San Francisco Bay’s Hawk Watchers

There I met up with Allen Fish, director of the Golden Gate Raptor Observatory (GGRO) since 1985, who looked at the fog with optimism and stated that it “looked like it was beginning to clear.” With a laugh he also mentioned that the day I arrived was the first foggy day in their 2008 survey season. But true to his forecast the fog soon lifted and a fantastic 360-degree view of Hawk Hill revealed the Marin Headlands in all its hawk migration glory.

The project on this hill started in 1983. The National Park Service’s Resource Ecologist Judd Howell called upon falconer Will Shor and birder Carter Faust for help creating a daily program originally titled the “Golden Gate National Recreation Banding Program” that banded and counted hawks in the Headlands. Howell insisted that the Park staff share the project as a cooperative venture with the GGNRA’s non-profit partner, The Golden Gate National Parks Conservancy, and thus ensured the Observatory’s longevity.

A typical migration season for Hawk Hill is from mid-August to mid-December. Employing from 150 to 200 volunteers each season, along with three staffers, the GGRO has blossomed into a nationally-recognized bird monitoring system in which anyone from pro to amateur can participate. Hawk Hill also provides a great opportunity for families and non-eccentric-birders like me to stop up and see up to 19 species of hawks, eagles, falcons, vultures, osprey, harriers, and kites.

Hawk Watch

Up on Hawk Hill with Allen Fish, the wind blew furiously through the quadrant system—GGRO’s migration-counting technique in which volunteers are stationed in all four directions. The count was up and running when we walked up, with at least three warmly bundled hawk-counters at each side and a recorder sitting in the middle, clipboard at the ready.

“Coming at you West! At the Red Spot! Another adult Accipt! Flying left, you got ‘em?” called volunteer day leader Bob Power, executive director at the Santa Clara Audubon Society. The counters conferred briefly and the little raptor was determined to be a Sharp-shinned Hawk.

“Got it!” yelled Julie Sykes, the recorder for the current shift as she made a tally on the raptor field form. The day had almost been a fog-out but Hawk Hill now promised to live up to its name.

Suddenly out of nowhere, a shadow crossed the ground. In the split second I had to look up and see its origin, I made out the pale belly and underside of the wings, and then I spotted it: the tell-tale black patagial marks—less gracefully called ‘blacked armpits’—and realized it was a juvenile Red-tailed Hawk! Not more than five feet over my head! Exclamations of surprise and delight came from all four corners, with a few moans of regret from those who had missed it.

GGRO Hawk Watch data helps scientists and researchers answer many questions about the migration, such as how many total birds are coming through the Marin Headlands? What are the migration rates for each species? Is their population steady, declining, or rising over time? “To count every bird that comes within the 360-degree view is difficult,” Fish states. “Therefore the watchers keep track of the rate of migration. We call it hawks per hour.” This method of tracking the rate of raptor activity and not the actual number of individuals “keeps counters from going more than a little crazy trying to tell the difference between a Red-tail that comes through at 10 o’clock and a Red-tail that comes through at 3.”

Aluminum Bands

Bird banding is an old practice still used in modern times although the techniques have changed somewhat. Silver bands and cords were used centuries ago. Today, banders use aluminum rings. A trained team of volunteers use blinds, bow nets, and lures both mechanical and live to capture and carefully band the leg of every inexperienced raptor that gets caught while seeking a quick migration meal. 

When a juvenile Red-tailed Hawk was snagged at a nearby hilltop called Slacker Hill, I could hear the excited voices on the GGRO walkie-talkies on Hawk Hill. Around 1 p.m. a GGRO bander brought the Red-tail, a shiny aluminum band already on its leg, to a waiting crowd and spoke about the banding program. He mentioned how the banding team checks the health of every bird they capture, then the crowd ‘ooh-ed’ and ‘ah-ed’ when the hawk was released right in front of them. 

