DOI: 10.5061/dryad.tht76hf5v
title: The comparative effects of landscape-level forest fragmentation, forest area and local habitat measures on Connecticut bird communities

description: I studied how breeding and wintering forest bird communities across
 Connecticut responded to variation in habitat characteristics and
 particularly such landscape attributes as forest fragmentation. I surveyed
 birds at 1,815 points along 121 transects that traversed ca. 400 km of
 forest. I also made 12705 habitat measurements at survey points and
 computed areas of forest, non-forest, core forest and perimeter/area
 ratios of forest for 31,550 ha of study area. I computed sampled species
 richness and community density as well as individual species’ population
 densities for each transect. Moreover, I classified species encountered as
 to their nest site selection, macrohabitat use, microhabitat use,
 migratory strategy and trophic affiliation. Based on observations of
 36,702 summering individuals of 123 species and 13,742 wintering
 individuals of 63 species, declines in community density occurred with
 increasing fragmentation although species richness was often more closely
 associated with habitat measures. Among landscape measures, forest
 fragmentation had the closest association with summer community measures
 67% of the time, strongly suggesting that fragmentation effects were the
 predominant driver of such community patterns. However, short-distance
 migrant density and richness, foraging generalist density and richness,
 edge/successional species density and richness, habitat generalist
 density, and Brown-headed Cowbird density showed little relationship to
 landscape measures. The effects of fragmentation appeared to predominate
 over those of simply forest extent in predicting summer and winter bird
 community characteristics even in the comparatively extensive forests of
 southern New England. Despite the importance of fragmentation effects,
 community and individual species measures often tended to be more closely
 associated with habitat measures than with those of fragmentation. In
 addition, few summer or winter community measures or species patterns
 showed any significant relationship to natural forest breaks. 
 Winter community and species density patterns showed little relationship
 to any landscape measures, with particularly elevation appearing to be a
 principal driver of winter patterns.
description: I established 121 bird survey transects, with each traversing
 3.2−4 km of forest depending upon terrain and other local conditions. 
 Each transect had 15 survey points—the maximum I could visit during the
 peak of morning bird activity.  Routes began at first light (05:15 in
 summer, 07:00 in winter) and lasted 3.5−4 hr.  I used the Variable
 Circular Plot (VCP) technique to survey. I computed population densities
 with Distance 7.3 software. I visually evaluated
 habitat to a 70 m radius from each sampling station for: 1) forest type,
 2) moisture regime, 3) diameter of canopy trees at breast height (dbh), 4)
 canopy cover, 5) understory density and 6) elevation at the location of
 the survey point. I also summed canopy and understory measures to provide
 a measure of 7) vertical vegetation complexity. To characterize the
 landscapes within which the survey transects were situated, I employed
 QGIS 3.16 geographic information systems software to analyze aerial
 orthophotos. I plotted the survey points from each transect onto the
 photos and then constructed a 400 m wide buffer around the transect,
 thereby producing an 800 m wide corridor (averaging 260.7 ha area and
 covering 31,550 ha in sum for all transects) through which the transect
 passed. I chose this width because nearly all bird detections were within
 this corridor. In the corridor, I constructed polygons outlining each
 habitat present. Although pixel classification tools are frequently used
 for delineating habitats at this scale, I found that although doing so was
 more labor intensive, by visually comparing non-growing and growing season
 images and well as by relying on my familiarity with the study sites, I
 could construct digitized habitat polygons that maximized accuracy,
 precision and detail. 
description: # The comparative effects of landscape-level forest fragmentation, forest
 area and local habitat measures on Connecticut bird communities
 [https://doi.org/10.5061/dryad.tht76hf5v](https://doi.org/10.5061/dryad.tht76hf5v) The dataset contains summer and winter results of variable plot surveys of birds.  Column heads for survey data are: Global =  state location; Region = NECT (northeast CT), SECT (southeast CT), CECT (central CT), NWCT (northwest CT), SWCT (southwest CT); an additional S = summer and an additional W = winter; Season = summer, winter; Transect = transect number; Station = station number along transect; Species = U.S. Fish and Wildlife Service species code; Observation = distance from survey point in m; Flock = flock size for flocking species, otherwise = 1; Forest = 1 (deciduous), 2 mixed, 3 (conifer); Moisture = 1 (hydric, 2 (mesic), 3 (xeric); dbh = 1 (&lt; 15 cm), 2 (15-45 cm), 3 (&gt; 45 cm); Canopy = 1 (&lt; 40% cover), 2 (50-60% cover), 3 (&gt; 70% cover); Understory = 1 (&lt; 20% cover), 2 (30-60% cover), 3 (&gt; 70% cover); Elevation = elevation in m. Column heads for landscape measurements are: transect2 = transect number, map id = number given to a measured area on a GIS map, including buffer (entire map region), forest (forest cover), core forest (forest cover &gt;100 m from forest break), human (residential and urban cover), water (open water cover), field (agricultural land cover), beach (unvegetated lake or ocean shore cover), marsh (herbaceous wetland cover) ; area = area of the map region in m2; perimeter = perimeter of measured map region in m. xxxx codes indicate no birds detected at a winter survey point. Horizontal distances from the survey point are in meters and flock sizes for flocking species are in a separate column.  n/a codes and empty cells indicate no data.