Cool Vibrations

If you’ve walked past or through the Pritzker Family Children’s Zoo this summer you might have noticed the black-crowned night herons nesting high up in the trees. The unique, urban colony is the largest in Illinois, where this migratory species is endangered due to wetland habitat loss.

Have you noticed any of the herons vibrating their necks and wondered what they were doing? Since young herons cannot leave their nests until they fully fledge, they’ve developed a way to cool off while exposed to the hot sun up in their nests. This adaptation helps them avoid hyperthermia (overheating). Similar to dogs and other animals that pant to reduce their body temperature, many heron species vibrate their throats to cool down. This physical mechanism is known as a “gular flitter.”

A black-crowned night heron chick tries to cool off by vibrating its throat, an adaptation known as a "gular flitter.” Photo by Mason Fidino. (Top photo: Two black-crowned night heron chicks share a nest in the colony above the Pritzker Family Children’s Zoo. Photo by Joel Pond.)

By rapidly vibrating the upper throat and the thin floor of the mouth they expose a large, featherless area to moving air. These flapping membranes increase evaporation. Tiny, hot air bubbles float to the surface via blood vessels, and the heat dissipates through the throat. Essentially, body heat radiates up through and out the birds’ throats when they vibrate their necks. Next time you stop by this nesting site on a hot summer day look up for herons vibrating to stay cool!

Scientists with the zoo’s Urban Wildlife Institute have studied this colony and others throughout Lincoln Park for the past seven years, monitoring them daily and helping to minimize disturbances. We keep a close eye on the birds’ health, which also involves collecting fecal samples for scientists at the zoo’s Davee Center for Endocrinology and Epidemiology. Stress-related hormones are extracted from the samples and analyzed to measure changes in the colony’s stress levels over a long period of time.

Mitigating human-wildlife conflict. Providing preventive healthcare for a wild heron colony. These are the kinds of conservation initiatives that will always remain cool.

Maria Jazmin Rios is coordinator of wildlife management for Lincoln Park Zoo's Urban Wildlife Institute.