Austral Ecology (2018) 43,25–34 Intersexual segregation in foraging microhabitat use by Magellanic Woodpeckers (Campephilus magellanicus): Seasonal and habitat effects at the world’s southernmost forests QUITERIE DURON,1* JAIME E. JIMENEZ, 1,2,3,4 PABLO M. VERGARA,5 GERARDO E. SOTO,6 MARLENE LIZAMA5 AND RICARDO ROZZI1,3,4 1Omora Ethnobotanical Park, Universidad de Magallanes, Punta Arenas, Chile (Email: kithry@ hotmail.fr), 2Department of Biological Sciences, University of North Texas, 3Department of Philosophy and Religion, University of North Texas, Denton, Texas, USA, 4Institute of Ecology and Biodiversity, Santiago, Chile, and 5Departamento de Gestion Agraria, Universidad de Santiago de Chile, Santiago, Chile, and 6Cornell Lab of Ornithology, Department of Natural Resources, Cornell University, Ithaca, New York, USA Abstract Animals facing seasonal food shortage and habitat degradation may adjust their foraging behaviour to reduce intraspecific competition. In the harsh environment of the world’s southernmost forests in the Magellanic sub-Antarctic ecoregion in Chile, we studied intersexual foraging differences in the largest South American woodpecker species, the Magellanic Woodpecker (Campephilus magellanicus). We assessed whether niche overlap between males and females decrease when food resources are less abundant or accessible, that is, during winter and in secondary forests, compared to summer and in old-growth forests, respectively. We analysed 421 foraging microhabitat observations from six males and six females during 2011 and 2012. As predicted, the amount of niche overlap between males and females decreased during winter, when provisioning is more difficult. During winter, males and females (i) used trees with different diameter at breast height (DBH); (ii) fed in trunk sections with different diameters; and (iii) fed at different heights on tree trunks or branches. Vertical niche partitioning between sexes was found in both old-growth and secondary forests. Such a niche partitioning during winter may be a seasonal strategy to avoid competition between sexes when prey resources are less abundant or accessible. Our results suggest that the conservation of this forest specialist, dimorphic and charismatic woodpecker species requires considering differences in habitat use between males and females. Key words: Campephilus magellanicus, foraging strategy, intersexual niche overlap, resource partitioning, sub- Antarctic forests. INTRODUCTION reducing intraspecific competition under resource lim- itations (Selander 1966; Slatkin 1984; Osiejuk 1994; Intersexual foraging differences leading to intraspecific Hogstad 2010). niche partitioning are widespread among vertebrates Foraging niche partitioning between sexes has been (Selander 1966; Catry et al. 2006; Ruckstuhl 2007), reported for some woodpecker species from the with these differences arising from distinct abilities of northern hemisphere, such as the White-backed both sexes to compete for food, food preferences and Woodpecker (Dendrocopos leucotos; Aulen & Lundberg nutritive needs (Catry et al. 2006; Ruckstuhl 2007). 1991) and the Eurasian three-toed Woodpecker Resource partitioning between sexes occurs at varying (Picoides tridactylus alpinus; Pechacek 2006). In these spatial scales, ranging from broad geographical parti- woodpecker species, male and females exhibit differ- tioning (e.g. Giant Petrel, Macronectes spp., Gonzalez ences in foraging behaviours and in their use of Solıs et al. 2000) to microhabitat differences (e.g. New microhabitat substrates, with male woodpeckers tend- Guinean whistlers Pachycephala spp., Freeman 2014). ing to be larger and dominant, relegating females to Morphological and behavioural differences between low-quality habitats or microhabitats (e.g., Kilham sexes contribute to foraging niche partitioning, thus 1970; Hogstad 1978; Osiejuk 1994; Pasinelli 2000; Pechacek 2006). The beneficial role of sexual niche fi *Corresponding author. partitioning for foraging ef ciency and reproductive Present address: Naleche, 23 200 Moutier-Rozeille, France success becomes more evident as the amount of food Accepted for publication July 2017. available within territories decreases (Wilson 1975; © 2017 Ecological Society of Australia doi:10.1111/aec.12531 26 Q. DURON ET AL. Austin 1976; Przybylo & Meril€a 2000). Indeed, forag- Here, we assessed intersexual foraging differences ing partitioning may improve the rate of food acquisi- in Magellanic Woodpeckers inhabiting the world’s tion for diet-specialist species like woodpeckers, for southernmost forests on Navarino Island, in the Cape which the amount of available food (e.g., saproxylic Horn Biosphere Reserve, Chile (Fig. 1; Rozzi & invertebrates) is influenced by changing environmen- Jimenez 