Birds: Beaks and Feet

November 11, 2016

Nature Notes by Bill Dunson

 

We enjoy beautiful plants and animals, whether in southwestern Florida or the mountains of Virginia. But how often do we think about the evolutionary values of the peculiar characteristics they possess? Look for special features in each of the birds I photographed within the past three weeks since I returned to Florida.

At Ollies Pond I encountered a purple gallinule walking on lily pads with its amazingly long legs and big feet/toes supporting its weight where no ordinary bird could walk without sinking. The advantage of this specialization is obvious for exploiting this type of habitat, but the disadvantage in other places is also obvious. Its beak on the other hand is short and pointed to pick up small aquatic and amphibious prey.
A large shorebird, the whimbrel, I found alongside a beach lagoon on Palm Island has a strikingly long curved bill for probing in the mud for invertebrates. Its legs are moderately long for wading in shallow water. This is in contrast with the spotted sandpiper, with its much shorter bill and legs. So this would be considered a classic example of dividing the habitat into niches which are exploited differentially by birds with different anatomies.

Herons and egrets generally look similar except that their leg lengths vary and they have behavioral differences in foraging strategy that seem designed to minimize competition among species. This green heron at Kiwanis Park has a very long and pointed bill for catching fish and frogs in fresh water; it tends to stand along the bank or in waterside vegetation. The little blue heron at Lemon Bay Park is slightly larger and moves out into shallow water and stands in aquatic vegetation watching for prey to grab with its long bill. The reddish egret at Palm Island which has caught a shrimp has basically the same general anatomy but is larger and can go into deeper water; it is generally found in salt water and has a fishing technique which is both quite active in pursuit and deceptive by opening its wings to attract fish into the shade provided. The yellow crowned night heron (a juvenile found at Blind Pass beach) has a quite different bill structure which is much more massive for cracking crabs which are its primary food.

Raptors have distinctive bills for tearing and strong talons for holding and killing the prey. We have a pair of great horned owls that serenade us nightly while they fight with the ospreys whose nest (directly over our house) they intend to steal. Other raptors such as this Cooper’s hawk have joined the ospreys in attacking the owls during daytime, but they lack the offensive weapons to do them much harm. The kestrel is our smallest falcon and has a small bill for tearing prey and fairly large talons for its size.

So as you are watching birds, try to note their special characteristics such as beak length and shape, strong talons, leg length and feeding behavior. Think about how these variations make them more successful in competing for survival.

Bill Dunson, Englewood, FL
http://lemonbayconservancy.org/news-blog/nature-notes-by-bill-dunson/i

Bill Dunson

About Bill Dunson

Bill Dunson, born in rural Georgia, skipped 12th grade and went directly to Yale. Bill subsequent-ly received a PhD in Zoology from the University of Michigan, studying softshell turtles. Bill is Professor Emeritus of Pennsylvania State University thanks to a career spent entirely at that institution, teaching and doing research on the physio-logical ecology and ecotoxiciology of reptiles, amphibians and fish. Always curious about nature, Bill has dedicated his life to learning and sharing his knowledge with others. He has served on many advisory boards here in Southwest Florida to preserve the water that gives life to our region.

View all posts by Bill Dunson