Since Allen Fish had told me about the banding demonstration before the rest of the crowd heard about it, I was luckily able to find a choice spot. I gazed into the intense yellow eyes of the remarkably calm Red-tail, and was again reminded just how important Hawk Hill is in educating the public about the biology and conservation of these magnificent birds. 

In the past the banding program used live birds as lures, usually starlings or pigeons with leather saddles wrapped around and under the bird. While the team would do its best to pull the lure bird out of talon’s way, there have been a few casualties over the years. Recently GGRO has sought other means to lure in raptors. Using a French toy model of a mechanical bird based on an idea from Leonardo da Vinci, scientists have shown promise in replacing live birds.

Once a mechanical Northern Mockingbird—a gear body covered with real feathers—attracted a Golden Eagle who promptly tore the lure to pieces before realizing its mistake. After nearly dragging the young woman holding the string behind a blind, the eagle flew away seemingly to escape but ended up caught in a net made of finely woven mesh called a mist net—one of the main tools in capturing birds. The “RoboLure” received the most glorious death any robotic bait could ask for. To this day it remains framed at the GGRO private headquarters along with the net that made the capture and a little card caption explaining its significance.

Bird banding answers a different set of questions that still utilizes GGRO’s hawk counts: now that we know how to measure population change in the hawk counts, how do we know where these migrants are coming from? Where have they nested? Where will they winter? Are Red-tailed Hawks coming from Alaska or just from northern California? Are they going to Mexico or to Argentina or all of the above? There is a difficulty in gleaning information from banding since there are so few band recoveries; about three out of 100 bands are returned to GGRO and the rest, who knows? But with nearly 1000 band recoveries for GGRO raptors banded from 1983 to 2008, the migration map is starting to take shape.

Tracking Them Up, Down, Backwards, and Forwards

While banding is an act of faith in terms of recovery, there is little known about the bird’s activities between banding and retrieval. Radio telemetry can allow trackers who actually chase the hawk to learn the route taken, find locations of its roosts, and see where it stops to eat. Once a year at GGRO, a radio transmitter the size of a Bic pen cap and weighing between 5 and 9 grams (depending on the size of the bird), is glued onto one tail feather of 2–3 hawks and is further secured with three strings—in the following spring the tail feather simply molts off, taking the gear with it. A team of three cars with two people per car follows each hawk to best gather data and triangulate the hawk’s location. The team tracks the bird until it crosses international borders or the device is no longer operational or useful. Radio trackers are trained two full days to decipher pager communication codes, find regional high points to get the best signal reception, and to keep in constant contact with one other. The leader of the team has to know where to find the highest peaks in the area that the bird is moving toward. She must factor in travel-times and topography and make decisions about how far a hawk might go in a day. In all, the tracking team leader must outguess the hawk’s flight.

But even with the best planning things do not always go as intended. One radio-tracked Broad-winged Hawk was successfully followed for four days on a southbound beeline. It crossed the border into Mexico, but the team could not follow since they did not have the necessary permits. Once, a group of GGRO trackers spent three days closing in on a beep that did not move. After conferring, they decided to close in and risk causing the bird to move, which normally they would avoid. On the morning of the third day, thinking that the bird must be dead or the feather had been plucked off, the team ended up closing in on a cabin that had a police scanner broadcasting a beep at the same exact frequency that they were using. Their hawk had given them the slip.

The GGRO also learned that putting the transmitters on the tails of Cooper’s Hawks was much more difficult than for larger hawks. In the mid-1990s three out of five male Coopers’ pulled out their own burdened feather; this at first was thought to be accidental or just a quirk of one bird, until two more were found from different hawks. One feather landed on the very summit of Black Butte in Oregon, a 3,000-foot pile of rocks. The volunteers hiked for six hours to retrieve the transmitter. Once GGRO staff realized that this method of tracking was stressing these accipiters, they promptly stopped putting transmitters on Cooper’s Hawks.

What Have We Learned?

