Alaska Off-road Breeding Bird Survey

Patterns Bird of Distribution

These maps and tables display for each species the average number of birds counted each summer from 1993-1997 on each Alaska Off-road Breeding Bird Survey route. Most routes consist of a series of 12 stations separated by at least 250 m along small foot trails or across the backcountry. At each station an observer records all birds seen or heard during 5 minutes out to an unlimited distance. Surveys are conducted at sunrise once each summer, generally between 10 and 30 June, and by the same observer when possible. A few routes consist of as few as 5 or as many as 25 points. For these, route totals are adjusted to reflect the number that would have been counted on 12 points.

The number of birds detected during a survey represents some unknown fraction of the total number of birds present in the area. The proportion of birds counted on any particular survey depends on many factors, including the observer's hearing ability, the density of the vegetation, and the birds' singing rates. Singing rates can be influenced by a bird's mating status, time of season, time of day, and weather. Because of all these factors, the numbers of birds counted on different routes cannot be compared directly as measures of abundance. Certain species are not represented well because of seasonal timing, diurnal timing, and land-based sampling of these surveys. These include early-nesting species such as ptarmigan and grouse, nocturnal species such as owls, and waterbirds such as loons, grebes, geese, ducks, and seabirds.

The symbols on the maps show the distribution of the routes surveyed and the relative numbers of birds detected. These can be used to discern general patterns of distribution. Absence of a species in an area may simply reflect a lack of surveys in suitable habitat in that area rather than the species' actual absence. Higher relative densities may reflect higher detectabilities of birds in a particular habitat rather than higher actual numbers of birds. Similarly, comparisons can be made among species for general patterns of distribution but not for abundance because of marked differences among species in detectability. As we increase the number of routes in different habitats across the state, we will improve our understanding of the patterns of distribution of these birds.

Alaska Science Center - Biological Science Office