Monday, May 30, 2011

The great white egret

Along side the brown pelican nests are the great white egret nests. This year, I had a difficult time following these guys during my visits. The biggest difference between the pelicans and the egrets is that the egrets have much lower tolerance for intruders. My rookery rule is to get no closer than 50 ft from the edge of the mangroves (for the bird's comfort as well as to get a better shooting angle with a 400mm capacity). With some wind or current, I increase that distance because of the difficulty in getting my boat positioned properly. Staking out and/or anchoring while minimizing my disturbance is a test in patience and sometimes impossible. Today was not so bad and I was able to use the stake out pole (much easier to deal with than the anchor). Inevitably, the white birds become nervous as I approach, while the pelicans appear calm and unwavered. Consequently, I've remained farther away from them and have concentrated on the more accessible pelican nests.

Today however, the egrets were more visible in the nice front light. One reason is that the chicks have grown and are more easily spotted. This imposes yet another challenge and that is to get clean shots of birds that mingle with so many other birds. Nevertheless, I was able to focus on a few egret nests where 1 or 2 chicks lived while the adults flew in and out for feeding and other chick caring responsibilities.

Watching an adult egret feed its young is fascinating but not easy. The pelican feeding is quite unruly, but what makes the egret feeding so much more painful to watch is that the birds have very sharp beaks. This cannot be a pleasant experience for any involved. The adult must avoid getting a chick beak in its eye and in fact, I noticed one adult that appeared to have an injury possibly from an impalement. In the meantime, with 2 or more chicks fighting for food, they must also avoid getting impaled. From my observations, the chick clamps its beak onto the adult's beak, unlike the cormorant and pelican chick that is allowed to put its entire head and neck inside the adult's throat. For obvious reasons, the sharp beaked egret cannot let that happen.

The feeding ritual goes something like this. The adult flies in while the chicks jab vigorously at the sky. The adult stands tall for several seconds while the chicks stretch upward attempting to get to the adult's mouth. After a short time, one of the chicks manages to clamp onto the adult's beak and without warning, the adult bends down as each of the chicks attempts to get the regurgitated food out of its mouth. This lasts for several seconds and then the adult stands tall again. It stretches its long neck and points its beak straight up and holds this position for a minute or so. Then, the feeding begins again. I am guessing that the adult is doing this stretch to move the regurgitated food back up into its mouth.

After feeding, the adult manages to get away and looks relieved when doing so. After one chick was fed, I focused on it as it flapped its wings, obviously irritated that the parent had left it again. With these egret scenes, I went back and forth between horizontal and vertical shots. While focusing on this one young chick, I held the camera horizontally in attempt to capture its wings. What I realized afterwards is that a vertical shot would have rendered a much better shot. Case in point, look at the first photo below. A vertical frame would clearly have captured the wings in their entirety. Once again, I missed my shot. The next one is not bad and I was glad to have captured the scene with the right exposure and sharpness.

Like the pelican, survival rate among GWE chicks is as low as 25% during the first year of life. While the pelican chicks require 4-5 mon before reaching independence, the GWE chicks are on their own in 2-3 mon. Chick competition in the nest is fierce. The adult lays its first egg and will continue laying up to 6 eggs with 2-3 days between each egg laying. This is amazing to me because chick growth is fast and in theory (my theory) the preceding chicks could outsize the new chicks substantially. However, whenever I observe a GWE brood, the 2 or 3 surviving chicks appear similar in size. In contrast, the 2 or 3 pelican chicks within a brood vary noticeably in size despite only hours between hatches. The GWE lays about twice as many eggs as the pelican. My theory is that competition among the egret chicks is so great during the initial period that less than half survive, resulting in 1 to 3 strong chicks to continue growing. The smaller and weaker pelican may be able to hold on longer and continue growing for some time, possibly surviving the long haul. Growth of the GWE chick is so fast that they often look as large as the adults. Notice the similar size of the adult and chick in the first photo below.

Enjoy these photos of the absolutely great white eget.

No comments:

Post a Comment