My
primary research interests revolve around factors
that influence habitat quality, in particular food
availability, and songbird response to such variation.
Since migration represents a period of heightened
energetic demand, studies conducted during migratory
passage provide an ideal setting in which to examine
constraints placed on food resource acquisition by
migrant passerines. At each stopover site, migrants
may encounter varying factors influencing food resource
use, including a forager’s fat reserves, predator
activity, and competition. Theoretical models on
the consequences of environmental unpredictability
conclude that disparate behaviors during periods
when expected fitness is highly variable are most
advantageous, minimizing the uncertainty associated
with changing external conditions, like those encountered
from one stopover site to the next (Real 1980). Thus,
the migratory period may select for behavioral plasticity,
defined here as the ability of individuals of the
same genotype to vary in phenotype in accordance
with environmental change (Greenberg 1990). Shifts
in foraging behavior and diet may reflect compensatory
mechanisms for satisfying the elevated energetic
demands of migration in the face of a specific set
of constraints.
My research
seeks to examine constraints on resource acquisition
and migrant response to such restrictions along the
northern coast of the Gulf of Mexico at three spatial
scales: landscape (across habitat types), patch (coarse
features within a habitat patch), and microhabitat
(fine features within a habitat patch). Using both
observational and experimental approaches, I hope
to address questions like the following:
Do
migrants diversify their foraging behavior
to compensate for declines in food resource availability?
Does
a migrant’s energetic condition (subcutaneous
fat deposits) influence its response to changes
in prey availability?
Do
migrants alter their foraging behavior with changes
in habitat structure?
Does
migrant density influence the rate of decline in
prey abundance?
Does
predation by migrants influence arthropod community
composition through shifts
in overall insect behavior, activity patterns,
and level of crypsis?
Does
temperature influence the activity, and thus availability,
of insect prey?
What
factors influence the incidence of frugivory during
migratory passage?
Effects of Local- and Landscape-scale Variation
on the Distribution of Three Area-sensitive Forest
Songbirds in Vermont (University of Vermont 2003)
As a landscape
becomes increasingly fragmented, average forest tract
size decreases, leaving
area-sensitive bird
species vulnerable to loss of suitable habitat because
they avoid small patches and edge habitat. Landscape-level
fragmentation may further influence the amount of
quality habitat through alteration of patch-level
processes
and community composition. It is, therefore,
important to understand
the multiple factors, at both the local- and landscape-scale,
that may influence habitat quality. I examined distribution
and abundance of three area-sensitive songbirds,
Black-throated Blue Warbler (Dendroica caerulescens),
Ovenbird (Seiurus
aurocapillus), and Red-eyed Vireo (Vireo
olivaceus),
across a gradient from edge to interior habitat
in forest patches
located in landscapes with three different levels
of fragmentation. Relative abundance of all three
species increased with
distance from the edge, a response that appeared
to
be magnified by decreases in forest cover in
the surrounding
landscape. I also quantified habitat quality at the
patch level through measures of vegetation
characteristics and
prey abundance and biomass. Biomass of both ground
arthropods and Lepidoptera larvae was higher
in edge habitat, and
larval abundance and individual biomass was greater
in the most fragmented landscape type. Of the
vegetation characteristics,
understory woody stem density and canopy cover decreased
and ground cover increased with distance from the
edge, while understory woody stem density increased
with
landscape-level fragmentation at distances
closest to the forest edge.
I, therefore, recommend consideration of both local-
and landscape-scale habitat variables when
determining appropriate
conservation strategies for area-sensitive forest
songbirds in the region.
Greenberg, R. 1990. Ecological plasticity, neophobia, and
resource use in birds. Studies in Avian Biology 13:
431-437.
Real, L. A. 1980. Fitness, uncertainty,
and the role of diversification in evolution and behavior.
American Naturalist
115: 623-638.
Department of Biological Sciences
The University of Southern Mississippi
118 College Drive # 5018
Hattiesburg, MS 39406-0001
(601)266-4394
megan.e.hughes@usm.edu