Looking back on the data collected, both volunteers and researchers were surprised to see that more than half of the hawks funneling down the Marin Headlands each autumn did not actually travel south for the winter as was previously thought. Another interesting fact was that the majority of the birds flying through San Francisco’s peninsula were juveniles. Why would they not migrate south? Why so few adults? “Great winter climate right here,” states Fish simply. “The hawks don’t need to move south.” As for all the young birds funneling down along the coastal headlands, it could very well be that they just do not know any differently. This “coastal effect” was first described by C. J. Ralph, research wildlife biologist at the US Forest Service’s Redwood Sciences Laboratory, who theorized that younger birds have not yet learned the many inland, and potentially safer, migration paths that are available. As the California coast provides stable northwest tailwinds and a clear north–south leading line to guide the hawks, it appears that for young birds traveling south, the coast is the best way to migrate. However, these inexperienced hawks may also be more inclined to be blown off-course by a strong autumn storm. A hawk blown a few dozen miles west out over the Pacific Ocean may have little chance of finding the coast again. 

One particular trend the GGRO volunteers have noticed is for small falcons: the counts for American Kestrels—measured in relation to the counts for Merlins—have recently been declining. The national datum on the small kestrel, once thought to be high in population numbers, has been showing some worrisome trends in the 2000s, as much as 4% annual declines in parts of the northeast. In the 1970s, Hawk Hill’s co-founder Dr. Laurence Binford reported counting 276 American Kestrels during 263 hours over 6 years, and not a single Merlin to speak of. In 1997, GGRO’s kestrel count amounted to 750 sightings, with kestrel counts at the Golden Gate averaging 663 kestrels per autumn through 2006. But recently, in 2007, the count for kestrels was only 378. 

So, here are the numbers for small kestrels at the Golden Gate for the past few decades: in 1983, the American Kestrel-to-Merlin ratio was 89:1. It was 30:1 in 1984, 16:1 in 1985, and skipping ahead to 2007 it was 2:1. While several possible reasons—such as West Nile Virus, pesticides and habitat loss—have been considered for the kestrel’s declines, Fish believes that not one but several of these forces combined have negatively affected this usually adaptable bird.

Spring, the Purveyor of New Possibilities

Allen Fish long believed that the autumn migration was Hawk Hill’s only raptor season, after all, “the northwestern winds would favor a southbound flight and discourage a northbound one.” But in March 2005 volunteer Steve Bauer discovered that the Marin Headlands just may have a migration in the spring as well. While watching a nesting pair of Peregrine Falcons near Hawk Hill, Bauer could not believe it when he witnessed the male Peregrine dive at an adult Common Black-Hawk. The Black-Hawk was soon followed by a similarly northbound Prairie Falcon. Later that same day Sharp-shinned, Cooper’s, Red-tails, Ospreys, Northern Harriers, and one first-year Golden Eagle followed suit.

“The spring flight is exciting partly because some of the hawks are molting already,” said Fish. “A bird in mid-molt has different patterns that can sometimes be read to tell what age the bird is.” A juvenile Red-tailed Hawk for example, would have dark bars at intervals on its tail before having the adult nearly-solid red hue.

There are fewer raptors during the spring migration, possibly because these travelers must contend with a north wind head on and possibly because the winter mortality rates for the hawks are estimated at around 50%. The Headlands, however, block some of the north winds, and the west wind funneling through the Golden Gate provides “a great shot of air,” as Fish puts it, that creates a boost—or lift zone—against the west-facing hills. 

The Marin Headlands spring migration will no doubt unfold new opportunities for raptor study and data collection, which may answer questions about the hawks’ return trip. Yet only time will reveal such results and my stay had come to an end; I gave one last look around the Hill, admiring the dedication of these volunteers that kept them returning whenever they could. As I drove down the winding road and headed for the freeway, I was already making plans for when I could visit again. Hopefully, on the next trip no looming blankets of fog will prevent visibility of these wonderful creatures.