PROVISIONING PATTERNS, DIET, AND REPRODUCTION OF MOUNTAIN BLUEBIRDS (SIALIA CURRUCOIDES) IN CLEARCUT VERSUS GRASSLAND HABITATS
Stalwick, Jordyn A 1993-
Clearcutting of forests results in early successional stages that resemble grasslands, and grassland birds such as mountain bluebirds (Sialia currucoides) may settle in these habitats during the breeding season. I had two main objectives in my study: 1) to determine if clearcuts are less productive habitats compared to grasslands regarding the amount and quality of prey; and 2) to test nestling gape size as a mechanism that limits parents’ provisioning abilities. Mountain bluebirds feed their nestlings prey such as larvae, spiders, and beetles. To determine what prey items parents were bringing, I placed microcameras in the nestboxes to film parental food deliveries. I found that parents in clearcuts brought larger, more nutritious prey than parents in grasslands but had a lower delivery rate. This lower delivery rate could indicate that prey was less abundant in clearcuts compared to grasslands, although arthropod abundance surveys need to be conducted to add confidence to this conclusion. Adult bluebirds that settled in clearcuts did not differ in age or quality from those that settled in grasslands. Most reproductive parameters did not differ between habitats although fledglings in grasslands weighed more than fledglings in clearcuts. Clearcuts may be ecological traps based on foraging potential because bluebirds settled in both habitats equally but had nestlings of lower quality in clearcuts (potentially affecting the nestlings’ chances at survival). Finally, by observing parents feeding nestlings, I found that when parents brought larger prey items, they attempted to feed a nestling but withdrew the prey item from the nestling’s gape more often than when offering smaller prey items. The smallest nestling of a brood was fed less often when parents brought large prey items. Patterns of prey allocation within broods were similar between clearcut and grassland habitats. Therefore, while prey volume and type differed between the two habitats, hatching asynchrony did not amplify these prey differences’ effects on the swallowing ability of nestlings. In sum, clearcuts may be lower-quality habitats than grasslands, but settling in clearcut habitats may be a better alternative for mountain bluebirds compared to not breeding at all, if the availability of natural grassland habitats decreases.
DegreeMaster of Science (M.Sc.)
SupervisorWiebe, Karen L
CommitteeClark, Bob; Morrissey, Christy; Bayne, Erin; Wei, Yangdou
Copyright DateJuly 2018
habitat, ecological trap