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An Annual Fall Ritual: Raptor Migration 

Hawk watching is an exciting autumn event, returning after a hiatus in 2020

Each fall, birds of prey wing their way southward across Oregon during their annual migration or winter movement. Some come as far away as the Arctic and one, the Swainson's hawk, departs from its breeding grounds across North America and heads for the highlands of Argentina, although some small populations winter in Florida, Texas and California. The migrant raptors spend the breeding season in northern regions but as prey availability decreases in the fall and winter, the birds fly to more southern areas to spend the winter before returning north in the spring.

The term "raptor" is derived from the Latin rapere, which means to plunder or to seize—an apt description for this group of predatory birds with traits such as excellent eyesight for locating prey, sharp talons for grasping prey and hooked upper bills for tearing prey apart. Though the term "raptor" includes owls, these mostly nocturnal predators differ from the diurnal hawks, eagles and falcons.

The view from Bonney Butte keeps hawk watchers engaged even on slow days. - COURTESY OF HAWKWATCH INTERNATIONAL
  • Courtesy of Hawkwatch International
  • The view from Bonney Butte keeps hawk watchers engaged even on slow days.

Across the West are various hawk watching locations where biologists gather to record the species and number of birds that pass by sites in Washington, Oregon, Utah, California, Montana and Alberta, Canada. Locally, the East Cascades Audubon Society monitors a spot up on Green Ridge above the Metolius River while Hawkwatch International, based in Salt Lake City, staffs Bonney Butte on the southeast side of Mt. Hood to record the passage of these apex predators during the fall.

So why look at these birds to begin with? Collectively, these birds are atop the food chain, and disruptions in that chain due to wildfires, pesticides, low prey density, and more, is an indication over the long term that something is amiss in nature.

"Long-term data from these efforts can be used to assess whether counts of migrants for different species are stable, increasing or decreasing," said Dave Oleyar, Ph.D., HWI director of long-term monitoring and community science. "Trends from a network of sites can paint a broader picture—are declines local to one or two sites, widespread across a certain area, or continent-wide? This knowledge can help direct focused research to understand declines."

David Vick, the East Cascades Audubon Society's Green Ridge project coordinator, provided some history about the group's hawk watch location on Green Ridge, a long promontory above the Metolius River.

"Prompted by HawkWatch International's 1994 trail count on Green Ridge, members of what was then the East Cascades Bird Conservancy scoured the 15-mile-long ridge in 2004 in search of a survey site." HWI moved its hawk-watching activities up to the Bonney Butte site for various reasons, so the Central Oregon birders began their search.

Several ECBC members scoured Green Ridge for a suitable location and in 20004, member Kim Boddie discovered a location with excellent views to the north, east and west.

"The first official Green Ridge Fall Raptor Survey was conducted in 2005 and this volunteer citizen science project is now under way on its 15th year of data collection," said Vick. The group missed counting in 2014 because of the Bridge 99 Fire and 2020 due to the COVID-19 pandemic.

The majority of count days for the Green Ridge site are held in September and October on weekends with a few weekdays thrown in depending upon volunteers. At the viewing location, the members and participants set up spotting scopes and focus their binoculars on both distant and close-up areas to spot raptors.

click to enlarge A red-tailed hawk pauses atop a sign during its fall migration. - DAMIAN FAGAN
  • Damian Fagan
  • A red-tailed hawk pauses atop a sign during its fall migration.

"Although hawk watching can be two hours of nothing but scenery followed by 20 seconds of adrenaline, we are always hopeful of being present on a big day, which keeps us coming back again and again," said Vick. "In addition to myself acting as the project coordinator and counter, Peter Low is our unparalleled official observer and has been the driving force behind this project for many years."

On ECAS's first weekend of this year, September 11 and 12, the group recorded 199 birds of prey migrating south. A 200+ bird day is not uncommon and the group's all-time daily high was 420 birds. Daily totals are posted online through Central Oregon Birders Online and Oregon Birders Online, as well as to a database maintained on Hawkwatch.org. The data from hawkwatch sites across North American is compiled into a Raptor Population Index, which is updated every three years.

"The Raptor Population Index uses count data from across North American to assess the status of raptor populations using migration data," said Oleyar. "Migration counts are a common and efficient way to effectively take the 'pulse' of regional populations for a group of species that are generally dispersed and/or secretive many other times of the year." The data is available to land management agencies and conservation organizations, as well. At the Bonney Butte and Green Ridge hawkwatching sites, 22 and 18 species, respectively, of eagles, hawks, falcons, vultures, osprey, and harriers have been recorded.

So, what is the status of birds of prey these days?

"Twenty-six years of migration monitoring at the Bonney Butte HawkWatch shows overall stable numbers of total migrating raptors with year-to-year fluctuations, however, during that time, we have seen declines in the counts of American Kestrels, Golden Eagles, Northern Harriers, Red-tailed Hawks and Rough-legged Hawks," added Oleyar. "We've seen increases in counts for bald eagles, peregrine falcons and turkey vultures at the Bonney Butte HawkWatch." The increases in bald eagles and peregrine falcons can be attributed to successful reintroduction programs that were initiated for these two species when they were listed under the Endangered Species Act.

Volunteers scan the skies for migrating raptors at the Green Ridge Hawk Watch Site. - CHUCK GATES
  • Chuck Gates
  • Volunteers scan the skies for migrating raptors at the Green Ridge Hawk Watch Site.

Species showing declines trigger local reviews or conservation efforts, which may target various impacts to the populations, including wildfires, prey abundance, pesticides, habitat loss, collisions with vehicles or building, diseases, electrocutions on power lines and trapping or shooting. Though protected by law, indiscriminate killing of raptors occurs in areas where birds such as Cooper's hawks or northern goshawks prey on backyard or farm poultry.

One difference between the two sites, other than location, is that HWI live-traps raptors at its Bonney Butte site, taking body measurements and affixing a uniquely numbered USFWS band to the bird's leg. "Most days we also trap and band migrating raptors, so there's a chance you might be able to see one close up before our crew releases it," said Oleyar. "Mount Hood offers a stunning backdrop for watching migrating raptors, making it worth the trip even on slower days."

The final count weekend for Green Ridge is planned for October 23-24, but if the weather remains good, volunteers may be out counting on the last weekend of October. The Bonney Butte count will continue through October; check the website for updated access conditions and hours of operation. Vaccinated birders are encouraged to visit the site and are reminded to adhere to state masking guidelines for outdoor activities.

Not to worry if you miss out visiting Green Ridge or Bonney Butte, as many birds of prey winter across Oregon providing ample opportunities to view these magnificent birds of prey.

ECAS: ecaudubon.org

HWI: hawkwatch.org

Bonney Butte Seasonal Report: dunkadoo.org/explore/hawkwatch-international/bonney-butte-hawkwatch-fall-2021

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