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Studies of the role of testosterone (T) in birds have typically focused on sexual or aggressive behaviours of males during the breeding period, but males of nonmigratory species may invest in mate and territory long before breeding, and the influence of T in facilitating nonbreeding-season behaviours is poorly understood. We gave free-living male downy woodpeckers, Picoides pubescens, T-implants during the winter to determine whether elevated levels of T increased a male's ability to exclusively occupy territory-based resources, and whether elevated T strengthened a male's investment in an existing pair bond relationship. We also explored how a female's foraging efficiency might be affected by her mate's behaviour if he had elevated T. We found little difference between control and T-implanted males with regard to home range exclusivity. Surprisingly, male-male display rates were significantly lower in T-implanted males than in controls. Regarding male-female interactions, T-implanted males that experienced high incursion rates from other males maintained more frequent spatial association with their mate, suggesting that T facilitates male behaviours that could restrict the mate's access to other male birds. Female mates of T-males showed reduced foraging rates, but because male-female aggression was similar between treatment groups, the cause for this reduction is unknown. The results indicate that exogenous T during winter affects a variety of behaviours in male woodpeckers, and proximate influences on pair bond maintenance in winter may be a fruitful avenue for future research.Hormones have a vital influence on avian mate choice and life history. For example, male courtship, mate guarding, defence of breeding territory, the number of female mating partners per season and female choice of males depend on testosterone (T) levels in males to some degree (Moore 1984;Wingfield & Farner 1993;Enstrom et al. 1997). However, relatively few studies have examined T's contribution to facilitating male social behaviours outside the traditional breeding season, even though, in resident species, both defence of breeding territory and pairing activities may take place. In some species, T and related control mechanisms may regulate these nonbreeding-season behaviours (Wingfield et al. 1997;Hau et al. 2004). Thus, if behaviours related to defence of breeding territory and maintenance of the pair bond relationship in the nonbreeding period increase a male's fitness (and/or the fitness of his existing or future mate), increases in plasma T before the breeding period could also be advantageous.At the same time, elevated and prolonged T levels could have significant fitness costs. These may include physical wounding or depredation resulting from aggressive or otherwise conspicuous behaviours, immunosuppression and heightened energetic demands (Wingfield Buchanan et al. 2001). High male T levels might also lower the fitness of the male's mate, a possibility that is often overlooked. Increased interaction between mates cou...

Individuals in a number of bird species have the opportunity to maintain contact with their mates during nonbreeding periods. This contact may be important to synchronize the partners' reproductive cycles before breeding begins. As a first step toward exploring the function of pair bond maintenance in nonbreeding birds, I studied the behavior of three pairs of Pileated Woodpeckers (Dryocopus pileatus) and an unpaired male at roost sites during autumn. At dawn and dusk, paired individuals exchanged visual, vocal, and other acoustical signals identical to those given during the breeding season. Demonstration tapping away from a nest is reported here for the first time. The possible function of these behaviors may be related to monitoring the partner's condition and investing in the pair bond to enhance future reproductive success.

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Abstract. We investigated patterns of seasonal variation in body weight in six populations of five resident species of temperate-zone woodpeckers: Acorn Woodpecker (Melanerpes formicivorus), Red-bellied Woodpecker (M. carolinus), Red-cockaded Woodpecker (Picoides borealis), Downy Woodpecker (P. pubescens), and Great Spotted Woodpecker (Dendrocopos major). After controlling for time of day and overall body size, annual variation in body weight was small and generally not statistically significant. However, analysis revealed evidence of significant ''winter fattening,'' comparable in magnitude to other temperate-zone resident species, in three of the species. The degree of winter fattening did not correlate with either the size of the acorn crop (for the Acorn Woodpecker) or latitude, two variables potentially related to predictability of food resources. However, the smaller species exhibited significantly greater winter fattening than the larger species, as predicted by the hypothesis that energy storage should be more important for small-bodied species. Furthermore, the food-storing Acorn Woodpecker exhibited considerably less winter fattening than the nonfood-storing species, supporting the hypothesis that food storage provides an ecological alternative to winter fattening. Variación Estacional en el Peso Corporal en Cuatro Especies de Pájaros CarpinterosResumen. Investigamos los patrones estacionales de variación en el peso corporal en seis poblaciones de cinco especies residentes de pájaros carpinteros de la zona templada: Melanerpes formicivorus, M. carolinus, Picoides borealis, P. pubescens y Dendrocopos major. Tras controlar por la hora del día y el tamaño corporal general, la variación anual en el peso fue pequeña y en general no significativa estadísticamente. Sin embargo, los análisis evidenciaron que tres de las especies experimentan un ''engordamiento invernal'' comparable en magnitud al documentado para otras aves residentes de la zona templada. El grado de engordamiento invernal no se correlacionó con el tamaño de la cosecha de bellotas (para M. formicivorus) ni con la latitud, dos variables potencialmente relacionadas con la predecibilidad de los recursos alimenticios. Sin embargo, las especies de menor tamaño engordaron significativamente más que las especies de tamaño más grande, una predicción de la hipótesis que plantea que el almacenamiento de energía debería ser más importante para las especies de cuerpo pequeño. Además, M. formicivorus, una especie que almacena alimentos, exhibió un engordamiento de invierno considerablemente menor que las especies que no almacenan alimentos, lo que apoya la hipótesis de que el almacenamiento de alimento representa una alternativa ecológica al engordamiento.