Bald eagles (Haliaeetus leucocephalus) are known for building the largest tree nests ever recorded for any animal species. Not surprisingly, these homes are very large in order to compensate for the size of the parents and their fast-growing young. By the time eagle chicks are 9 weeks old, they are fully grown. These young reportedly remain in the nest to gain strength for 10 to 12 weeks before flying off.
While in those nests, sibling rivalry can get quite competitive as chicks turn into fledglings. Unfortunately, domination can occur when the older eaglet acts aggressively to its younger and smaller brother(s) or sister(s). Sometimes, the nest gets a little small come feeding time.
At CROW, a fledgling bald eagle was admitted to the hospital from Fort Myers. The eagle had been observed on the ground without care from its parents for more than 24 hours before it was rescued.
“The nest was easily visible by people that lived in neighboring houses. It is not uncommon for fledgling eaglets to end up on the ground when they are learning to fly, but they should not stay on the ground for an extended period of time,” said Dr. Robin Bast, CROW veterinary intern.
“The parents were observed in the area interacting with the eaglet; however, there were two other siblings still in the nest and this means competition for resources as well as space in the nest.” When the fledgling arrived at the hospital, the intake exam did not reveal any broken bones or injuries. The eagle’s body condition score was low, indicating it was thin. Blood samples were tested and revealed the bird was also anemic.
Dr. Bast confirmed no orthopedic abnormalities were noted. “The fledgling was thin and mildly dehydrated, and as a result had a mild anemia – low red blood cell count. It was treated supportively with an injection of iron and vitamin B12, and subcutaneous fluid therapy upon admission to the hospital,” she said. “The next morning, it was moved to an outdoor enclosure and ate readily. It was likely thin because of competition for resources with two other siblings in the nest.
“Bloodwork was repeated five days after intake, and was within normal limits (thus) anemia resolved. At that time, the eagle’s weight and body condition had improved with nutritional support.” Since there were two other eaglets in the patient’s nest, CROW veterinarians decided it was best to release the patient once it was fully flighted rather than re-nest it immediately as it may be pushed right back out of the nest by the siblings.
Dr. Bast stated that the patient continued its clinic stay in a large flight enclosure and practiced making strong short flights on its own. Siblicide, or death resulting from competition for resources among siblings, is not an uncommon occurrence with eagles, she said.
After its second week at CROW, the bald eagle was released near its nest. “This fledgling was successfully reunited with its family at the nest site on May 12, after two weeks in hospital,” said Dr. Bast. “Both parents and both siblings were observed in the nest at the time of release and the next day the eaglet was observed in the nest tree with its siblings.”
CROW Case of the Week stories are written by Bob Petcher and appear weekly in the Island Sun and River Weekly Newspapers.