One of the most easily recognized and photogenic birds in America can be seen every day of the year at Hagerman. The largest member of the heron family, the great blue heron stands four feet tall and has a six foot wingspan. The name is misleading. Rather than blue it is largely gray with a long yellow-orange bill, yellow eyes, long pale legs and black occipital patches separated by a white stripe. The underside of the neck is white with black and brown hatching.
The great blue is solitary most of the time except when roosting or breeding. Its diet is mainly fish, frogs, snakes and other marine life. While foraging it slowly stalks its prey. It may remain motionless for minutes before suddenly striking with its long uncoiled neck. Small fish are grasped in the bill and large ones are impaled. They are then tossed in the air and swallowed headfirst. Great blues tuck their heads close to their chest in flight, making them easy to identify.
As the days lengthen early in the year light penetrates the skull stimulating hormone production. This initiates migration and breeding. In the south some birds do not migrate. Hormonal changes produce remarkable physical changes. The most obvious marker is a bright electric blue skin patch between the eye and bill in a location called the lores. The legs become salmon colored and tha crown feathers are elongated. The male is about ten percent larger than the female. Otherwise both sexes appear identical. Courtship is initiated by the male who finds an old nest or builds a new one and stands by it engaging in a series of stretches called displays. His new mate will reciprocate with displays signalling her acceptance of his overtures. She then proceeds to rebuild the nest to her specifications with his help. When this chore is completed more mutual displaying occurs followed by copulation. The clutch usually consists of four eggs. The eggs are hatched after four weeks of incubation.
Both parents share the responsibilities of incubating, catching food and feeding the chicks by regurgitating partially digested fish. As the chicks mature the competion for food becomes violent. The youngest and therefore the weakest chicks often die from starvation or fratricide. By eight weeks when the chicks are almost as big as their parents and ready to fledge. By the end of the first year less than half will have survived.
The greatest concern for the future of all birds is the unremitting habitat destruction due the explosive human population growth. The world’s population in 1930 was two billion. By 2011 it was up to seven billion with a projection of nine billion in 2030. The ramifications of these changes should be obvious.
Text and photo by Phil McGuire
For more information about Hagerman National Wildlife Refuge, see the official site, http://www.fws.gov/southwest/refuges/texas/hagerman/index.html and for information about the Friends, see http://www.friendsofhagerman.com.