As the sun sets, the first stars begin to twinkle in a deep blue sky. A male Flammulated Owl gently calls “who-who-hooo…”, and is answered by a female tucked snuggly into a cavity. Her mate flies to the aspen, his movements silent, a crippled moth in his beak. At the sound of his mate’s incessant begging, he flies into the cavity. Suddenly, a net covers the cavity entrance and the male owl flushes straight into it. Two grinning college students stand below, waiting with a ruler and blood sampling needle in hand. Thus begins the quiet, peaceful night.
Dr. Brian Linkhart’s 30 year study on Flammulated Owls has revealed hitherto unknown aspects of the life history, reproductive habits, and survival of the species. A subject I found particularly interesting this week concerns dispersal during the nesting season. What happens to fledgling Flams (that’s slang for Flammulated Owl) in the years to follow? Flammulated Owls exhibit low philopatry and far-flung natal dispersal. Phylopatry is the tendency of a species to return to the territory in which they were born. There is obviously an evolutionary advantage in choosing to disperse far from the birthplace: reduction of inbreeding. Breeding far from the home forest generates genetic diversity. This week, we captured a male that fledged from a nearby territory in a previous season. Such cases are rare. When they do occur, the opportunity to study at which age males become territorial and start breeding arises. Only five birds have been caught returning near the study site in which they were born. Because they were banded, Linkhart knew their ages to be 7, 6, 5, and 2 years old.
Male Flammulated Owls are extremely faithful to their territories, even when a better territory (one with better habitat, roosts, and food) opens up near them. Females are less so. They often flip-flop between nearby territories and exchange mates, sometimes based on how productive a previous year’s nesting proves, but also sometimes for no apparent reason. This is why capturing females becomes critical during the incubation period. During this period, they exit the cavity for a brief period at dusk and are most easily captured then. After capture, we can read the band and know which territory they nested in previously or if the female is returning to the same territory (and most likely the same mate). Unbanded females are not uncommon.
I experienced my first successful attempt capturing a female at a cavity this week. But my unsuccessful attempt is the better story to tell. I had been holding the net over the cavity for about 40 minutes and the blood had rushed down my hands, they began to feel tingly. My neck hurt from staring upwards, waiting for the female to poke her beady-eyed head out of the cavity. And I’ll be right here when you flush, ready to catch you, I thought. The male came around and hooted, trying to call her out of the cavity. Finally, she flew out with a burst and hit the net. I began to lower the pole as she flopped about. But then I heard the rush of wings and my heart skipped a beat as I watched her fly through a hole in the bottom of the net. I had repaired the very same net earlier in the afternoon. I thought I found all the holes, but she managed to slip through a tiny opening.
I quickly peeped the cavity and found three white, ping-pong ball shaped eggs. The evolutionary story behind their elliptical shapes makes perfect sense. Birds that nest on cliffs or in trees lay eggs that come to a point at one end, which is more pronounced in some species than others. For example, ledge-nesting murres lay pyriform, or pear-shaped, eggs. Any motion and the egg rolls itself in a circle. Their eggs are less likely to drop into the sea or plummet over rocky cliff edges. Cavity nesters can dispense with such worries all together and thus their eggs look like perfect circles. After viewing the eggs I lowered the pole as soon as possible to allow the female to return and incubate in peace.
And so ends another exciting week among owls….