SPACING BEHAVIOR OF EURASIAN THREE-TOED WOODPECKERS (PICOIDES TRIDACTYLUS) DURING THE BREEDING SEASON IN GERMANY

Auk, The, Jan 2004 by Pechacek, Peter

ABSTRACT. -Data on spacing behavior of the Eurasian Three-toed Woodpecker (Picoides tridactylus) are rare, and systematic observations are lacking. I used homing technique (>90%) and triangulation to document range use of 28 radiotagged birds in an alpine mountain forest in southeastern Germany between 1994 and 2000. Common home range of a pair (x¯ ±SE, n = 10) identified by the adaptive kernel method (95% vise distribution) during the nesting period averaged 86.4 ± 23.4 ha and varied a great deal between pairs (range 33.9-287.4 ha). Although ranges of females (69.4 ± 15.4 ha, n = 14) appeared larger than those of males (45.7 ± 10.3 ha, n = 10), the difference was not significant. Prior to nesting and during the postnesting period, both sexes used seemingly larger home ranges than during nesting (

RESUMEN. - Existen pocos datos sobre el comportamiento espacial del carpintero Picoides tridactylus y no existen observaciones sistematicas al respecta. En este estudio emplee una tecnica de ubicacion de la fuente de senales de radio (i.e. "homing"; >90%) y triangulacion para documentar el uso del espacio por parte de 28 aves marcadas con transmisores en un bosque montano alpino en el sudeste de Alemania entre 1994 y 2000. El rango de hogar comun de una pareja (x¯ ± EE, n = 10) identificado por el metodo del "kernel" adaptativo (95% de distribucion de uso) durante el periodo de anidacion promedio 86.4 ± 23.4 ha, y vario substancialmente entre parejas (rango 33.9-287.4 ha). Aunque los rangos de las hembras (69.4 ± 15.4 ha, n = 14) parecieron ser mas grandes que los de los machos (45.7 ± 10.3 ha, n = 10), la diferencia no fue significativa. Antes de anidar y en el periodo posterior a la anidacion, ambos sexos utilizaron rangos aparentemente mas grandes que en la epoca de anidacion (

MANY BIRDS LIMIT their activity to a particular area, within which they find the resources necessary for cover, foraging, and reproduction. Such an area, regularly used by an individual during a specific period of its life, is defined as a home range (Burt 1943). When a species becomes endangered, determining the size and composition of its home ranges is important for development of conservation strategies (Storch 1995, Caro 1999). Moreover, knowing about spacing behavior of endangered species is an important initial step in establishing conservation reserves. For instance, Bingham and Noon (1997) show that the most intensively used areas within the breeding home range should be identified and given priority in conservation plans (spatial requirements). Those areas are likely to provide critical habitat elements for survival and reproduction, though their importance may differ among species according to their spacing behavior.

Home-range analysis is the most common method for examining space use by individuals. Size and shape are the home-range parameters most frequently estimated. Use distribution (Hayne 1949), which describes the distribution of a bird's probability of occurrence at various points in space, has also been extensively researched. The structural cues hypothesis proposed by Smith and Shugart (1987) states that home-range size is a function of habitat features, which are correlated to expected prey productivity. Other factors, such as intraspecific competition (Krebs 1971), food abundance (Enoksson and Nilsson 1983), population density (Blackburn and Gaston 1997), or age of the territory owner (Finck 1993), also influence home-range size. Thus, a species' spacing behavior reflects the interactions of many factors, and home-range parameters by themselves do not necessarily increase the understanding of space use by birds. However, when coupled with ecological and behavioral information, the size, shape, and use distribution of home ranges become meaningful biological parameters.

Here I present results of the first major radiotracking study of the Eurasian Three-toed Wood-pecker (Picoides tridactylus) to examine its range use. This woodpecker has an expansive geographic range and inhabits boreal or alpine coniferous forests where it largely relies upon dead trees to provide abundant arthropod food. This specialization clearly conflicts with commercial forestry (Hogstad 1970, Ruge and Havelka 1993, Pechacek and Kristin 1996, Murphy and Lehnhausen 1998), and some woodpecker populations have been put at risk. It is a species of conservation concern in both the Old World (Tucker and Heath 1994, Mikusinski and Angelstam 1997) and the New World (Imbeau and Desrochers 2002).

The Eurasian Three-toed Woodpecker is extremely inconspicuous and difficult to follow in the wild, and its habitats are difficult to negotiate; thus, the species is rather poorly studied (Winkler et al. 1995, Winkler and Christie 2002). The only reliable way to obtain systematic information on the spacing behavior of the woodpecker is through radiotelemetry. Dorka (1996) reports that observation efficiency increased by 95% when woodpeckers were radiotagged. However, given the potential for early loss of transmitters, use of radiotelemetry does not guarantee collection of sufficient data. In any case, very little is known about the species' spacing behavior, and virtually nothing has been learned about seasonal changes in space-use patterns throughout its geographic range (Goggans et al. 1989, Havelka et al. 1996, Pechacek et al. 1999, Jager 2000, Jager and Pechacek 2002). Observations by Hogstad (1970, 1976, 1977, 1991) focused on niche partitioning between untagged, presumably paired woodpeckers, and are limited to the vertical scale in microhabitats (foraging trees).