Illinois Natural History Survey Reports

              1
I LLINOIS
NATURAL
HI STORY
S U R V E Y R e p o r t s
May/
June 1998
No. 351
I N S I D E
Long-term Dormancy
in Freshwater
Zooplankton
2
Wetland Bird Conser-vation
in Northeastern
Illinois
3
Illinois Earthworms: In-dicators
of Soil Health?
4
Species Spotlight:
Passenger Pigeon
6
The Naturalist's
Apprentice:
Passenger Pigeon
Colors
7
Continued on back page
A fox snake, one of several predators of songbirds.
Much of the natural habitat of
the midwestern U.S. has been
converted to agricultural use. In
east-central Illinois, for example,
row-crop agriculture covers
about 75% of the land area and
dominates the landscape. The
remaining natural areas are also
typically highly fragmented,
creating large amounts of edge
habitat. Recent conservation
literature has focused primarily
on the negative aspects of such
habitat fragmentation, but some
species thrive in these heteroge-neous
areas. In fact, medium-sized
mammalian predators, such
as coyotes, raccoons, and opos-sums,
have increased to what are
probably historic high densities
in Illinois in the past few decades
despite extensive conversion of
natural habitats to agriculture.
These species tend to be very
opportunistic in their choice of
food and habitat, as long as cer-tain
basic requirements, such as
suitable den sites, are met. Some
recent studies have shown that
raccoons reach their highest num-bers
in landscapes with extensive
agricultural edges, in wooded
remnants in areas with extensive
corn cover, and in fragmented
landscapes with a high diversity
of cover types, especially where
there is proximity to water.
The good news for some kinds
of animals can be bad news for
others, though. Predators may
use habitat edges as travel lanes
or forage more intensely there,
elevating rates of predation on
songbird nests. In some areas
of the Midwest where habitat
fragmentation is extensive, rates
of predation and nest parasitism
by cowbirds can be so high that
Don't Blame It All on the Raccoons
nesting song-birds
do not
fl edge enough
young to main-tain
stable pop-ulations.
These
areas may be
population
sinks for song-birds,
meaning
that popula-tions
must be
maintained by
constant immi-gration.
Many
kinds of preda-tors
take song-bird
nests, but at
least two studies
in the Midwest
have implicated
the raccoon as
the major preda-tor
in agricul-tural
regions.
So far, though,
few data show
how different types of predators use
habitat edges.
At the Middle Fork Fish and
Wildlife Area in Vermilion County,
we radio tracked 15 raccoons and
4 opossums to determine whether
they used habitat edges preferen-tially.
We also conducted experi-ments
using wicker nests baited
with commercial quail and Zebra
Finch eggs to determine if rates
of predation differed in fi elds of
different sizes (are predation rates
lower in large fi elds?) or at differ-ent
distances from habitat edges
(are predation rates higher closer to
the edge than out in the middle of
the fi eld?). This research is part of
a Federal Aid in Fish and Wildlife
Restoration project, funded through
the Illinois Department of Natural
Resources, being conducted by
Scott Robinson, Jeff Brawn, Ed
Heske, and other INHS biologists
to study factors affecting nest
predation on edge-, shrubland-,
and grassland-nesting songbirds.
We tracked radio-collared
raccoons and opossums at night
from two vehicles with antennae
mounted on the roofs. Coordinat-ing
our positions and timing by
CB radio, we recorded simulta-neous
bearings for each animal
several times per night between
about 9 p.m. and 4 a.m. during
three-week tracking sessions in
June and August 1997. Using
a differential global positioning
...two studies
in the Midwest
have impli-cated
the rac-coon
as the
major predator
in agricultural
regions.
Photo by Steve Bailey, INHS Offi ce of the Chief