of its real hunger and good health,

(making it worthwhile for the listening parent to give it food in a nest where several other offspring)

making it worthwhile for the listening parent to give it food in a nest where several other offspring

(are usually available to be fed.)

are usually available to be fed.

(If this hypothesis is true, it follows that nestlings should adjust the intensity of their signals)

If this hypothesis is true, it follows that nestlings should adjust the intensity of their signals

(to the signals produced by their nestmates, competing for parental attention.)

to the signals produced by their nestmates, competing for parental attention.

(When experimentally deprived baby robins are placed in a nest with typically fed siblings,)

When experimentally deprived baby robins are placed in a nest with typically fed siblings,

(the hungry nestlings beg more loudly than usual.)

the hungry nestlings beg more loudly than usual.

(But so do their better-fed siblings, though not as loudly as the more famished birds.)

But so do their better-fed siblings, though not as loudly as the more famished birds.

(If parent birds use begging intensity to direct food to healthy offspring capable of vigorous begging,)

If parent birds use begging intensity to direct food to healthy offspring capable of vigorous begging,

(then parents should make food delivery decisions based on their offspring's calls.)

then parents should make food delivery decisions based on their offspring's calls.

(Indeed, if you take baby tree swallows out of a nest for an hour,)

Indeed, if you take baby tree swallows out of a nest for an hour,

(feeding half the set and starving the other half,)

feeding half the set and starving the other half,

(when the birds are replaced in the nest, the starved youngsters beg more loudly than the fed birds,)

when the birds are replaced in the nest, the starved youngsters beg more loudly than the fed birds,

(and the parent birds feed the active beggars more than those who pray less vigorously.)

and the parent birds feed the active beggars more than those who pray less vigorously.

(As these experiments show, begging provides a signal of need that parents use to judge which offspring)

As these experiments show, begging provides a signal of need that parents use to judge which offspring

(can benefit most from feeding.)

can benefit most from feeding.

(But the question arises: why don't nestlings beg loudly when they aren't all that hungry?)

But the question arises: why don't nestlings beg loudly when they aren't all that hungry?

(By doing so, they could secure more food, which should result in more rapid growth or larger size,)

By doing so, they could secure more food, which should result in more rapid growth or larger size,

(which is advantageous.)

which is advantageous.

(The answer lies not in the increased energy costs of exaggerated begging.)

The answer lies not in the increased energy costs of exaggerated begging.

(Such energy costs are small relative to the potential gain in calories,)

Such energy costs are small relative to the potential gain in calories,

(but in the damage any successful cheater would do to its siblings, which share genes.)

but in the damage any successful cheater would do to its siblings, which share genes.

(Individuals' success in propagating their genes can be affected)

Individuals' success in propagating their genes can be affected

(by more than just their reproductive success.)

by more than just their reproductive success.

(Because close relatives have many of the same genes,)

Because close relatives have many of the same genes,

(animals that harm their close relatives may be destroying some of their own genes.)

animals that harm their close relatives may be destroying some of their own genes.

(Therefore, a begging nestling that secures food)

Therefore, a begging nestling that secures food

(at the expense of its siblings might leave behind fewer copies of its genes overall than it might otherwise.)

at the expense of its siblings might leave behind fewer copies of its genes overall than it might otherwise.