To Protect Broad-winged Hawks, We First Need to Know Where They Migrate

Located in the quiet southwestern corner of New Hampshire is the Monadnock Region, whose namesake, Mount Monadnock, commands the landscape at a locally impressive 3,165 feet. For the people that call this area home, the Broad-winged Hawk might be the Monadnock Region's unofficial avian mascot. Each fall, thousands of nature enthusiasts visit this region to witness the impressive kettles of migrating hawks from near the summit of the smaller Pack Monadnock at the Pack Monadnock Raptor Observatory.  

Despite their local celebrity and ubiquitous nature, the Broad-winged Hawks of the Monadnock Region and New England remain a relative mystery. Researchers know very little about their ecology, especially their migrations. But, all that is about to change thanks to a new tracking study led by two of North America’s dedicated raptor researchers, Dr. Laurie Goodrich and Dr. Rebecca McCabe, and an on-the-ground partnership between the Broad-winged Hawk Project of Hawk Mountain Sanctuary in Pennsylvania and the Monadnock Region’s Harris Center for Conservation Education. 

For Goodrich, the impetus for the Broad-winged Hawk Project is simple: There are warning signs of a population decline. “The Broad-winged Hawk is the most commonly sighted migrant at hawkwatches in eastern North America. However, we are starting to see significant declines at a subset of hawkwatches, particularly in the eastern part of their range.” Goodrich adds, “It also showed a diminished nesting range in Pennsylvania.” This news is something that hits close to home for her, who, as Hawk Mountain’s director of conservation science, has a storied career studying raptors around Pennsylvania and beyond.  

The tracking of individual hawks from their breeding grounds is at the center of the Broad-winged Hawk Project’s conservation research. According to Goodrich, “We launched our tracking study to try to understand their year-round ecology and what conservation threats they might face in their nesting, wintering, and migration periods. She then explains, “From 2014 to 2019, we tracked Broad-winged Hawks nesting in Pennsylvania and compared their migration ecology to three birds from Alberta tagged by the Migratory Connectivity Project.” During those earlier tracking studies, two of the Alberta-nesting hawks wintered in northeastern South America, a completely different wintering area than the Pennsylvania individuals, revealing to Goodrich and others insight into the migratory connectivity of these birds, that is the geographic and annual links between individuals and populations within a species.  

Arriving at the Monadnock Region in late June 2021 during the peak of New Hampshire’s Broad-winged Hawk nesting season, Goodrich and McCabe set out to deploy transmitters on several individual Broad-winged Hawks to further unravel the migration mysteries of these small woodland raptors. “We wanted to tag birds in New England to understand if they show different wintering areas, migration dynamics, or timing.” If they do, according to Goodrich, “It is crucial to understand as different populations can be subject to different conservation pressures.” 

After three days of trapping during the hot and steamy conditions of late June at the Harris Center’s Super Sanctuary, Goodrich, McCabe, and a group of volunteers reached their goal of successfully outfitting three Broad-winged Hawks with tracking devices, a first in the history of studying individuals of this species from this region. Among the birds equipped with a transmitter were a male and female (dubbed “Harris” and “Monadnock”), each outfitted with Microwave Telemetry, Inc. satellite tags, and a single female (“Thelma”) who received a newly designed GPS-GSM cellular transmitter from Cellular Tracking Technologies.  

For McCabe, these newly designed GPS-GSM cellular transmitters are extremely exciting. “I am really pleased with the design of the unit and how it sits slightly raised on the bird’s back.” As with any tracking technology, there are conditions under which they perform best, and many of the transmitters deployed still do much better in open habitats than in the closed canopies of forests. In a frustrating routine of “Can you hear me now?”, the trees that make up the preferred habitat of Broad-winged Hawks can sometimes block the logger’s ability to transmit data while also shading the transmitters solar-panels. To solve this challenge, these tags have some unique features. “These units are designed to reduce feather coverage and have an internal GSM antenna which allows the location data being collected to transmit to cell towers along the bird’s migratory pathway,” says McCabe. “If the bird travels outside of cell tower range for a period, the data is stored, and once it travels back within range, the stored data is transmitted.”   

