Nesting Phenology and Competition for Nest Sites among Red-Headed and Red-Bellied Woodpeckers and European Starlings

-I observed 96 pairs of Red-bellied Woodpeckers (Melanerpes carolinus) and 105 pairs of Red-headed Woodpeckers (Melanerpes erythrocephalus) during three breeding seasons in urban and rural areas in Oktibbeha County, Mississippi. European Starlings (Sturnus vulgaris) and Red-bellied Woodpeckers initiated nests in late March and early April; Red-headed Woodpeckers nested during the first week of May. Most competition for freshly excavated nest sites was between starlings and Red-bellied Woodpeckers. Fifty-two percent of Redbellied Woodpecker nest cavities and 7% of Red-headed Woodpecker nest cavities were usurped by starlings. Differences in nest-site parameters of the woodpecker species appeared to influence starling choice of cavities. Pairs of Red-bellied Woodpeckers unable to avoid starling competition suffered apparent reductions in fecundity. Ultimately, pairs able to avoid starling competition in March and April should be at a selective advantage. Received 5 April 1988; accepted 12 October 1988. AN a priori assumption for interspecific competition is that a reduction in fitness occurs in individuals adversely affected (Roughgarden 1979). Studies on interspecific competition in birds demonstrate such reductions in fecundity (Dhondt and Eyckerman 1980, Hogstedt 1980, Minot 1981, Garcia 1983, Minot and Perrins 1986, Gustafsson 1987). Numerous authors report interactions between European Starlings (Sturnus vulgaris) and other cavity-nesting species (Wood 1924, Shelley 1935, Howell 1943, Kilham 1958, Polder 1963, Zeleny 1969, Reiler 1972, Troetschler 1976, Ingold and Ingold 1984), but few attempt to document competition using fitness as a measure. The fecundity of cavity-nesting birds is limited by the availability of nest sites (von Haartman 1957, Hilden 1965, Scott 1979, Mannan et al. 1980). Troetschler (1970, 1976) found that starlings successfully usurped Acorn Woodpecker (Melanerpes formicivorus) nest cavities which increased starling populations. Troetschler (1976) concluded that because Acorn Woodpeckers responded to starling competition by excavating more cavities or delaying nesting, their fecundity was not adversely affected and local populations remained stable. Conversely, van Balen et al. (1982) and Nilsson (1984) found reductions in the breeding success of both Great Tits (Parus major) and Nuthatches (Sitta europaea) from starling competition for nest cavities. Red-bellied Woodpeckers (M. carolinus) and Red-headed Woodpeckers (M. erythrocephalus) are two common primary cavity-nesting species broadly sympatric with starlings in eastern North America. In the southeastern United States, starlings and Red-bellied Woodpeckers (Red-bellies) generally initiate nesting in late March and early April, and Red-headed Woodpeckers (Red-heads) begin in early May (Bent 1939, Imhof 1976, Dakin 1984). Double-broodedness is common in the three species (Coues 1903, Bent 1939, Short 1982, Dakin 1984, Smith and Layne 1986, Ingold 1987). Both woodpecker species lose cavities to starlings (Kilham 1958, Zeleny 1969, Reller 1972, Jackson 1976, Short 1979), but the short breeding season of starlings and the tendency for later nesting by Red-heads, coupled with their aggressive nature, could make them less vulnerable to starling competition. I quantified the nesting phenology of the three species, and identified the degree of phenological overlap and timing of potential competition for nest sites among them. I also compared woodpecker nest-site parameters and the proportion of Red-belly nest cavities vs. Red-head nest cavities usurped by starlings. I discuss whether differences in proportions are related to nesting phenology or nest-site parameters of the woodpeckers, and whether a relationship exists between the timing of reproductive ef209 The Auk 106: 209-217. April 1989 This content downloaded from 157.55.39.80 on Fri, 22 Apr 2016 05:46:58 UTC All use subject to http://about.jstor.org/terms 210 DANNY J. INGOLD [Auk, Vol. 106 forts in Red-bellies and Red-heads and their fecundity. Interspecific competition between starlings and native North American woodpeckers apparently reduces woodpecker fecundity. STUDY AREA AND METHODS From 15 March through 5 September 1985-1987, active Red-bellied and Red-headed woodpecker nest sites were located on the Mississippi State University (MSU) campus, the MSU south farm, and in the city of Starkville. The study area covered ca. 4,200 ha in Oktibbeha County, Mississippi. Starling boxes within this area from a previous study (Dakin 1984) were monitored, and other active starling nests were located in the study area. The campus and city are characterized by scattered hardwoods and pines surrounded by lawns, roads, buildings, and abandoned lots. The south farm consists primarily of pastures and hay meadows with scattered hardwoods and large snags. Because starlings and Red-bellies initiated nesting concurrently, pairs of Red-bellies were categorized as either competitors or controls (competition-free). Pairs were considered controls if starlings were not detected at or near their nest sites (a circular area of ca. 0.5 ha around the cavity tree) throughout breeding. Although such a method of categorization did not preclude that some control birds would encounter starlings, the criteria used in defining such pairs made it unlikely. Each active woodpecker nest was observed for at least 30 min each week between 0700 and 1900 to determine status and detect overt interactions between starlings and woodpeckers. I observed cavities where starlings were present up to 4 h/week. An interaction was recorded when two species, within sight of each other, responded mutually. Acknowledgments included vocalizations, aggressive pursuit flights, or attacks at the nest cavity. Nest sites that could be reached were climbed each week to confirm occupancy and nest status.