A male common loon, Gavia immer, guards his 10-day old
chicks while his mate forages away from the family. Territorial
pairs face a 50% increase in intrusions in the year after they
produce chicks, because unmated adults of both sexes use the
presence of chicks as a cue to target territories for takeover
attempts (see Piper et al., pp. 881-888). Photo by W. Hagge.
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