Reflections on Bird Migration, Habitat Use, and Bird Song in the Pacific Coast Migration Corridor

We need time to reflect on and understand the patterns and processes in a new area or changing situation. New challenges require time to adjust, to shift, or to change a way of perceiving. I am referring to birds as they respond to a changing world with regard to climate change, habitat fragmentation, or learning their “tribe song,” and I am also referring to anyone learning about bird dialect, range variability, and habitat selection. In 2013 and 2014, I studied birds in the Pacific Northwest (PNW) using eBird and IBird, citizen-based monitoring applications developed by the Cornell Lab of Ornithology. IBird provides a means to analyze data and communities, and universities use it to educate people about birds (Prestby 2015; Armistead and Vyn 2016). The interactive mapping tool is accessible to a huge database (Figure 1). Other bird monitoring programs include Christmas Bird Count, North American Breeding Bird Survey, Backyard Bird Survey, and International Migration Count.

Citizen-based monitoring has a long history on a global scale, nationally and locally. The Christmas Bird Count was organized by the National Audubon Society more than one hundred years ago, and interest has increased among citizens to participate in science and contribute to large databases of information. The Environmental Protection Agency states that Federal agencies use sixty-two percent of databases by volunteers, and federal agencies rely on thirty percent of these databases for decision making. With eBird, data quality is efficiently kept in check. An expert birder is enlisted to be a stopgap for questionable records, and a detailed description and photo are required to prove rare sightings. In Wisconsin, some records that were not accepted included a black-headed grosbeak (it was a rose-breasted), black-throated gray warbler (not enough detail), and spotted towhee (could be a hybrid Eastern/spotted) (LaPuma and Heikkinen 2015). All of these species have western ranges, and accidentals do occur.

Figure 1.

Species data using eBird. Left column, top to bottom, and right upper panel: Population abundance in Oregon using eBird for varied thrush, hermit thrush, black-throated gray warbler, and pileated woodpecker, from 2000 to 2016. Bottom right panel: Occurrence of Pacific-sloped flycatcher in birding hotspots (teardrop with flame) and in other individual birder records (solid teardrop).

Bursting with Birds in Costa Rica

I began the journey where many birds congregate during the winter months—in Costa Rica. Local bird species sang with abandon in Costa Rica while familiar U.S. species did not sing at all. Migrators from their northern extent had just finished their nesting season. The Costa Rica Conservation Foundation restores tropical forest in Premontane Wet and Premontane Moist life zones on the Pacific slope. The Foundation studies the decline of the three-wattled bellbird to identify a Bellbird Biological Corridor from the continental divide to the Gulf of Nicoya. The three-wattled bellbird can take six years to learn its song, with some males continuously modifying their song, depending on nearby individuals. Not only are separate dialects heard over their range, but some populations utilize multiple dialects such as the Monteverde (Kroodsma et al. 2013).

Costa Rica supports a host of birds that occupy diverse habitat and then migrate to North America to breed. For Neotropical migrant songbirds, the long-distance migration is energy-expensive. For instance, the Swainson’s thrush utilizes lowlands in spring, arriving with reserves enough to cross the Gulf of Mexico on its return north along the Pacific migration corridor (Wilson et al. 2002). With fuel, individual Swainson’s thrushes can leave stopover sites quicker and avoid using land that is in jeopardy from development (Newton 2006; Papes et al. 2012). Fortunately, the bird community thrives in the many coffee plantations in the country.

The crucial first step to survival in all organism is habitat selection. If you get to the right place, everything else is likely to be easier.

—E. O. Wilson 1984

Approximately two-thirds of the birds in North America migrate; the colder the area, the more migrants...