Mast Production and Winter Populations of Red-Headed Woodpeckers and Blue Jays

Abstract

In 17 Missouri counties in which Christmas bird counts have been conducted, patterns of mast production since 1960 were compared using annual fall mast survey data collected by the Missouri Department of Conservation. Within most counties a positive relationship existed among walnuts (Juglans spp.), hickories (Carya spp.), and white oaks (Quercus spp., subgenus Lepidobalanus) for both numbers of trees with heavy mast crops and a mast production index. Mast production by red oaks (Q. spp., subgenus Erythrobalanus) also was generally positively correlated with those 3 mast groups, even though red oak acorns take 1 year longer to mature than nuts from the other 3 groups. To compare mast crops initiated in the same year, the red oak mast data were lagged 1 year and compared with the other mast groups. The weak results from that analysis suggest that factors affecting acorn growth are more important than factors affecting seed set in mast trees. Mast production of pecan hickories (Carya illinoensis) seemed unrelated to the other 4 mast groups. Results of this study demonstrate that mast production among a variety of tree species was synchronous over relatively small areas. Within most of the 17 counties examined, a positive relationship existed between acorn abundance and wintering numbers of red-headed woodpeckers (Melanerpes erythrocephalus), a species that relies heavily on acorns as a winter food source. No such relationship was found between acorn abundance and wintering number of blue jays (Cyanocitta cristata), a species that stores acorns in the fall, but uses a variety of winter food sources. This suggests that dependency on mast crops as a food source determines how closely animals track changes in mast abundance. J. WILDL. MANAGE. 51(2):459-467 Mast has long been recognized as important food for many birds and mammals; e.g., Lay and Siegler 1937, Van Dersal 1940, Cypert and Webster 1948, Christisen and Korschgen 1955, Perrins 1966. Despite that importance, surprisingly little is known about temporal or spatial patterns of mast abundance in North America (e.g., Bock and Lepthien 1976). Most reports concerning mast abundance have focussed on small areas for short periods of time (e.g., Burns et al. 1954, Gysel 1956, Sork 1983) and many reported abundances are anecdotal (e.g., Bagg 1969). The few relatively long-term studies on mast abundance (e.g., Goodrum et al. 1971, Beck 1977) demonstrate that most mast tree species have abundant crops every 2-5 years (Fowells 1965) although a regular pattern may not exist. Most mast trees do not produce abundant crops in consecutive years (Silvertown 1980). Little information is available on interspecific patterns of mast production; e.g., Nicholas and White 1984. Downs and McQuilkin (1944) and Goodrum et al. (1971) both remarked on a tendency for mast trees of several species to have abundant crops in the same year, but this has not been rigorously tested. Given that mast crops in a region fluctuate in both space and time, they generally are not a dependable food resource (Silvertown 1980). During periods of mast shortage, mast-eating animals must either switch to alternative food resources or migrate to areas with higher mast abundance; e.g., Bock et al. 1971, Nicholas and White 1984. Population fluctuations of animals that depend on mast for food are generally greater than those of species that can switch to other food sources (Watts 1969, Smith 1986b). Here we examine patterns of fall mast abundance among tree species in 17 Missouri counties, based on long-term mast survey data collect d by the Missouri Department of Conservation. The 17 counties selected are ones in which Christmas bird counts have been conducted in Missouri, allowing direct comparisons among mast abundance patterns and winter populations of red-headed woodpeckers and blue jays over relatively small areas. Both bird species occur throughout Missouri, store mast in fall, and can occur in relatively large numbers on Christmas bird counts (Smith 1986a). Population densities of those 2 species also fluctuate from winter to winter, presumably in response to changes in mast abundance (Bock et al. 1971, Smith 1986b). We gratefully acknowledge the willingness of D. M. Christisen to share the Mo. mast data collected under his direction for many years.