Saturday, November 16, 2013

High wing loads and the diving cormorant

Back in 2008, I spent several hours over the summer at a double-crested cormorant rookery to photograph and observe the birds. In my attempts to photograph them, I immediately learned three things about cormorants; they are terrible at taking off, they fly very, very fast, and their only means of obtaining food is through diving.

I have a very strict rule for photography and that is "know your subject" and use whatever means and resources you have to learn. Of course, time in the field is the best way to learn. When I sat for hours at the rookery photographing, I had lots of opportunities to practice flight shots and learn flight patterns so that I could anticipate some shots. However, I also believe it does not hurt to spend time reading. Through observations and following up these observations with internet and book research on bird physiology and behavior, my bird photography technique has improved. That's not the only reason for my research, I also love physiology and birds just fascinate me to no end.

Most recently, I was reading up on flight dynamics of birds in the The Sibley Guide. From this reading, I had one of those "AHA!" moments, and it was about the cormorant. I finally put 2 and 2 together and realized the connection between the cormorants flight speed and the fact it must dive for food. Here is my best explanation, and that is cormorants have relatively high wing loads.

Wing load is the ratio of the birds body weight to the area of its wings. For a bird, the cormorant is relatively heavy and although its wings can spread 3-4 feet, the wings are not large enough to overcome its heavy body. What this means is that the cormorant performs poorly in flight. Unlike the white pelican that has a relatively low wing load and can therefore soar for periods of time without flapping, the cormorant must overcome its high wing load with great speeds (which provide greater lift) and continuous flapping. It's also interesting to watch them take off and land. A cormorant taking off looks desperate as it violently flaps and uses its webbed feet to push off the water. The landing looks just as desperate as the bird must slow down from very high speeds and do so quickly by using its feet to skid across the water.

There is another reason for the cormorants poor flight abilities and it is the fact that its feathers are easily water-logged, unlike many other birds that have waterproof feathers. It has to do with the fact that the cormorant is a diving bird that captures it's prey in the water, and can dive to depths of 20-25 feet. In this regard, buoyancy is not a good thing, so the heavier body and water-logged feathers provides the cormorant the means to dive efficiently and quickly. This is also why they spend lots of time perched with wings spread out to dry the feathers.

And that's it! High flight speed and terrible take-offs and landings are characteristics of a successful diving bird. So if you want to practice flight shots, challenge yourself and look for the cormorant.


1 comment:

  1. Great insight, thanks! Like the 3rd photo best, unusual perspective.