Captive Rearing and Release

As an emergency stop-gap measure, one of our first initiatives was to locate wild nests and pull eggs for artificial incubation. This proven technique helps to double the number of young that hatch in a single breeding season. When eggs are pulled, the breeding pair will often lay a second clutch of eggs, while the original eggs and young are reared in our lab.

Eggs are placed in incubators where they will remain until they are ready to hatch. The incubation period for a Puerto Rican Sharp-shinned Hawk is 32 days. Biologists weigh and candle the eggs every day to ensure that the embryos are developing well. Throughout the incubation process, incubators are kept at a specific and steady temperature of 99.4–99.6°F (37.4–37.6°C) and relative humidity is monitored and adjusted as needed to provide the perfect environment for embryo development. The hatching process begins when the eggs are about 30 days old, this is when the chicks begin to crack the egg shell, breathing air for the first time! By 32 days, the chicks will have fully hatched from their shell and are then moved to a heated brooder. 

After hatching, nestlings grow quickly. Within just 3–4 hours of breaking free from the shell, nestlings are able to open their eyes, sit up and beg for food. Biologists watch the young around the clock, feeding them every few hours throughout the day. Each nestling is weighed before and after feedings, this allows the biologists to track the amount of food consumed and to ensure that each nestling is growing and developing properly. A healthy diet and clean environment is extremely important for developing hawks; for the biologists, this means spending a lot of time prepping hawk food and cleaning. To be sure that the nestlings do not become imprinted on humans, they are always raised in sibling groups. As the young grow, they quickly become stronger and true feathers can be seen developing at the wingtips and tail as early as 8 days old. Around 12 days old, the nestlings are able to stand for short periods of time and have begun stretching and flapping their small wings. Within just 20 days of hatching from their shell, young are able to maintain their own body temperature, eat provided food on their own, and are ready to begin the process of being released back into the wild.    

At 20 days of age, young are transported from the Propagation Facility to the release site where they will spend the next seven days acclimating to their new environment and becoming familiar with their surroundings from the safety of the “hack box”. In the wild, young Puerto Rican Sharp-shinned Hawks naturally begin branching from the nest into the tree around 27-30 days of age. This life stage is critical for the development of skills and behaviors that will allow these hawks to survive in the wild which is why we release our hand-reared hawks at just 27 days old. We design releases or “hacking” in a way that allows the hawks to branch, fledge, become independent and disperse as they would naturally in the wild. 

Before the young are released, biologists attach small temporary radio telemetry devices to a few feathers on their back. It is important that biologists keep track of the young hawks for several weeks after being released to ensure that they are roosting in safe locations, away from predators like domestic cats and introduced mongoose. At the hack site, biologists provide food, protection and shelter for the fledglings until they are able to hunt on their own. For most raptor species, the ability to hunt and capture prey is an innate behavior, which means the hawks do not need to learn this ability from a parent. With time and practice, young hawks will naturally begin hunting on their own. When this happens, they are no longer dependent on the biologists’ to provide food and the young hawks will slowly disperse into the forest. For the Puerto Rican Sharp-shinned Hawk, it generally takes about 2–3 months to become independent.