Saturday, January 3, 2009

A Close Encounter with Ospreys

A group of ten or so "bird banders" had been banding terns on Wainwright Island in late summer of 2008. This particular trip was a “clean up" with the goal of banding stragglers and birds missed on two excursions to Wainwright earlier in the summer. This trip also featured something a little unusual. A Brandt was mixed in with the terns.

Brandt with Terns

The Brandt was a delight to encounter. He/she was a goofy bird that couldn't fly and was taking refuge with the terns. This might have been the highlights of the day, but after we arrived back at the landing on Cedar Island and stowed all of banding gear away most of our crowd quickly dispersed. It was then that John Weske asked to the two of us who remained if we were up for a little different adventure. He suggested that we go back out into the sound to a channel marker where we had observed an Osprey nest with babies and try to band them. John, Rachel Salmon, and I jumped back on the boat and headed out to the nest.

I have always admired ospreys but I had never really looked at one close up. I was a little apprehensive as I maneuvered the boat into the tide flow and John swung onto the marker ladder with a nimble jump from the bow. He was quickly onto the nesting platform. Mom and Dad Osprey were suddenly on the scene screaming and darting through the air toward John.

Ospreys present a banding problem that is different from the problems of banding pelicans and terns as the Osprey babies are asynchronously born. Of a typical clutch of three eggs, they may have been laid -first egg till the last – several days to perhaps even a week or more apart. And, the hatching is spaced out roughly the same, rather than a clutch hatching at (more or less) the same time - as is more usual among birds. So, when we looked into this particular Osprey nest there were three babies. One - the one in the picture below - was closing in on time to fledge. The other two were much smaller, the smallest just a puffball.

Osprey Baby

John grabbed the big chick first and banded it. He wanted to get that bird out of the nest so he could gently handle the little birds as he banded them. I asked John as he handed the big bird down to me after banding it if it would bite. He, of course, told me no. - Note my right index finger where the bird immediately bit me, and notice the size of this beautiful creature's feet with new band.

Rachel Salmon with the biggest Osprey baby

I first become aware of this concept of asynchronous hatching when I read Marie Winn's book Red-Tails in Love? But having this eye to eye encounter made me think about this concept even more. What was the reason for it? What was Mother Nature up to?

A little research led me to find that this asynchronous hatching is seen in various types of raptors, and it is an adaptation to the kind of often wildly fluctuating food supply found in coastal Carolina's rivers, sounds and oceans. During seasons or times of seasons when food is in short supply, the later hatched young will probably starve as the earlier hatched young, being larger and stronger, deprive them of food (siblicide - they push their weaker brothers or sisters out of the nest) And, the size of the brood is reduced to a level in balance with the available food supply. In years of plenty all the young may be able to survive.

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