Summary
To test whether alterations in aggressive behavior are responses to short-term resource depression, use of inexpensive and escalated territorial defense by Anna hummingbirds was analyzed as a function of the degree to which food could be depressed by foraging activities of territory owners and intruders. On depressible territories use of gorget display (a low cost defense) decreased and durations of chases increased as time since the previous feeding by owners increased. On non-depressible territories neither variable was significantly correlated with time since feeding. The percentage of intruders chased by owners was positively correlated with time since feeding on both depressible and nondepressible territories, but the magnitude of this trend decreased as food production increased. Departures from the territory tended to occur shortly after feeding on both types of territories, but this tendency was stronger on depressible territories.
When owners returned to their territories after long absences, gorget displays were used more frequenty and chases were shorter than after short absences, but no significant change occurred in the percentage of intruders chased. These results suggest that owners respond to intruder-caused resource depression by altering their use of gorget display and durations of chases, but not their frequency of chases.
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Ewald, P.W., Orians, G.H. Effects of resource depression on use of inexpensive and escalated aggressive behavior: experimental tests using Anna hummingbirds. Behav Ecol Sociobiol 12, 95–101 (1983). https://doi.org/10.1007/BF00343199
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DOI: https://doi.org/10.1007/BF00343199