Contributed by John Goodell, avian researcher and wildlife biologist.
In 2015, a bird banding effort was launched at the Indian Ford Aspen Restoration site near Sisters, in collaboration with the USFS, DCFP, Oregon Zoo, Oregon Wildlife Foundation, and others. The bird monitoring station is intended to evaluate the avian population response to aspen restoration along Indian Ford Creek. Now in its fourth year, the project is poised to document conservation success in-action.
The practice of banding wild birds with metallic inscribed rings or plates dates to the zenith of falconry in Eurasia. Marco Polo, in describing falconry in Asia wrote, “Each falcon belonging to the sovereign and the Barons, has a tablet of silver on its feet with its name and that of its owner inscribed so that wherever caught it may be returned to him.” In 1595, one of Henry IV's banded Peregrine Falcons was lost in pursuit of a bustard in France and was discovered in Malta a day later, about 1350 miles away, demonstrating the speeds possible by peregrines in migration.
Early European falconers not only banded their prized falcons to identify ownership but also banded herons captured by their falcons. The “ringing” flight of a falcon on a large Grey Heron was considered a testament to the falcon’s courage and stamina – the intent was not to kill the heron, but witness the climbing pursuit, and then release the heron if captured. In 1669, Duke Ferdinand placed a silver band on a Grey Heron caught by his falcon, which was recovered by his grandson decades later, documenting a longevity mark for that species. In 1710 a German falconer captured a grey heron with several rings on one leg. Some rings were unidentified, but one was placed on the heron in Turkey, more than 1200 miles to the southeast – confirming a migratory route for that species.
How far to various species migrate? Where do they migrate to? How long do they live?
By the late 19th Century, ornithologists in North America and Europe began to develop scientific bird programs. These efforts were designed to help answer several important questions: How far to various species migrate? Where do they migrate to? How long do they live? But late in the 20th Century biologist began looking to banding methods to answer crucial conservation questions.
In particular, conservation biologist became increasingly concerned about the rate of deforestation in both North and South America. Of particular concern were neotropical migrant songbirds like warblers, vireos, flycatchers and others that over-winter in the tropical forests of South and Central America, but breed in the temperate forests of North America.
Like many other avian guilds, neotropical migrants are excellent indicators of habitat quality due to their species diversity (or “richness”), the specific habitat requirements of each species, and the conspicuousness of their plumage and songs – making surveying efforts very practical. Early neotropical migrant monitoring efforts showed alarming trends: Forest species seemed to be declining across the continent.
In the West, particular concern was focused on species associated with riparian streamside habitat, cottonwood gallery forests, and aspen forests. Early commercial beaver trapping, grazing in desert riparian zones, dams, diversions, fire suppression, and conifer encroachment snowballed into a perfect storm of impacts, resulting in over 90% loss of these critical habitats in many Western states. Unfortunately, over 80% of bird species in the arid West rely on these vital deciduous habitats for some aspect of their life history.
But initial bird survey efforts relied on programs like the Breeding Bird Survey, where volunteer observers listened and watched for birds at several stops across an established route. Such data was collected nationally, and scientists analyzed it looking for population trends. Although some trends were discernable, scientists discovered that observer biases (I.D. abilities, vision, hearing, etc.), lack of consistent effort, and lack of consistent methods were confounding the results.
Furthermore, scientists realized changes in the number of birds counted in an area do not necessarily prove a relationship to population trends. Known as a “population sink,” some areas may exhibit large numbers of birds, with low reproductive success due to habitat degradation, disturbance, contaminants, or other causes. For example, if 75% of available habitat is cleared, subsequent surveys in the remaining parcels may show extremely high abundance, while reproduction may be low due to overcrowding and poor foraging resources. It was increasingly clear that counting birds by sight and sound may not accurately capture population trends. These and other issues helped focus the questions posed by ornithologists, and the methods used to answer them.
What is the relationship between habitat change and bird population trends?
Population studies are challenging without measuring specific criteria: Survivorship: How long are breeding adults living? Productivity: How many offspring are they having year-to-year? Recruitment: How many offspring are being recruited into the breeding population? Once these criteria are measured over time, scientists can measure rates of change, called Vital Rates and compare these changes with habitat changes. As a result, North American ornithologists developed the Monitoring Avian Productivity and Survivorship (MAPS) a standardized method using bird mist netting and banding to measure population trends in breeding birds at specific sites.
Ten mist nets are placed in a target habitat, and they are opened multiple times throughout the breeding season for six hours a day. Birds are retrieved, identified, measured, banded, and released. The station is operated for multiple years and is ideally designed to measure the effect of habitat restoration on bird populations.
Now in its fourth year, the station at Indian Ford Creek had operated two years before restoration work began, one year during restoration activities in 2017, and will operate for at least 7 more years post-restoration pending funding. Banding results are expected to document a significant population response from aspen associated landbirds post-restoration, such as western wood-pewees, black-headed grosbeaks, house wrens, warbling vireos, red-naped sapsuckers, and more. But the improved foraging opportunities expected from increased aspen habitat should also benefit riparian bird species, such as yellow warblers, willow flycatchers, and others.