Time Budgets of the Willow Flycatcher in the Central Sierra Nevada in Relation to Nest Success

MASTERS THESIS: The willow flycatcher (Empidonax traillii) used to be a common summer resident in and throughout California, however the California population has declined over the past 40 to 50 years. Several factors have contributed to the decline in their abundance including loss of habitat in riparian zones, grazing, road building, and nest predation. Observing survival and how individuals allocate time can provide insight into a species’ ability to survive under these particular constraints and can allow for an evaluation of its tolerance to such constraints. In this study, I determined the time budgets of the central Sierra Nevada willow flycatcher, examined the relationship between the breeding success of Sierra Nevada willow flycatchers and their behavioral activities, and compared environmental conditions to time allocation. I used instantaneous sampling for measuring the time allocation of 10 different activities throughout the breeding season. I pooled data from the two observed breeding seasons (200-2001). I observed time budgets of the remaining 32 territories. In general, willow flycatchers spent a majority of their time throughout the breeding season perching. This large amount of perching classifies the willow flycatcher as a ‘time minimizer.’ The average time singing was the highest during the egg laying phase, then dramatically dropped off during the incubation and nestling phases. Average foraging time was doubled during the nestling phases over the other four phases since they have to meet the daily intake requirements of not only themselves, but their young as well. Observed territories failed during the nest building, incubation, and nestling phases. I used a one way T-test to determine any relationships between the behavior of birds in successful and unsuccessful territories. Territories that successfully made it through the incubation stage contained individuals that spent on average less time singing and perching and more time on the nest than territories that were unsuccessful during that stage. During the nestling phase, successful territories contained individuals that spent on average less time perching. Simple linear correlation was used to determine the relationship between the rates of activities and the environmental factors of wind speed, ambient temperature, cloud cover, and precipitation During 3 of the 5 phases of the breeding season, temperature increase was correlated with increased foraging. During the territory establishment phase, males spent more time perching with increased wind speed, cloud cover, and temperature.