Occurrence of the Connecticut Warbler Increases with Size of Patches of Coniferous Forest

Abstract

The Connecticut Warbler {Oporornis agilis) is a rare and declining neotropical migrant that breeds in the north-central United States and south-central Canada. To better understand the species' habitat needs, we analyzed 371 observations of the Connecticut Warbler over 18 years at 86 sites in 28 stands of forest in northern Minnesota. We considered the habitat and landscape at three spatial scales (buffer radii of 100, 500, and 1000 m) and regressed combinations of habitat variables with two response variables, the Connecticut Warbler's abundance (the total number of individuals ever recorded at a site or stand, with a zero-inflated negative binomial distribution) and frequency (the number of years recorded out of 18, with logistic regression). From a subset of models retained on the basis of Akaike's information criterion, we calculated model-averaged predictions for each combination of buffer size and response variable. Models based on Connecticut Warbler frequency at the 1000-m buffer performed best in comparisons of model-averaged predictions to observed data. At the 1000-m scale, Connecticut Warblers were positively associated with a combination of large patches of upland coniferous and lowland black spruce forest and were negatively associated with upland deciduous forest. From these models, we mapped predicted breeding habitat for the Connecticut Warbler in the areas sampled in northern Minnesota.

Habitats and landscapes associated with bird species in a lowland conifer-dominated ecosystem

“…GAP level 4 data were reclassified into 18 land cover types hypothesized to affect bird species breeding in lowland coniferous habitats (Table 1). A variety of metrics of landscape pattern similar to those used in previous modeling efforts for these species were derived from the reclassified GAP data (Hawrot and Niemi 1996, Drolet et al 1999, Crozier and Niemi 2003, Lapin et al 2013), but many were highly correlated and only patch richness and number of patches were retained for analysis. Individual patches were defined as contiguous (eight grid cell, nearest neighbor) units of GAP level 4 land cover data.…”

“…Despite this, only one study has completed a detailed analysis of Connecticut Warbler breeding habitat in Minnesota. In the Superior and Chippewa National forests, Lapin et al (2013) found the Connecticut Warbler primarily in large contiguous patches of lowland conifer forests often surrounded by upland coniferous forest, as opposed to upland deciduous forest. Models with local stand variables (100 m buffer), including detailed measurements of forest stand characteristics such as tree and shrub density, performed poorly.…”

“…forests. More recent work in Minnesota has shown that this species is associated with large patches of lowland conifer adjacent to upland conifer forests (Lapin et al 2013). However, to better inform forest management and forest planning, additional information regarding specific tree species, age classes, and structural characteristics utilized by species breeding in lowland conifer forests is desirable.…”

“…We examined the characteristics of these species' breeding habitat by developing and testing a method for modeling habitat suitability across the lowland conifer forests of the ALS. Past research in this region has generally focused on stand-level habitat metrics or cover types, i.e., dominant tree or other vegetative composition, for determining associations for these species (Dawson 1979, Niemi and Hanowski 1984, Warner and Wells 1984, but see Hawrot and Niemi 1996, Crozier and Niemi 2003, Lapin et al 2013. Here, we used a subset of both standlevel and landscape environmental variables predicted to affect the distribution of species breeding in lowland conifer forests (Table 1).…”

“…In particular, each species was expected to select for certain types of lowland conifer forest and different scales of landscape variables within lowland conifer forests of the ALS (Table 2). Pitocchelli et al (2012), Lapin et al (2013) Palm Warbler (Setophaga palmarum) (+) Stagnant black spruce, (+) stagnant tamarack, (+) Black spruce/tamarack, (-) basal area Niemi and Hanowski (1984), Warner and Wells (1984), Wilson (2013) Dark-eyed Junco (Junco hyemalis) (+) Black spruce, (+) evergreen, (+) stagnant lowland conifer Erskine (1977), Warner and Wells (1984), Hobson and Bayne (2000) To identify potential areas for conservation, we overlaid models for five species of conservation concern and ranked grid cells by the number of species predicted to have suitable breeding habitat. This study provides a valuable methodological framework for managers seeking to identify breeding habitat and potential conservation areas at regional or landscape scales.…”