An exciting feature of the new device is its GPS-quality level precision in mapping exactly where on Earth a tracked bird is in time and space. For these tags, the level of error is only three meters. This spatial resolution is a massive improvement from other satellite tags, whose precision often ranges between 500 and 1500 meters.  

For Goodrich and McCabe, the deployment of tags is only the beginning of the actual research, and a tracking study goes long beyond the initial moments spent deep in mature forests, where nurturing Broad-winged Hawk parents pierce the air in alarm whistles from nearby nests. As with any of these studies, there is a period of holding one's breath, awaiting the data to arrive. Thankfully, researchers must wait less and less for that to occur.  

Monadnock, the female banded by Goodrich and McCabe, flew northwest from New Hampshire into Vermont in a series of flights outside of her breeding territory, reaching just south of the US-Canada border by the end of August 2021. While these flights are seemingly in the opposite direction of what most of us might expect during the fall, Goodrich notes that they have seen pre-migration movements to the north and west in about 30 percent of tracked individuals. While that is not new, McCabe adds, “Monadnock’s initial flight to the northwest is unique in the distance covered and is possibly the longest such flight that we have recorded.” 

After a week spent in Vermont, Monadnock started migrating south on September 8th along with Thelma, and Harris following suit ten days later. By September 25th, Harris took the lead flying through Georgia and Alabama while Monadnock and Thelma passed through Kentucky and Tennessee. Twelve days and 1,460 miles later, Harris and Thelma cruised past the infamous “Rivers of Raptors” watchsite in Veracruz, Mexico alongside 65,972 other Broad-winged Hawks that day. Harris reached his wintering grounds near Barracon in Colombia on October 25th as Monadnock trailed behind. On November 6th, Monadnock settled down near Villars, Colombia approximately 118 miles southeast of Harris’s wintering site. Due to the configuration of the GPS-GSM units, the one Thelma’s sporting, the last location for Thelma is from October 14th in Honduras. Goodrich and McCabe hope to hear from Thelma and the other GPS-GSM- tagged birds soon.  

In the end, the data gleaned from transmitters such as the ones deployed in New Hampshire will help researchers like Goodrich and McCabe understand where these birds migrate and inform management and conservation decisions throughout the Western Hemisphere. However, data gaps remain in the tracking of Broad-winged Hawks, and there is still much to uncover. McCabe notes, “In addition to identifying other migratory corridors and wintering areas, we are interested in characterizing stopover habitats and determining if there are key stopovers or stopover habitats along Broad-winged Hawk migratory routes.” She adds, “With the entire population of Broad-winged Hawks migrating between North and South America, stopovers are critical areas for resting and refueling. If one Broad-winged Hawk is using a stopover year after year, many others are likely doing the same.” 

For Goodrich, impressed by the number of nesting Broad-winged Hawks around southwestern New Hampshire, there is a desire for conducting future tracking studies out of the Granite State, and to follow up with nests and tagged birds from their research efforts in 2021. She also notes that while early tracking studies targeted adult females, which tend to be a little larger and therefore better fit for tracking devices, there is a hope to expand the study into other demographics of Broad-winged Hawks. “We would like to learn more about migration in the smaller males and juveniles as they could have different timing and winter areas and thus different conservation threats.”  

Until then, Goodrich shares some notes on how we can help these remarkable raptors, “These amazing migrants are highly site-faithful on nesting and wintering areas. It is important we conserve forest areas throughout the range, including along migration routes to ensure their safe passage.” Her message is a sharp reminder that the conservation of our migratory species starts right in our communities. 

For McCabe, she is excited for the Audubon network to check out the migrations of previously tracked Broad-winged Hawks thanks to the Migratory Bird Initiative’s forthcoming Bird Migration Explorer. “I love that the Explorer will have an in-depth look at the migratory movements of Broad-winged Hawks. By incorporating tracking data, eBird, and range datasets, we can better understand the important areas Broad-winged Hawks and other species are using throughout their annual cycle.” 

To find out more information (including the most recent tracking map) and how you can support the project, please visit: www.hawkmountain.org/broadwing