Friday, December 19, 2014

Nocturnal Creatures (Part I: Pacific Screech-Owls)

Dusk falls quickly in the tropics, and with it comes a rapid transition between the activities of the diurnal and nocturnal fauna.  As darkness falls, the daytime animals take advantage of the last few minutes of fading light.  The last of the day's hummingbirds fill their stomachs with nectar before calling it a night; the howler monkeys bellow one last claim on their territories; and flocks of Tennessee Warbler settle in to roost, nudging and shouldering each other to vie for the best spot on the branch.  Around this time there is a small window, just before the real darkness sets in, in which the bats and owls leave their daytime roosts and begin their nightly routines.  These are the creatures to whom the night belongs.

© Tyler Christensen
Pacific Screech-Owls (Megascops cooperi, above) are perhaps the most common owls in Costa Rica, much like our Eastern Screech-Owls (Megascops asio) at home in New Jersey.  Both species are flexible in their habitats and diets, making them well-suited to thriving in areas with human habitation.  I photographed the owl pictured above on the grounds here at Finca Pura Vida just a few evenings ago.

For the past few nights we have been capturing owls for our research, applying the same method I used during Washington Crossing Audubon Society's Saw-whet Owl Migration Survey.  This method involves the use of several mist nets and an electronic audiolure that plays the male vocalizations of the owl species being targeted.  Ever curious, owls often come in to investigate and wind up in the nets.

© Tyler Christensen
Various research projects require the capture of owls for study.  Ours involves deciphering patterns by which these birds replace their feathers, and whether these patterns can be used to discern the age of a bird in question.  While this research may not be universally interesting (I can think of several people off the bat who were visibly regretful after asking for more detail), I do think we can all appreciate the spectacular encounters that happen to go along with it.

You cannot catch owls here without also catching bats, and catch them we did -- indeed, some were as large as the owls themselves.  Our encounters with these bats will be the topic of Part II of this post.

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