Solitary Eagle’s Nest Discovered in Belize:Part 1

August 13, 2012 by  
Filed under Features

On the 30th of June, 2011, a startling discovery was made: the bulky, stick nest of a Solitary Eagle (Buteogallus solitarius) was found in picturesque, mountainous terrain of the Mountain Pine Ridge, Cayo District, Belize. The nest was sighted after a 52-year lapse in any documented breeding records on the species and is only the third nest ever located in the world. At the time of this writing, it is the only nest known to exist of this rare species in its entire range from Mexico to South America. The nest was situated in a pine tree on a steep hillside, overlooking valleys of thick, broadleafed vegetation. A single, nearly fledged eaglet, dark brown above with golden colored eyebrows, cheeks and throat was in the nest at the time of discovery. An adult Solitary Eagle, presumably the female, stood guard at the edge of the nest while its mate was hunting. The eaglet often stayed low in the nest, in the shadow of the adult, protected from direct sunlight.

For decades, birdwatchers, tourists and wildlife enthusiasts noted the presence of Solitary Eagles in the Mountain Pine Ridge Forest Reserve, and the species was undoubtedly breeding there, but no definitive nests were ever located. The 1995 A Guide to the Birds of Mexico and Northern Central America by Howell & Webb noted that many reports of Solitary Eagles had come from Belize, but that none had confirmed it as a breeding species. Jack Clinton-Eitniear, Director of The Center for the Study of Tropical Birds, documented in a 1991 bulletin that Solitary Eagles had been observed in the Mountain Pine Ridge as far back as 1969. One of the references Clinton-Eitniear listed to validate the existence of this rare species in the Guatemala – Belize region was the 1989 Maya Project: Progress Report 2, produced by the late Bill Burnham, Pete Jenny and C. Turley of The World Center for Birds of Prey in Boise, Idaho. Tikal National Park, Guatemala–where the observations were made–is no more than a “stone’s throw away” from the Mountain Pine Ridge Forest Reserve in Belize.

The elusive nest was discovered after a month-long, collaborative effort among six staff members employed by The Peregrine Fund. Five individuals: Stacia Novy, Camille Meyers, Jon Urbina, Audrey Martin and Matt Allshouse were hired to monitor and coordinate an Orange-breasted Falcon (Falco deiroleucus) release site in the summer of 2011. Dr. Scott Newbold was the acting field supervisor to the five attendants while on location. The sixth person, Roni Martinez of Belize, was paid by The Peregrine Fund as an intermittent consult to the project. A breeding pair of Solitary Eagles was regularly observed in the vicinity of the Orange-breasted Falcon release site and the five hack site attendants kept detailed observations on the eagles whenever one was sighted. Data collected included flight patterns, direction of movement, prey items, vocalizations and interactions with other raptorial birds. All sightings were reported to Roni, as he was a local ecotourism guide and familiar with the geography of the area. Although Roni was a Peregrine Fund employee, he worked fulltime at another locality and, consequently, was not present on the days the eagles were sighted at the hack site in June 2011. Stacia, the lead coordinator of the search, emailed sightings and data to keep him informed of any new developments.

As a licensed falconer and biologist, the author knew that breeding birds-of-prey will fly directly to the nest to feed eyasses while carrying prey items. She instructed her coworkers to closely follow the Solitary Eagle with optics anytime the eagle was spotted carrying prey. Unlike members of the genus Accipiter that utilize powered, flapping flight to navigate across the landscape, the Solitary Eagle is a large soaring bird, much like a Black Vulture (Coragyps atratus). Observations suggest it is a static soarer, using both convection currents (thermals) and obstruction currents (created by slopes and ridges) for movement. Knowing these subtle differences in raptor flight patterns and movement strategies proved critical in determining the location of the nest site. So, too, were traditional tracking skills possessed by the author. Stacia flew trained falconry birds for the first dozen years of her falconry career without radio telemetry. The knowledge she refined in tracking wild birds by sight alone, without the aid of modern technology, proved crucial to the nest discovery. The author relied on additional environmental cues, such as wind direction, mobbing behavior of other birds, alarm calls and raptor behavior to narrow down the nesting area.

Continued in Part 2

Article contributed by Stacia A. Novy

Photo: Solitary Eagle Nest

Caption: A female Solitary Eagle stands guard over the nest with a single
chick in the Mountain Pine Ridge, Belize

Solitary Eagle’s Nest Discovered in Belize:Part 2

August 13, 2012 by  
Filed under Features

To travel horizontally, a static soaring bird must descend and subsequently ascend using convective currents as an elevator, often in a slow cyclic pattern. The bird will enter a rising column of air at the bottom, ascend to the upper limits of the thermal, and then set its wings in a shallow, descending glide slope to move a linear distance. When the bird exhausts the momentum of its descent or nears the ground, it must intersect the bottom of another thermal to gain height and repeat the process. A bird that travels in this manner may have to work many thermals in succession in order to travel great distances across the landscape. Thus, soaring birds are keenly aware of the location, timing and prospect of air currents in their home territories; they will often use the same geological features or localities known to produce such currents and exploit them as “aerial highways”.

Two primary air currents used by the male Solitary Eagle–one an updraft and the other a downdraft–straddled the Orange-breasted Falcon hack site on opposite sides. The hack site was positioned on a peninsular, highland ridge, directly overlooking an unnamed river at the height of 2,000+ vertical feet, not far from Thousand Foot Falls, a popular tourist attraction. The eagle would ascend from the north, often carrying prey, soar directly over the hack site, and then descend the opposite side to the south in order to intersect another thermal further down the river valley. This initial descent, so near to the observation blind, gave one the impression that the eagle was “landing” in the forest directly below the hack site. Such a conclusion would be a mistake and is precisely the reason this particular Solitary Eagle’s nest went undiscovered for nearly a decade. Previous raptor biologists had erroneously searched for the nest in the forested slopes of this southern drop zone.

Only a person who could correctly interpret the eagle’s flight patterns would be able to ascertain a final descending glide into a nest. When a soaring bird is truly landing, it will stiffly set its wings, rotate the feet forward, angle the head and body toward the intended perch and glide in a fast, direct fashion. It will not ascend lazily into the air again. Once the general landing area of the food-carrying male eagle was defined, it was a simple matter of setting up surveillance points along its route of travel to pinpoint the nest location. The Peregrine Fund attendants manned three observation points that intercepted the eagle’s trajectory for four days before locating the actual nest tree.

The male Solitary Eagle was first seen at the hack site on 7 June 2011, the day the attendants arrived to prepare the hack tower for the Orange-breasted Falcon release. Regular sightings occurred at the hack site every two- three days thereafter between 1000 and 1500 hours, when wind and thermal activity was at its peak. After two weeks of continuous observation, surveillance points were marked along the eagle’s known flight path by 27 June 2011, and sightings began to occur daily, as the attendants drew closer and closer to the nest. Roni Martinez was invited by the author at that time to assist in the search–after the general nest location and flight path were known–to help the hack site attendants monitor surveillance points with an “extra set of eyes”. As a native conservation officer, Roni was also needed to negotiate passage through a military weapons training area adjacent to the suspected nest site, as it was decidedly foolish for American foreigners to be caught trespassing across this dangerous, and possibly restricted, zone without permission.

Continued in Part 3

Article contributed by Stacia A. Novy

Photo: The Peregrine Fund Crew

Caption: The “Solitary Eagle Search Team” employed by The Peregrine Fund,
Boise, Idaho