Date of Award
Master of Science (MS) in Biology
Primary cavity-nesting birds are keystone species because the annual tree cavities they excavate become critical habitat for other species. In eastern Washington, most primary cavity-nesting birds are year-round residents. They increase overwinter survival by night roosting in cavities and forming flocks. The timing of roost site selection can impact the quality of a roost site, thus selecting a roost site too late reduces the odds of selecting the most favorable microclimate available. Birds in flocks use alarm calls to warn of threats and contact calls to promote group cohesion. My study asks if timing of roost site selection and vocalizations influence the frequency and flock size of cavity- nesting birds inspecting roosting sites and if flock size varies with temperature. The study was conducted during the winters of 2016-17 and 2017-18 on Turnbull National Wildlife Refuge. Roost boxes were located at 36 stations divided between 3 forest units. At each station, I conducted an 8-minute point count prior to sunset. Following the initial point count, I conducted a second point count with 1 of 3 broadcast treatments: 1) no call 2) alarm call and 3) contact call. I compared the number of cavity-nesting birds observed and mean temperature to time before sunset using a Chi-squared test and t-test, respectively. I compared the mean differences in the number of birds observed between initial and treatment point counts and the frequency of point counts in which species’ were present between treatments with an ANOVA and a Fisher’s exact test, respectively. I examined the effect of temperature on flock size using Poisson regression. During the 2016-17 winter, I recorded 516 observations of 8 species and during the 2017-18 winter 730 observations of 9 species. In 2016-17 there was an increase in birds present during the 105 - 0 minutes before sunset time period and in 2017-18 more birds were observed during the 210 – 105 minutes before sunset time period. Mean temperatures were significantly colder during both time periods in 2016-17. The number and presence of pygmy nuthatches increased following contact call treatment for both winters. The presence of chickadees increased following alarm and contact call treatments in 2016-17 and alarm call treatment in 2017-18. The number of black-capped and mountain chickadees increased following the alarm call treatment, and red-breasted nuthatches increased following the alarm and contact call treatments in 2017-18. As temperature decreased flock size increased in 2017-18. Timing of roost site selection varied with abiotic conditions. Vocalizations influence roost selection for some cavity-nesting birds
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Hunter, Shelby M., "Vocalizations influence roost-site selection in overwintering cavity-nesting birds in Eastern Washington" (2018). EWU Masters Thesis Collection. 498.