Winter Population Dynamics of Blue Jays, Red-Headed Woodpeckers, and Northern Mockingbirds in the Ozarks

Abstract

Numbers of blue jays and red-headed woodpeckers in the Ozark region were examined to determine relationships between these two acorn-storing species during winter, using data from 49 Christmas Bird Counts conducted between 1957 and 1982. Numbers of northern mockingbird, a frugivore, were compared. Although red-headed woodpeckers occurred irregularly at over 90% of the count areas, and although blue jays were far more numerous than woodpeckers, abundances of these two species showed statistically significant positive correlations in 74% of the areas. When effects of long-term population changes were statistically partialed out, blue jay and mockingbird numbers were significantly correlated in 29 To of the areas, but red-headed woodpecker and mockingbird numbers were correlated in only 10% of the areas. These results suggest that the significant relationship between blue jays and red-headed woodpeckers does not hold for all species wintering in the Ozark region, and are consistent with the hypothesis that the former two species covary as a function of mast crop availability. Comparisons within count areas of year-to-year variation in numbers of birds suggested that, in the Ozark region over the last 25 years, blue jay numbers have generally increased and mockingbird numbers have generally decreased in northern areas, with no obvious trend in red-headed woodpecker numbers. Few comparisons (< 10 To) of year-to-year variation in bird numbers between count areas were significant for blue jay or red-headed woodpecker, although synchronous woodpecker fluctuations apparently occurred in eastern Kansas and northwestern Missouri. More than 25 To of the correlations between count areas for numbers of mockingbirds were significant, suggesting that many areas within the Ozark region have experienced similar fluctuations in mockingbird numbers. Numbers of all three species were compared with yearly estimates of acorn and mast abundance in Missouri from 1959 to 1980. Red-headed woodpecker and blue jay numbers were significantly correlated with mast abundance in Missouri at more count areas than were numbers of northern mockingbird. This relationship between bird numbers and mast abundance was stronger in the Ozark Plateau region than in Missouri as a whole. These results are consistent with the hypothesis of mast influence on jay and woodpecker numbers. Red-headed woodpeckers appeared more sensitive than jays to changes in mast abundance, and increases in numbers of jays may also be due to increasing urbanization in the Ozark region.