The Bald eagle, our National Symbol, occurs throughout the United States, Canada, and northern Mexico. Bald eagles are present year-round throughout Texas as spring and fall migrants, breeders, or winter residents. The bald eagle population in Texas is divided into two populations; breeding birds and non-breeding or wintering birds. Breeding populations occur primarily in the eastern half of the state and along coastal counties from Rockport to Houston. Non-breeding or wintering populations are located primarily in the Panhandle, Central, and East Texas, and in other areas of suitable habitat throughout the state.
The bald eagle is one of nature’s most impressive birds of prey. Males generally measure 3 feet from head to tail, weigh 7 to 10 pounds, and have a wingspan of 6 to 7 feet. Females are larger, some reaching 14 pounds with a wingspan of up to 8 feet. Adults have a white head, neck, and tail and a large yellow bill.
Bald eagles are opportunistic predators. They feed primarily on fish, but also eat a variety of waterfowl and other birds, small mammals, and turtles, when these foods are readily available. Carrion is also common in the diet, particularly in younger birds. Bottom-dwelling fish tend to occur more frequently in the diet. It is thought that the downward visual orientation of bottom-feeding fish makes them more vulnerable to eagle attacks than surface sight-feeders, which are more aware of movements from above. Eagles capture fish by extending their talons a few inches below the water’s surface. Therefore, live fish are vulnerable only when near the surface or in shallows. Studies in Texas have shown that eagles commonly eat coots, catfish, rough fish, and soft-shell turtles.
In Texas, bald eagles nest from October to July. Nests are constructed primarily by the female, with the male assisting. The typical nest is constructed of large sticks, with softer materials such as leaves, grass, and Spanish moss used as nest lining. Nests are typically used for a number of years, with the birds adding nest material every year. Bald eagle nests are often very large, measuring up to 6 feet in width and weighing hundreds of pounds. Eagles often have one or more alternative nests within their territories.
Peak egg-laying occurs in December, with hatching primarily in January. The female lays a clutch of 1 to 3 eggs, but the usual clutch is 2 eggs. A second clutch may be laid if the first is lost. Incubation begins when the first egg is laid and usually lasts 34 to 36 days. The young generally fledge (fly from the nest) in 11 to 12 weeks, but the adults continue to feed them for another 4 to 6 weeks while they learn to hunt.
Nest surveys in Texas from 1981-2003 have shown that greater than 80% of the active nesting territories successfully produced young, with production averaging greater than 1 young per active nest found. Studies show that at least 70% of the juveniles survive their first year. Bald eagles reach sexual maturity at 4 to 6 years of age; however, they have been known to successfully breed at 3 years. They are monogamous and are believed to mate for life; however, if one of the pair dies, the surviving bird will accept another mate. Bald eagles are believed to live up to 30 years or more in the wild.
Winter and early spring are enlivened by some twenty-five American bald eagles that migrate to the Texas Hill Country for the winter. Seeing these national symbols soaring through a crisp cloudless blue sky is a sight no one will ever forget. Nine miles east of Llano on Hwy 29 a family of bald eagles can be viewed from the roadside during the nesting season. The Vanishing Texas River Cruise is a prime ecological trip departing from Lake Buchanan. The cruises provide spectacular views of the lake, the Colorado River, native Texas wildlife, waterfalls, world-class bird watching and wintering bald eagles.
Jess Thompson is a photographer who has been documenting these Bald Eagles for many years. He and his wife, Peggy, own Cottonwood Photography in Burnet. They have published a book of photographs that follows the bald eagles through the nesting season. You can see their pictorial history of the birds posted on their Web site, cotton woodphotography.com. San Saba Bird and Nature Club will be hosting a program given by the Thompsons on November 16, 2010, at the San Saba Civic Center at 7pm. Everyone is invited.