Third Decennial Census of Kirtland's Warbler

Abstract

KIRTLAND'S WARBLER (Dendroica kirtlandii) was discovered in 1851, and since that time has always been considered a rare bird. The discovery of the nesting ground in 1903 revealed habitat so specialized and restricted that I doubt the population was much larger at any time in recent centuries. A momentary upsurge may have occurred in the period 1870-1900 when collectors took a number of specimens on the wintering ground in the Bahama Islands. Significantly this was the time of most active lumbering and most extensive forest fires in the breeding range, when optimal nesting habitat was probably the greatest in hundreds of years. Until 1951 no one knew even approximately how many Kirtland's Warblers existed, because no one had visited more than a fraction of all the nesting areas. Then, on the hundredth anniversary of the discovery of the species, I organized a group effort to seek out every nesting location and count all the singing males; we repeated the count in 1961 (Mayfield, 1953, 1962). These two censuses 10 years apart showed no essential change, suggesting the population was holding steady at about 500 pairs, but my data on individual nests, heavily weighted with information from the 1950s, showed an ominously low production of fledglings (Mayfield, 1960). Now in the census of 1971 my worst predictions have been realized. The total count of singing males sank to 201, a decrease of 60 percent in 10 years. Table 1 summarizes the results of all three censuses.