Graduate Thesis Or Dissertation


An Assessment of Black-backed Woodpecker (Picoides arcticus) Vital Rates in Green and Burned Forests within a Pyrodiverse Landscape Mosaic Public Deposited

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  • Vital rates and population connectivity are fundamental concepts in animal ecology and such information is critical for successful conservation planning. The Black-backed Woodpecker (Picoides arcticus) is a species of conservation concern because of its strong association with forests recently burned by high-severity wildfire. However, several recent studies have found that Black-backed Woodpeckers use unburned forest (hereafter, green forest) as nesting habitat in California and Oregon, raising questions about the extent to which vital rates differ between green and burned forests, as well as the role green forests play in supporting regional populations. Given these knowledge gaps, we studied the breeding ecology of Black-backed Woodpeckers in south-central Oregon in green and burned forests to compare two key vital rates that underpin population dynamics – nest survival and post-fledging survival. During the 2018, 2019, and 2021 breeding seasons we monitored 94 Black-backed Woodpecker nests (n = 33 in green forest, n = 61 in burned forest) and found, against our initial predictions, that probability of nest success rates were similar between nests located in green forest (81.6% [95% CI: 61.4, 91.9%]) and in burned forest (71.0% [95% CI: 51.7, 83.7%]); the main cause of nest failure in both forest types was predation. We also found similar measures of reproductive output (green forest: 2.30 [95% CI: 1.93, 2.68] fledglings per successful nest; burned forest: 2.30 [95% CI: 2.06, 2.53] fledglings per successful nest), and body condition of nestling Black-backed Woodpeckers in green and burned forest. Additionally, we found no evidence for an effect of nest-site characteristics on nest survival, clutch size, or nestling body condition; instead, nest initiation date had the greatest influence on these measures. We found that egg hatchability and the number of offspring to successfully fledge were moderately influenced by cavity height and tree size (as measured by diameter at breast height), respectively. In addition to nest-site based measures, we also quantified survival of recently fledged individuals using VHF radio telemetry tags and found that post-fledging survival in green forest (0.654 [95% CI: 0.489, 0.875]) was nearly identical to that in burned forest (0.650 [95% CI: 0.494, 0.855]). Our results provide the first comparative data for Black-backed Woodpecker vital rates in undisturbed green and burned forests of the western United States and establishes that vital rates do not vary meaningfully between these forest types in south-central Oregon. Our research suggests that green forest provides key breeding habitat for the Black-backed Woodpecker. This has important implications for their conservation given that in the western United States, green forest occupies the majority of the forest landscape relative to areas burned by wildfire in the past 20 years. Thus, forest management practices that promote pyrodiversity and connectivity between green and burned forests should be considered for landscape-level management. Such comprehensive management strategies will likely benefit Black-backed Woodpecker populations in south-central Oregon and other areas in the western part of its geographic range.
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