Ospreys make a comeback in Cook County
Nearly 60 years after pollution forced them to disappear from Illinois, several pairs have made their homes in forest preserves
Forest Preserve wildlife biologists tag a newly hatched chick at John J. Duffy Forest Preserve. (E. Jason Wambsgans, Chicago Tribune / July 11, 2011)
But Chris Anchor, a wildlife biologist with the Forest Preserve District of Cook County, was not deterred. He gently gathered up the large chick and carried it to the ground so it could be tested and tagged.
The birth of this osprey in a southwest suburban forest preserve is part of what is shaping up as a remarkable comeback for the species in Cook County. Ospreys vanished from the state nearly 60 years ago, but eight pairs are successfully nesting in the county and two more pairs are trying, Anchor said. In all, he has counted seven osprey chicks this year.
Widespread environmental pollution in the 1950s and '60s was devastating to the osprey, which survive on fish such as salmon and largemouth bass. Contaminants that killed fish deprived the birds of food, and fish that survived passed toxic substances to the osprey. The insecticide DDT, not banned until 1972, was especially damaging because it thinned eggshells to the point that chicks did not survive.
"DDT was the most limiting factor in the reduction of bald eagle and osprey nesting success," Anchor said. "It took a long time for the DDT levels to drop, primarily in the Great Lakes, and it's taken a good 20 years for this to turn around."
Along with cleaner water, a key factor in the birds' comeback appears to be the nesting platforms Anchor and the Forest Preserve District have erected. The platforms rest atop 40- to 60-foot-tall telephone poles and offer the 360-degree views of the surrounding terrain that nesting ospreys require. "They like to be the highest things around," Anchor said.
According to Field Museum ornithologist Doug Stotz, the osprey disappeared from Illinois in 1952. When they started coming back in the last couple of decades, they appeared first in Cook County, but big trees that made for good nesting sites were sparse.
The birds were also at risk of losing their eggs to scavenging raccoons, which can climb trees, and high winds that blow nests to the ground. The sturdy platforms have given the osprey safer places to start their families.
While there are no reliable estimates of how many ospreys are in the area, Anchor has accounted for at least 27.
"If you look at the population growth curve, you hit an inflection point and the population explodes. That is about to happen now," Anchor said.
Ospreys are a single species of raptor that live near water everywhere in the world but Antarctica. Hovering over water, they swoop down to catch fish using barbs on their feet. With a 5- to 6-foot wingspan, the birds are distinguishable from the similar bald eagle by their light-colored undersides and dark, striated, slightly curved wings.
When ready to nest, a male osprey will find an appropriate site and begin his search for a life partner. If a female approves of him and his site, the couple will produce two to four eggs. A new couple usually raise one chick, while more experienced ones have two or three. Osprey couples living in Illinois spend their winters in warm places like Florida's Gulf Coast and South America, but will return to their nesting sites year after year.
Anchor keeps track of ospreys in the area by regularly visiting the nesting platforms and tagging new birds with radio telemetry tags to monitor their migrations. The data are shared with the U.S. Fish and Wildlife Service.
Ospreys and other large birds of prey are "biomarkers" of the environment, according to Anchor and Stotz, and if things go awry, a drop in their numbers will show it.
"We keep putting all sorts of chemicals in the environment. It's possible one of those is the new DDT, and we just don't know it yet," said Stotz.
In addition to the birds returning to Cook County annually, more birds are migrating to the area from other parts of the country, looking to establish nests, Stotz says.
As the wildlife biologist for all of Cook County, Anchor monitors more than just the osprey, and he hopes the return of the species will help people realize how much wildlife lives in the area.
"You don't have to go far to find an amazing array of conserved plants and animals," Anchor said. "We may live in one of the largest urbanized areas in the country, (but) meanwhile nature's thriving."
Since 1999 the Forest Preserve District has installed 11 nesting platforms, most of them in the southwest suburbs. Two are located on the border between Indiana and Illinois, and two are in the northern part of the county. The public can see one of the osprey nests by visiting the Little Red Schoolhouse Nature Center in Willow Springs.
The newest osprey chick was tagged Monday at Tampier Lake in southwestern Cook County. After collecting the 4- or 5-week-old chick from its nest, Anchor rode the bucket of the cherry picker to the ground with the bird gently clutched to his torso.
District rangers as well as naturalists and volunteers from Sagawau Environmental Learning Center quickly got to work with Anchor to attach a small metal band — the tracking tag — to the chick's right leg.
As the distraught parents circled, the wildlife team fed the baby water with a small pipette. Even before 8 a.m., weather was not on the team's side. The day was sunny, hot and humid, and the chick was at risk of heat stress. Working fast, they turned the 3-pound chick onto its back and drew a blood sample.
"Let's hydrate him one more time, get him out of here," Anchor commanded, and the baby was given water again. With dark storm clouds swirling in the distance, Anchor swiftly returned to the cherry picker and placed the baby back in its nest.
One more osprey thrives in Cook County.