Yellow-crowned Night Herons Adjust to Changing Climate
link to photos and graph -
http://www.ccbbirds.org/2015/05/18/yellow-crowned-night-herons-adjust-to-changing-climate/
By Bryan Watts
Over a span of only 50 years, the yellow-crowned night heron has shifted its
breeding season by more than 20 days. A comparison between incubation dates
collected in 2015 and dates collected decades earlier (1960-1969) reveals the
shift in season. Birds are both arriving on the breeding grounds and laying
their eggs earlier in the Tidewater region of Virginia.
Along the Atlantic Coast, the life of a yellow-crowned night heron is spent in
pursuit of one thing: fiddler crabs. Their hunting times are scheduled around
low tide when the crabs are accessible. They stalk fiddlers in the salt marsh
and run them down on the mud flats. Females gorge on fiddlers to produce eggs,
and breeding pairs feed the crabs to their young. Arrival of the herons on
breeding grounds is timed exactly to when the crabs emerge from their burrows
for the spring, and the herons' departure in the fall is timed to when the
crabs return to their burrows for the winter.
Activity in fiddler crabs is very sensitive to temperature. When the
temperature rises above 15°C (59°F), they emerge from their burrows and become
active. Crabs retreat to their burrows and move underground when the
temperature drops below 15°C. The date in spring when temperature passes the
15°C threshold is advancing, extending the season of fiddler availability.
Yellow-crowns appear to be adjusting to the shift in season.
The 2015 season is the first of a multi-year study to compare the breeding
ecology of the yellow-crowned night heron to a study conducted within the same
colonies in the 1960s. The ten-year dataset from the 1960s was collected by
Constance DuPont Darden. Mrs. Darden (former first lady of Virginia) was
passionate about yellow-crowns, and her information has contributed a great
deal to our understanding of the species. Her dataset is housed within The
Center for Conservation Biology.
Climate change is a change in the statistical properties of the climate system
over long periods of time. Regardless of the underlying causes of this change,
the earth has been experiencing a documented shift in climate for decades. How
wild species respond to changes in climate will determine many aspects of their
ecology including their geographic distribution, the timing of significant
events in their annual cycle and for some their survival. Understanding the
implications of these shifts is a growing focus of conservation biology.
Because of both their migratory status and specialized diet yellow-crowned
night herons represent a model system for investigating how species respond to
a changing climate.
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Michael Wilson
Center for Conservation Biology
College of William and Mary & Virginia Commonwealth University
P.O. Box 8795
Williamsburg, VA 23187-8795
phone: 757-221-1649
fax: 757-221-1650
email: mdwils@xxxxxx
web: www.ccbbirds.org
