| dc.description.abstract | Effective conservation of biological diversity requires understanding of the
influences of habitat composition and structure on species and community composition.
Although patterns of bird richness and abundance in peatland natural communities have
been studied in Canada, little is known about these relationships in the United States,
especially within the Great Lakes region. Furthermore, environmental changes
associated with global climate change could significantly impact many natural
communities, including peatlands. Although potential impacts of climate change on birds
are poorly understood, species composition and habitat use by peatland bird communities
may be important to consider when monitoring peatlands for climate change impacts
because of the sensitivity of birds to changes in vegetation composition and structure. In
this study, I used several analytical methods to explain the distribution and habitat
relationships of peatland birds in relation to a suite of habitat variables measured at a
diverse array of peatland sites across Wisconsin.
In both 2006 and 2007, I surveyed peatland bird communities using standard
unlimited-radius point counts at 14 intensive sites and 74 extensive sites previously
selected by the WDNR. Intensive sites were non-randomly selected and surveyed ≥2
times each year of the study. Extensive sites were selected using a stratified random
sampling design and surveyed only once during the study. At both intensive and
extensive sites, point-count stations were established along a transect bisecting the
midsection of each peatland site. Vegetation was sampled at each point-count station
and the surrounding area following methods previously established by WDNR for the
multi-taxa peatland study. To supplement these vegetation data, additional habitat
variables were measured in 2007. Vegetation was surveyed at each point within the
intensive sites once per season in 2004, 2006, and 2007. Because extensive sites were
surveyed only once during the study, vegetation at these sites was surveyed immediately
after bird surveys. The area of each peatland site was determined using a Geographic
Information System (GIS).
I grouped bird species into 3 habitat-use guilds (forest, open-shrub, peatland-associated)
for analyses. Further, I grouped species as residents, short-distance migrants,
and neotropical migrants. Bird species present at ≥5% of sampling stations were selected
for individual analyses. I used three analytical methods to model bird habitat
relationships: logistic and linear regression and canonical correspondence analysis
(CCA). Data from both intensive and extensive sites previously collected by WDNR in
2004 and 2005 were included in analyses. I used stepwise logistic and linear regression
to analyze habitat relationships of 42 species with sufficient detections. Dependent
variables in models included species presence (logistic models) and mean abundance per
site (linear models), stratified by habitat association and migratory strategy. I also
analyzed habitat relationships of selected species that presently were near the edge of
their distribution range within the study area. Because of different sampling intensities
(i.e., years, number of point-count surveys/year) within intensive and extensive sites, I
modeled data from intensive and extensive sites separately. I also analyzed the 2007
extensive sites separately to examine potential differences resulting from including
additional habitat variables measured in 2007. I then examined bird community habitat
relationships using CCA, stepwise logistic and linear regression, as well as a priori
logistic and linear regression models with Akaike’s Information Criterion (AIC) model
selection.
Generally, significant variables common among analytical approaches indicated
that bird occurrence and relative abundance within peatlands increased in response to
greater cover and structural diversity of shrub strata. Among logistic and linear
regression models selected using AIC, models containing the variables snags, percent
cover of low shrubs and high herbs, peatland area, and percent cover of all conifer trees
received the strongest empirical support. Overall, foliage height diversity within
peatlands appeared to be the most important structural attribute contributing to bird
diversity and abundance within these habitats. In addition to providing a better
understanding of peatland bird habitat relationships within the Great Lakes region, the
results of this study may provide managers with important baseline data that could be
used to monitor potential effects of climate change on peatland flora and fauna. | en_US |
