Red-cockaded woodpecker nutritional status in relation to habitat: Evidence from ptilochronology and body mass
Sexual divergence in foraging behavior exhibited by red-cockaded woodpeckers (Picoides borealis) should reduce intersexual competition for foraging sites. Males tend to forage at greater heights and on smaller stem diameters than females. It is well known that red-cockaded woodpeckers have an aversion to a well-developed stratum of midstory vegetation. Foraging areas with increased midstory vegetation may cause females to increase their foraging height, thus bringing them into greater competition with males. It has been suggested that female red-cockaded woodpeckers, to a greater extent than males, may suffer nutritional stress due to a reduction in foraging niche under certain conditions. In eastern Texas, we measured growth bars of red-cockaded woodpecker rectrices using the techniques of ptilochronology to obtain an index of nutritional status of individual woodpeckers during the period of feather growth. Total rectrix length and body mass were also obtained as additional measures of nutritional status. Data were acquired from 2 forest types determined by the dominant pine species in the overstory: (1) longleaf pine (Pinus palustris) habitat which is relatively devoid of well-developed midstory vegetation, and (2) mixed loblolly pine (P. taeda)-shortleaf pine (P. echinata) habitat where midstory vegetation was generally well-developed. We compared width of 6 growth bars, rectrix length, and body mass between birds occupying these 2 pine habitats using 2-factor analyses of variance with pine habitat and molt year as the main effects. These were followed by a least significant-difference test. Adult males and adult females were tested separately. Width of 6 growth bars and rectrix length were similar for adult males in longleaf pine and loblolly-shortleaf pine habitats, but body mass was greater in the latter. Width of 6 growth bars, rectrix length, and body mass were all greater for adult females in loblolly-shortleaf pine habitat than in longleaf pine habitat. Our results indicate that red-cockaded woodpeckers are generally more nutritionally fit in loblolly-shortleaf pine than in longleaf pine habitat in eastern Texas despite more adverse midstory conditions in the former. They also suggest adult females may experience greater nutritional stress than adult males.
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