Summary
We tested whether payoff asymmetries could explain why "floater" red-winged blackbirds seldom escalate contests to acquire territories. We removed territorial male "owners" and allowed floater replacements to claim territories. We then released owners to see how three currencies of payoff asymmetries (replacement occupancy time, owner familiarity with neighbors, and owner reproductive investment) affected owners' likelihood and speed of reclaiming their territories (owner success). Neither the duration of an owner's internment nor the amount of time that a floater replacement had held the territory affected owner success (Figs. 1 and 2). Owner success was also not affected by the number of neighbors that they had (Fig. 3). Finally, owner success was the same irrespective of whether or not he was the likely sire of offspring on the territory, or the size of his harem (Fig. 4). Although these results are consistent with the proposal that payoff asymmetries will be irrelevant in contests for valuable resources, they are inconsistent with the proposal's corollary that excluded individuals should become "desperados" and escalate or even fight to the death in contests for those resources. Expected payoffs for passive acquisition of territories in this species may be higher than from a more aggressive desperado strategy.
Methodology
Our study area was near the Queen's University Biological Station in southeastern Ontario. Our population of redwinged blackbirds occupied territories spaced irregularly in ditches beside rural highways. Approximately half of the males in our population are floaters (Shutler and Weatherhead 1991 a). Consequently, vacancies are usually claimed within a day. Our protocol was to compare owners' ability to reclaim their territories relative to each of the currency values. We performed removal experiments in which male territory occupants were captured using stuffed male decoys and playback with traps (Smith 1972) or mist nets. Removals were done in the morning from early 99 April (pre-nesting) to late June (late nesting) in 1988, 1989, and 1990. Beyond late June there were no new nest initiations and territory occupants no longer responded to decoys. Removed males were banded, and then held captive in one of six outdoor 3 x 2 x 1.5 m aviaries at the Biological Station. A maximum of ten males occupied an aviary at any time. Captive males were supplied water and food ad libitum and were held for between 2 and 30 days. Removed males were usually replaced on their territories by males that had previously been floaters, and less often by neighbors (Shutler and Weatherhead 1991 a). In most cases, as part of a larger study, we attempted to remove floater replacements as well. Replacements were housed with the territory owner (see Shutler and Weatherhead 1991a for details). We continued to remove males until a replacement failed to respond to a decoy, or less commonly, no additional replacements occurred within 12 days after a removal. Once either situation occurred, "final" replacements were allowed to occupy the territory undisturbed. The largest number of males removed from a territory was ten. In all cases, replacements were released back at the territory from which they had been captured before or at the same time as the owner. In all cases, released individuals flew out of sight immediately or were driven off by the territory occupant within 5 rain (also see Beletsky and Orians 1987). However, in many cases released individuals did eventually reclaim their territories (see below). Because the timing of territory reclamation was unpredictable, we were unsuccessful in our attempts (15 observation periods of up to 2 h) to observe a reclamation in progress. However, we were able to determine all cases in which a released male successfully reclaimed his territory.