DOES HUMAN INTRUSION ALTER THE SEASONAL TIMING OF AVIAN SONG DURING BREEDING PERIODS

The seasonal timing of male song during breeding affects the timing of territory establishment, male attraction, pair formation, egg laying, and transmission of information about breeding songs to young. Thus, alteration of the seasonal timing of song may influence reproductive s uccess and survivorship. Human intrusion has the potential to influenc e avian singing behavior. Accordingly, we determined whether repeated intrusion affected the seasonal timing of male song for three passerin es (Ruby-crowned Kinglet [Regulus calendula], Yellow-rumped Warbler [D endroica coronata], Dark-eyed Junco [Junco hyemalis]) in Wyoming fores ts. Intrusions involved one person walking through habitats for 1-2 h (Snowy Mountains, 1989-1993) or for 5 h (Pole Mountain, 1991-1993) eac h week for 10 consecutive weeks of each breeding season. For most comp arisons, we did not detect a significant difference in the seasonal ti ming of singing activity between control and intruded sites. Two excep tions were: (1) the mean singing date for Ruby-crowned Kinglets was 11 days earlier on intruded sites than on control sites at Pole Mountain ; and (2) the proportion of intruded sites with singing by Yellow-rump ed Warblers (0.40) was smaller than that for control sites (1.00) duri ng mid-June at Pole Mountain. Moderate and large differences in the ti ming of singing activity were detectable with a probability of 0.80, b ut small differences were not reliably detectable. Thus, our results a re a conservative estimate of the effects of intrusion on the seasonal timing of song. Curtailment of singing on intruded sites may have red uced breeding activity and, consequently, the quality of those sites f or producing young. Because intrusion-induced effects often are contex t-specific and can vary among individuals and species, and because our results are conservative, avian ecologists should continue to assess whether intrusion influences seasonal patterns of singing activity.