2014). The climatic conditions of these sub- tal conditions (e.g., seasonal climate, human distur- Antarctic forests, along with a recent history of bances, wildfires). Therefore, to investigate the effects human disturbance during the 20th century, lead to of differential environmental conditions on sexual a marked variability in spatial and seasonal resource niche partitioning has a potential use on the planning availability and habitat quality for bird species (Ver- for sustainable forest management. gara & Schlatter 2006; Soto et al. 2017). The Magel- The Magellanic Woodpecker (Campephilus magellan- lanic Woodpecker is a year round resident, and a icus) is the largest woodpecker species in South Amer- charismatic species sensitive to fragmentation and ica (~36–38 cm body length, 276–363 g weight, Short loss of old-growth forest (McBride 2000; Arango 1982) and endemic to the temperate and sub-Antarctic et al. 2007; Soto et al. 2012; IUCN 2016). Habitat forests of southwestern South America from 35 to heterogeneity resulting from seasonal climatic vari- 56°S (Short 1970, Rozzi & Jimenez 2014). This species ability and anthropogenic habitat transformations lives in family groups of 2–5 members composed of a may affect foraging behaviour and space use of this breeding pair and offspring from previous years. In species, but the strength of these effects may differ old-growth forests, woodpecker territories average between males and females (e.g., see Vergara & between 40 and 60 ha, depending on season, and Schlatter 2004; Schattler & Vergara 2005; Soto et al. sometimes shift spatially among years (Ojeda & Chaz- 2012). In order to answer the question of how both arreta 2014). The breeding season lasts for ~65 days, sexes differ on their foraging niche given seasonal between mid- to late-spring and early- to mid-summer and environmental changes on resource availability, (Ojeda 2004). Parents share duties in nest excavation, we tested the following two predictions: incubation, and chick rearing. Offspring stay with par- First, we predicted that foraging partitioning ents for up to 4 years (Chazarreta et al. 2011). Even between males and females of Magellanic Wood- though the Magellanic Woodpecker is often described pecker will be greater during winter than in summer. as a forest specialist feeding mostly on large wood-bor- During the austral winter, Magellanic Woodpeckers ing larvae that are extracted by drilling live or dead tree may be exposed to food shortages in sub-Antarctic trunks and branches (Ojeda & Chazarreta 2014), they forests due to the scarcity of prey other than wood- have been reported to feed on alternative food sources, boring larvae, such as adult insects and mature fruits such as terrestrial coleoptera and hymenoptera, sap (Ojeda 2003; Ojeda & Chazarreta 2006). Our recent flowing from trees, small fruits and flowers, and even findings indicate that Magellanic Woodpeckers vertebrates like lizards and passerine chicks (McBride enlarge their territories from 0.89 km2 in the summer 2000; Ojeda 2003; Schattler & Vergara 2005). to 1.03 km2 in the winter (15% increase, n = 6 and The Magellanic Woodpecker exhibits sexual 11, respectively), likely resulting from lower levels of dimorphism, with females having a bill 12% shorter territorial behaviour and scarcity of resources. and body weight 16% lighter than males (276–312 g, Second, we predicted that foraging partitioning mean = 291.3 g, n = 6 vs. 312–363 g, mean = between male and females will be greater in sec- 338.4 g, n = 7, respectively; Short 1982; Chazarreta ondary forest than in old-growth forest. Logging and et al. 2012). Strong sexual dimorphism in plumage burning of forests by European and Chilean settlers colour also occurs: males have a scarlet-red head and on Navarino Island during the 20th century have a short-straight crest, whereas females have a black reduced the extent of old-growth forest and gener- head with red feathers at the base of the bill and a ated a mosaic of habitat patches of varying foraging long forward-curled crest. Sexual differences in bill quality (Rozzi et al. 2006; Soto et al. 2017; Fig. 1). length are associated with differences in foraging In general, trees in secondary forests have a less behaviour and prey characteristics. Chazarreta et al. advanced stage of decay and a lower abundance of (2012) reported that male woodpeckers tend to for- large wood-boring insects than in old-growth forest age on larger substrates (i.e., on the main boles of (see Vergara et al. 2017). the foraging trees) and at intermediate heights from the ground (5–10 m), whereas females forage higher towards the crown (>15 m) and on smaller sub- MATERIALS AND METHODS strates, such as branches. These sexual differences in foraging behaviour