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Maintaining
Water Levels Helps Calumet-area Night Herons
Oh,
the trials and tribulations of a heron rookery! The Calumet
(southeast Chicago) black-crowned night heron nesting colony
has had its ups and downs with highly changeable water levels
in the marshes. Excessively high water levels flood out
and eventually kill the emergent vegetation that the night
herons nest in. Fortunately, the city of Chicago is now
taking an active role in regulating water levels so that
nesting black-crowns will flourish in the Calumet area.
Over
the past two years, the Calumet night herons have nested
exclusively at Indian Ridge Marsh, an area gradually being
flooded out because of a blocked drainage culvert. With
the high water, the marsh vegetation receded, resulting
in a 10-year low count of 559 adult night herons surveyed
on a May 2000 census (compared with 808 adults in 1999,
and 712 in 1998). In February 2001, the Chicago Department
of Environment (in cooperation with various other agencies)
came to the rescue, clearing out the blocked drainage culvert
at Indian Ridge and then installing a permanent water level
control mechanism a month later. Then, however, the water
levels dropped too quickly. By late March, water levels
at Indian Ridge were far too low to provide the cover night
herons need to nest successfully.
The
water drainage has since been stopped, and water levels
have continued to rise from the spring rains. In the meantime,
the Calumet night herons have opted to relocate to an alternate,
adjacent wetland. A May 2001 survey revealed 706 adult black-crowns
present — well up from the number last year. An important
component of night heron management is allowing for the
availability of alternate nesting sites should the primary
site be rendered unsuitable. — Walter Marcisz
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