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Problem/Background
Modern organophosphate
insecticides are short-lived in the environment. These insecticides are
toxic to raptors, but they are unlikely to be detected in animal blood
or tissue unless the animals are sampled soon after exposure. Researchers
postulate that pesticide exposures, and habitat alteration,  in
their wintering areas in Central and South America may be adversely affecting
broad-winged hawk (Buteo platypterus, BWHA) populations, and those of
other neotropical migrants. However, it is unknown whether broad-winged
hawks concentrate in certain areas in their winter range and what specific
biological threats they might be exposed to during this part of their
annual cycle. Essentially, the extent to which conditions encountered
in the winter range affect the populations that breed in North America
is unknown. This is largely because very little is currently known about
the wintering ecology of this small, forest-dwelling raptor
.
The broad-winged hawk
is a neotropical migrant that breeds in eastern and central North American
forests and winters primarily from Southern Mexico south through Central
America to northern South America (Bolivia and Northern Brazil), with
small numbers wintering in southern Florida. Its population status is
of concern due to the decline in numbers of birds encountered at some
migration observation points since the 1970’s and in some areas
of its breeding range in the Eastern United States. Information is available
on the natural history of the broad-winged hawk in North America, but
little is known of its wintering ecology. Within the continental United
States, breeding numbers appear to be stable in some areas but decreasing
in others. The Puerto Rican population is classified as Endangered, and
these declines are attributed to habitat alterations. Similarly, in the
Eastern United States, some areas have reported declines in BWHA associated
with human development and alteration of woodlands.
 Approach/Objectives
Earthspan’s broad-winged
hawk research focused on identifying critical habitat during the breeding
season, along migration pathways, and during the boreal winter period.
The approach integrated radio tracking via satellite, field monitoring,
remote sensing, and a geographical information system (GIS) to identify
locations and important landscape and nest site features used by the species.
This study filled gaps in knowledge concerning aspects of broad-winged
hawk migration and wintering biology and provided data critical for the
development of a management plan for broad-winged hawks on federal, state,
and private lands throughout its annual range
.
Results
Because broad-winged
hawks tend to travel in large flocks that are easily identified on NEXRAD
radar imagery, Earthspan and the Clemson University Radar Ornithology
Laboratory are attempting – for the
first time ever – to correlate migration data of individual BWHAs
with flock activity. Results from this study will be useful in the development
of an effective resource management strategy for this species that can
be applied throughout the Americas. Additionally, information collected
about land use practices and environmental contaminant uses will be relevant
to the conservation of a variety of other wildlife species.
Earthspan tracked (via
satellite) broad-winged hawks from North America to their wintering areas
and described important land cover types at the hawks' destinations (both
breeding and wintering). Our research provided information on the extent
to which North American nesting populations associate with natural and
modified habitats across the non-breeding range. Additionally, information
may be acquired to describe their exposure to habitat alteration and environmental
contaminants in their wintering areas. The breeding habitat, migratory
pathways, and wintering range of broad-winged hawks are also shared by
a number of other neotropical migrant species, including several that
are species of major conservation concern. This project will set the standard
for other research projects to study the movements, migration, and wintering
habitats of other neotropical migratory species.
Resulsts from this
project were published in The Wilson Quarterly.
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