Prospecting in a solitary breeder: chick production elicits territorial intrusions in common loons

In many species, young animals learn about various breeding patches in one year and use what they have learned to settle in a promising patch the next. Common loons (Gavia immer) seem good candidates for such prospecting as prebreeders and displaced breeders intrude frequently into breeding territories defended by monogamous pairs yet engage in no extrapair copulations. We tested 3 hypotheses for prospecting in loons. The permanent attributes hypothesis gained little support as we found no consistent differences in quality between territories and no physical or biotic trait that predicted reproductive success in a territory. We found some support for the conspecific attraction hypothesis as intruders were attracted to conspecifics in a lake in the short term; however, intrusions were not more frequent in territories that had experienced regular use by a pair the previous year than in territories that had previously been vacant. Instead, the increase in intrusion rate after a year of chick production supported the habitat-copying hypothesis, which states that floaters use the presence of chicks as a cue to target territories for future attempts at territorial takeover. Despite this system of prospecting, founding of new territories was common. One striking finding was the tendency of territorial breeders to conceal chicks from flying intruders, perhaps to avoid future territorial takeover. Copyright 2006.