Jurong Lake - Sunny Side Up

Jurong Lake

West, Singapore

February 2015

One of final finds of the day was this narcissistic Ardea cinerea (Grey Heron) at the edge of the pond sunning.

Sunning, usually a solitary practice, is where birds deliberately expose themselves to sunlight as opposed to merely being out in the sun. Spread-wing postures may serve different purposes in different species. 

Species that spend much of their lives in the open, such as waterfowl and shorebirds, are constantly exposed to the sun. For these species that have little chance for respite from the sun it may be that what we think of as sunning is actually the birds trying to cool down by exposing their feathers.

Some waterbirds have feathers whose structure are not water-repellent, but instead absorb water to decrease buoyancy and facilitate the underwater pursuit of fishes. They also lose body heat tin the underwater chase process. The function of the spread-wing postures in these birds is then to dry the wings, and to thermo-regulate to warm back their bodies. While they will take advantage of full sunlight, these birds need to dry out after every diving session so they are compelled to hang their feathers out to dry regardless of whether the sun is shining.

Cormorants, in contrast, apparently use spread-wing postures only for drying their wings and not for thermo-regulation. They stand with their wings open to keep themselves warm on a cold day and to warm the food in their belly to assist with digestion. The Marabou Storks on cool mornings also turn their backs to the sun and open their wings to warm up. The Black Heron and other birds that feed in shallow water often form umbrellas with their wings. By spreading their wings, they form a shadow so that they can see into the water better. Fish will come to hide in this sheltered "protected" area, and then become easy prey.

Other species spread their wings in the sun to realign their feathers, to force parasites into motion to ease their removal, and to help themselves balance on a perch.

So which one is your reason, Mr Heron?

Sources

"Questions my Grandkids asked me: Why do birds spread their wings when they stand?" (23-Jun-2014) by Johan Smulders from HubPages at http://johansmulders.hubpages.com/hub/Why-do-birds-spread-their-wings-when-they-stand.

"Spread-Wing Postures" (1988) by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye at https://web.stanford.edu/group/stanfordbirds/text/essays/Spread-Wing_Postures.html.

"Sunny Side Up" (06-Mar-2013) by Jill Brown from Australian Birdlife at http://birdlife.org.au/australian-birdlife/detail/sunny-side-up.

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