Scientists creating fake crises at bird nests have confirmed a theory about
parents protecting themselves at their offspring’s expense.
According to theorists, this type of behavior should occur in species that live
relatively long and bear only a few young at a time. Species with shorter lives
and that produce more offspring per batch should take the opposite path: Parents
ought to risk their own lives for the sake of offspring. Field studies have
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confirmed these proposed behavior patterns, say Cameron K. Ghalambor of the
University of California, Davis and Thomas E. Martin of the University of Montana
They analyzed life patterns for 182 songbirds. Southern Hemisphere species tend to
live longer and lay smaller clutches than northerners, the researchers report in
the April 20 Science. Ghalambor and Martin identified five pairs of species with
similar ecology but living in opposite hemispheres. For example, they matched a
robin with a rufous-breasted thrush.
Playing calls of hawks, which eat adult birds, near a nest prompted more self-protective behavior among the southern species. These birds, with a smaller
relative investment in any particular clutch than their northern counterparts,
chose to avoid feeding runs and remain hidden, even though their young went
hungry. The northern birds, however, risked such runs.
When these braver parents heard calls of a jay, which kills nestlings but not
adults, they curtailed feeding runs, which might have revealed their nest’s
location. However, their less invested counterparts hazarded such trips, the