Using population and habitat analyses at multiple spatial scales to address New Hampshire statewide Canada warbler (Cardellina canadensis) declines

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Martin, Mysti
The Canada warbler (Cardellina canadensis) is a Neotropical-Nearctic species of special conservation need currently experiencing declines across its breeding range, especially within New Hampshire according to the Breeding Bird Survey (BBS). They are most abundant in forested wetlands and in regenerating early-successional forests from 5 - 20 years post harvest. Aging forests and development in New Hampshire likely contribute to declines observed in the statewide census. BBS surveys occur along roadsides where development and forest fragmentation may bias sampling and overlook populations in more long-term suitable habitat such as extensive forested wetlands. Monitoring Canada warbler populations at various spatial scales may help determine whether statewide BBS trends disproportionately measure fragmentation/development effects. We examined approximately 10 years of population and vegetation data within a contiguous forested landscape across central New Hampshire at three spatial scales: neighborhoods (100 ha), metapopulations (376 ha), and regional National Forest (3160 ha). Data analyses indicate that at these scales populations are not declining significantly. We compared slopes and intercepts of the population analyses among neighborhoods, regional and statewide BBS and found no significant difference among trends. While the metapopulation scale needed to be analyzed differently, results corroborate findings at the other spatial scales. Habitat characteristics at the neighborhoods scale indicate pockets of sustained suitable Canada warbler habitat with stable populations, which may be underrepresented along BBS routes. Thus, population trends exhibit different profiles at varying spatial scales. Larger spatial scales may help identify species of priority, while smaller spatial scales may help determine areas of conservation priority.