Realm: Terrestrial
Climate: Temperate
Biome: Temperate broadleaf and mixed forests
Central latitude: 38.610000
Central longitude: -79.834720
Duration: 22 years, from 1962 to 1983

213 records

20 distinct species

Across the time series Setophaga magnolia is the most frequently occurring species

Methods

The census area is a 6.08-ha rectangular plot (100.6 m x 803.6 m) centered on the road and one of the narrow trails. This area was censused by the spot map method (Hall 1964) in 1947 (Stewart and Aldrich 1949). In 1948 the members of the Brooks Bird Club began a series of censuses by the spot-mapping method made in early June which have continued to the present at 5-year intervals (DeGarmo 1948 1953; Hall 1958; Hurley 1964; Koch 1968; DeGarmo and Koch 1974; Phillips 1979 1984). In 1959 a program of annual censuses by a rather different index method was begun. The method adopted has the merit of giving a satisfactory index of the number of territorial males in a minimum amount of time-one overnight trip to the area. The index method consists of traversing the length of the study area in a fairly rapid fashion tallying all the birds seen and heard during the traverse. This traverse requires about 12 min to complete. After a wait of about 3 min the area is traversed in the reverse direction. This down-and-back procedure is then repeated giving four traverses of the same route. One set of four is made during the last hour before dark (approximately 19:45-20: 45 EDT) and another set of four is made in the first hour of daylight the next morning (05: 30-06:30). After the evening counts a tentative judgment is made as to the probable number of singing males of each species on the area and at the end of the morning counts final judgment of the population is made. Counts of this nature have been made in the last 2 days of May or the first 2 days of June from 1959 through 1983. All counts through the years were made by the same observer. In the early years the index method counts were not too reliable while the method was being worked out but with added experience the later counts have been good measures of the population. In 1973 1978 and 1983 an additional index method count was made later in June to give some idea of the variation expected by this method. This comparison is given in Table 1. It is noted that most of the rarer species agree exactly but that some of the more numerous species differ by ? I male and the total population varies by ?2 males. In 1983 this variation in the Yellow-rumped Warbler and the Swainsons Thrush may have been due to the arrival of late migrants. In 1964 1968 1973 1978 and 1983 it was possible to compare the index method results with those of the more conventional spot-mapping method (see Tables 2 3 4). For species with small populations the two methods agree quite well but for the abundant species the index method appears to overestimate the population. This happens because this method makes no al- lowances for the fractions of certain territories being outside the boundaries of the study area. The difference is slight for individual species but the accumulated error in the total population is sometimes large. In 1983 when allowances were made for this effect the population estimates agreed almost exactly. The accuracy of the index method is highly sensitive to the weather. Inclement weather on the one day selected for the count can cause large errors. This is the apparent cause of the low count for 1967 made in a cold drizzle on the only 2-day period available that season. mark_recapture Unit of abundance = IndCountInt, Unit of biomass = NA

Citation(s)

Hall, G. A. (1984) A Long-Term Bird Population Study in an Appalachian Spruce Forest. The Wilson Bulletin, 96, 228–240.