Illinois Natural History Survey Reports

              R e p o r t s
Winter 2007
No. 390
Bluegill as Homebod-ies:
Do Males Display
Fidelity to Nesting
Sites?
2
Contaminants in Tree
Swallows
3
The Tree of Life Web
Project
4
Species Spotlight:
Prairie Trout Lily
6
The Naturalist's
Apprentice: The
Anatomy of a Plant
7
Continued on back page
INSIDE The Black-crowned Night-Herons of Lake
Calumet Part I: Population Trends and
Nesting Ecology
Black-crowned Night-Herons
(Nycticorax nycticorax) are
small, stocky herons which,
as their name suggests,
are most active during the
late evening through early
morning hours. They forage
in a variety of aquatic
habitats, feeding primarily
on small fish and crayfish.
Although Black-crowned
Night-Heron (BCNHeron)
populations have increased
nationwide since the banning
of DDT, Illinois has not
enjoyed this recovery. The
decline of the colonial-nesting
BCNHeron as a breeding
species in the state of Illinois
has been documented
by a number of authors.
One of the largest remaining
breeding colonies of this state-endangered
species in Illinois
nests in marshes adjacent to Lake
Calumet in the south Chicago
area. The Calumet region of
southwestern Lake Michigan
was once a vast complex of
glacial lakes, wetlands, and sand
prairies. This region is now one
of the most heavily industrialized
in the U.S., and has been greatly
impacted by industrial activities,
waste disposal and discharge,
urbanization, and changes
to surface and groundwater
hydrology. In spite of extensive
habitat loss and degradation, the
area remains among the most
biologically diverse in the state
of Illinois. Consequently, key
ecological features of the region
are being rehabilitated, managed,
and preserved according to the
Calumet Ecological Management
Strategy, the framework for the
Calumet Open Space Reserve.
The BCNHeron, a key species of
conservation concern, annually
nests in the area.
Young-of-the-year BCN-Herons
were reported in the
Calumet area as early as 1874.
Throughout much of the early
part of the 20th Century the Lake
Calumet BCNHeron colony
was located along the Calumet
River just north of the confluence
with the Grand Calumet River.
The BCNHerons have nested
at wetlands adjacent to Lake
Calumet since the Thomas J.
O’Brien Lock and Dam went into
operation in the late 1960s. The
number of BCNHerons nesting
at these wetlands has fluctuated
widely over the last two decades.
The peak breeding population
at Lake Calumet wetlands has
varied, from a high of nearly
1,600 in 1992 to less than 600
in 2000. Although there was a
declining population trend during
much of the 1990s, numbers have
been more or less stable at 600
to 800 breeding herons in recent
years.
Most BCNHerons begin
arriving at the Lake Calumet
wetlands during the third week
of March. Males soon begin
nest building and displaying
in an attempt to attract a mate.
During the two years of this study