With New Jersey's osprey population continuing to grow, state officials are turning to citizen observers and private groups for help monitoring a species considered an important indicator of environmental health.

Researchers estimate there were 567 nesting pairs of ospreys in the state this year, according to a report released this week by the New Jersey Division of Fish and Wildlife and a private nonprofit organization, Conserve Wildlife Foundation of New Jersey. The report was based on ground surveys conducted by staff and volunteers in June and July.

Based on the data collected in those surveys, researchers believe the population is continuing to grow, with about two young osprey born per nest, twice the minimum needed to maintain a stable population.

"The results from this year were really positive for ospreys. You can never complain when you're about twice the minimum productivity needed, so we can expect the population to keep growing," said Kathleen Clark, the biologist at the Division of Fish and Wildlife who helped lead the osprey survey project.

That's a vast improvement over 1973, when destruction of habitat and use of DDT-based insecticides reduced the state's osprey population to just 53 pairs. The next year, New Jersey listed the "fish hawks" as endangered.

Conservation efforts and a ban on DDT saw a boom in the osprey population, with the birds upgraded to "threatened" status in 1985. The next time ospreys are up for a bird status review, they will likely be upgraded again, Clark said, based on the growth in the population.

With a diet that consists almost entirely of fish, ospreys are important as indicators of environmental health, Clark said. The fact that their numbers have rebounded suggests an abundance of healthy fish and robust aquatic systems, she said.

Ospreys also thrive in a variety of areas, making them useful for comparing the health of, say, the Atlantic Coast vs. the Delaware Bay. The osprey population on the coast grew rapidly in the 1980s and '90s, Clark said, while the bay population struggled to recover, reflecting higher toxin levels in the Delaware Bay.

As ospreys move away from being an endangered icon of environmentalism, Clark said, the state will shift its focus off the birds, making citizen participation more important.

"When I started in my career 30 years ago, ospreys were one of our focal species," she said, describing efforts to increase the number of large nesting platforms that have been built across the region. "Once they looked like they were getting stable, we were pulling back our effort on it."

This year, project members placed red bands on young ospreys, a new initiative to encourage citizen observation. In addition to the traditional bands used by scientists to track bird migration and age, the new bands will allow photographers and observers to go online to report a red-banded osprey.

Citizen observations will allow scientists to monitor bird sightings and learn more about foraging habits, migration routes, and life span.

Plus, Clark said, ospreys are generally tolerant of human observation, making them a useful way to connect the public with environmental research.

"It also helps us tell stories about the ospreys . . . where this bird came from, where it was going," she said. "When people can connect to some of those individual stories and really understand how far those birds are flying every year, it helps people gain an appreciation for wild animals and how they make their living."

jlai@phillynews.com

856-779-3220 @elaijuh