The Pennsylvania Bird Atlas engages birders to canvas the commonwealth


A keen observer can sometimes hear a “boom” over the row houses on summer evenings in Philadelphia. The sound marks a male common nighthawk defending his territory, flexing his wings as he dives. The insect-eating birds nest on flat, gravelly surfaces. These can be bare patches of ground in a forest, but they can also be city roofs.

Unfortunately, it turns out the common nighthawk is becoming less and less common. Since the 1960s their numbers have been dropping a little bit every year, adding up to a population decline of about half. It could be that modern insecticides have left the birds with fewer bugs to catch, or it could be that nesting spots are disappearing. It will take more data to understand what’s happening to nighthawks, and much of that will come from birders.

Birders, unlike the nighthawk, are growing more common. About 45 million people watch birds for fun, according to U.S. Fish and Wildlife Service survey data. Birders produce a lot of observations that are useful to scientists and conservation agencies, but they aren’t perfect. We head outdoors with our binoculars to visit places where we can reliably find interesting birds rather than spend scarce free time on spots that no one else has vouched for; it is in the individual birder’s interest to go where other birders have already proven the trip is worthwhile. The collective effect, though, is a patchy map of observations with lots of places left un-birded.

For scientists looking for a comprehensive picture of how birds are doing across Pennsylvania, this can present a problem. The Third Pennsylvania Bird Atlas (PBA3), which kicked off at the beginning of the year, aims to solve it.

“An atlas is a collection of maps,” says Amber Wiewel, the biologist coordinating PBA3. “When talking about a bird atlas, it is a collection of maps of where birds are distributed in a period of time.”

The atlas, run by Hawk Mountain Sanctuary (in the mountains about 85 miles northwest of Philly) in collaboration with the Pennsylvania Game Commission, is a five-year effort to comprehensively document the commonwealth’s birds.

Pennsylvania is the fifth-most birded state in the country, based on the numbers of checklists submitted through eBird, the online portal that has become the default community science medium for logging bird observations. But those observations are clustered where the most people live, and beyond that, by the habits of birders. “We’re really biased in how we bird and when and where we bird,” Wiewel says.

The atlas aims to spread birders across the landscape by dividing Pennsylvania into 4,938 blocks, each about three miles square. County-based atlas organizers can make sure no corner of the state goes un-birded by ensuring that every block gets at least a minimum level effort. If observations are clustered too much — like in a block with a popular park — they can ask volunteers to try spots in other blocks.

This project is for everybody, all levels. It’s not just really expert birders. If you just started birding you can contribute.”

— Manny Dominguez, Philadelphia birder

Previous bird atlases, conducted in the 1980s and early 2000s, made heavy use of paper forms that birders filled out based on their observations. Today, eBird makes it a lot easier for birders to record data and for organizers to process and analyze it.

The organizers have broken the project into three layers. The breeding bird atlas will take observations for just over five years, from 2024 to the end of February 2029. A winter atlas will run from December through February each year, covering the under-birded season. Last, professional observers and experienced volunteers will do point counts, in which they stay put at assigned locations for a standard period of time and document every bird they see and hear.

The second bird atlas, conducted by the Carnegie Museum of Natural History with the Game Commission in the early 2000s, found that some species like bald eagles and peregrine falcons had expanded their ranges in Pennsylvania, while others such as the common nighthawk had declined.

Getting an accurate collection of maps is critical, as bird populations across the continent have taken a beating. An alliance of bird conservation organizations announced in 2019 that the breeding population of birds (populations fluctuate seasonally as babies are born and raised and as they migrate, so breeding birds serve as a stable population indicator) in North America had fallen by 3 billion. Habitat destruction, invasive species such as house cats, and collisions with windows have taken their toll. Climate change is already starting to complicate everything: warmer temperatures and changes in precipitation mean some habitats, such as cool mountain forests, are shrinking and may disappear entirely. As the timing of spring and fall change, migrating birds may show up too early or too late to take advantage of seasonal food sources they rely on.

Volunteer birders will play a major role in documenting the commonwealth’s bird life. Manny Dominguez and Tanya Burnett, avid birders with day jobs, are coordinating volunteer atlas efforts in Philadelphia. Dominguez started birding during the pandemic. Soon he was going on every guided birding walk he could find. “It kind of snowballed. I have to bird every day.”

Dominguez says not everyone has to be as committed a birder as he is to take part in the atlas. “This project is for everybody, all levels. It’s not just really expert birders. If you just started birding you can contribute, and all your data can be used for good purposes, like tracking the trends of certain birds that breed in Philly.” Birds like the common nighthawk.

Manny Dominguez is a volunteer coordinator for the Third Pennsylvania Bird Atlas. Photo by Troy Bynum.

Learn more about how to take part in the Pennsylvania Bird Atlas at ebird.org/atlaspa


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