I walked at dusk down the path in Academy Hills Park towards the tree where Cooper’s Hawks had been raising their chicks since late March. There were no active juveniles cavorting on the limbs. I scanned the nearby trees – no accipiters. I then peered into the branches of the fir tree where the juvies often rested. Again, no activity. It felt strange not to see them.
A few days later, I met Kristin at the nest tree so she could take a GPS reading. “Where do the juveniles roost when they finally leave the nest?” I inquired.
“We don’t really know,” she replied. “At Hawks Aloft we are trying to band as many chicks and adults as possible, hoping it will provide some clue over time.”
I asked when the juveniles know that it is time to leave. She explained that when the parents decide that it is time for them to start hunting for themselves, they just disappear. The juveniles are forced to leave to find food. At first, they hunt in groups, learning from each other.
In a 2004 study conducted by Indiana State University using radio transmitters, only 9.4% of juveniles survived the first winter, compared to 74.5% of adults. They attributed inexperience and risk-taking as the highest causes of mortality among juveniles. Disease might be another cause, since they are at risk of contracting Trichomoniasis from infected prey, e.g. doves and pigeons, particularly young ones.“I am now treating the juvenile from for sub-station nest for Trichomoniasis at Wildlife Rescue,” Kristin reported. “He was brought in by someone who lives across the street from the nest. They found it on the ground in their yard. He was pretty badly infected, but is doing fine.”
It may have originated from prey brought to the nest by its parent, and might explain why there was only one chick visible in the nest. Perhaps the other nestlings contracted it and didn’t survive.
Mourning and White-winged Doves, absent from the area near the nest at Academy Hills, have now returned. One of the neighbors has put up its seed feeder and House Finches and House Sparrows were busily feasting. Life at the park had returned to its normal rhythm.
I am grateful to the tolerance of the two sets of Cooper’s Hawk parents who allowed me to build their nests, incubate their eggs, feed their chicks, bring food to their growing juveniles and finally to allow them to become independent.