INTRUSIONS, AND RESIDENT PAIR RESPONSES, DURING THE BREEDING CYCLE OFTHE ORANGE-CROWNED WARBLER

I observed Orange-crowned Warbler Vermivora celata behavior at or near 40 nest sites over 287 h during the nest construction, egg laying, in cubation, nestling, and/or fledgling stages. I recorded intrusions mos t frequently during nest construction (2.14 h-1), less frequently duri ng late nestling care (day seven through fledging, 0.81 h-1) and after fledging (0.89 h-1), and infrequently during incubation (0.07 h-1) an d early nestling care (the first six days, 0.10 h-1). I also recorded a moderate mean intrusion rate during egg laying (1.30 h-1), based on relatively few observations. I recorded interactions between resident males (RMs) and intruders most frequently during nest construction (1. 63 h-1), less frequently during late nestling care (0.48 h-1) and afte r fledging (0.28 h-1), and infrequently during incubation (0.05 h-1) a nd early nestling care (0.06 h-1). I recorded interactions between int ruders and resident females (RFs) most frequently during late nestling care (0.30 h-1), less frequently during nest construction (0.21 h-1), and infrequently during incubation (0.01 h-1), early nestling care (0 .02 h-1), and after fledging (0.02 h-1). Intrusion rates and RM-intrud er interactions varied significantly among nest sites during both nest construction and late nestling care. During nest construction, RMs de monstrated ''waiting,'' ''following,'' and ''close feeding association '' behaviors, all of which may function to guard the RF from intruders . I also observed waiting during nestling care, and close feeding asso ciations during all breeding stages. Resident pairs (RPs) tending nest lings after day six may demonstrate ''coordinated'' feeding of nestlin gs more often at intruded nest sites than at non-intruded nest sites. Coordinated feeding of young is correlated with RP waiting at nest sit es, and may facilitate mate guarding. I discuss identity of intruders, and possible explanations for intrusions, and RP responses, during la te breeding stages, when RFs may be infertile. I suggest that sexual m otivation best explains at least some of these behaviors.