Contributions to Zoology, 82 (2) – 2013E. Johanna Rode; K. Anne-Isola Nekaris; Matthias Markolf; Susanne Schliehe-Diecks; Melanie Seiler; Ute Radespiel; Christoph Schwitzer: Social organisation of the northern giant mouse lemur Mirza zaza in Sahamalaza, north western Madagascar, inferred from nest group composition and genetic relatedness

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Introduction

Security offered by shelters is an important aspect in the survival and reproduction of many small mammals, including strepsirrhine primates (Terborgh and Janson, 1986; Anderson, 1998; Kappeler, 1998). Types of shelters include tree holes or cavities, dense vegetation tangles and self-constructed or abandoned leaf nests (Bearder et al., 2003). Shelters provide protection against predators, especially when raising young, and protect against environmental conditions such as temperature changes (Aquino and Encarnación, 1986; Anderson, 1998; Kappeler, 1998; Perret, 1998; Schmid, 1998; Biebouw et al., 2009). Although tree holes are generally regarded as high-quality shelters (Radespiel et al., 1998; Schmid, 1998), constructing leaf nests has a high adaptive potential due to independence from pre-formed tree cavities and possible immediate and flexible responses to environmental changes (Thorén et al., 2010). While some taxa like diurnal ruffed lemurs (Varecia variegata (Kerr, 1792)) only use nests in the breeding season to hide their altricial infants (Kappeler, 1998), many adult nocturnal strepsirrhines spend the day in leaf nests, including Galagoides, Galago and Otolemur (Bearder and Doyle, 1974; Bearder et al., 2003), Microcebus ravelobensis Zimmermann et al., 1998 (Weidt et al., 2004; Thorén et al., 2010), M. murinus (J. F. Miller, 1777) (Radespiel et al., 1998), Mirza coquereli (A. Grandidier, 1867) (Sarikaya and Kappeler, 1997), Cheirogaleus major É. Geoffroy, 1812 (Wright and Martin, 1995) and Daubentonia ma­dagascariensis (Gmelin, 1788) (Sterling 1993; Ancrenaz et al., 1994). Type and location of nests probably have a crucial impact on the survival and reproduction of nest-using species (Wells et al., 2006). Information about nests and sleeping trees could assist in conservation planning, for example to inform restoration of habitat or develop indirect census techniques (Plumptre and Reynolds, 1997; Blom et al., 2001; Johnson et al., 2004).

Mirza zaza Kappeler and Roos in Kappeler et al., 2005 is one of at least eight nocturnal lemur species in Madagascar that uses arboreal leaf nests as shelters during the day (Kappeler, 1998; Kappeler et al., 2005; Thorén et al., 2010). The species is classified as Vulnerable on the IUCN Red List due to its restricted and highly fragmented distribution (Rode et al., 2011). Because M. zaza occurs in only one protected area and due to on-going threats to remaining and fragmented forests where it occurs (Schwitzer and Lork, 2004; Schwitzer et al., 2007), information on its ecological needs is urgently required to design conservation measures.

In contrast to M. coquereli, where males and females have never been observed to share nests (Kappeler, 1997), M. zaza on the Ambato Peninsula, near Ambanja, was observed to sleep in self-constructed, spherical leaf nests with two to eight individuals including several adult males (Kappeler et al., 2005). Large nests can become unstable and disintegrate with time (Lindenmayer et al., 2008), which sets an upper limit for nest size. Wells et al. (2006) have shown that support and location are important conditions for a good nest; stability and texture of branches must be appropriate, and materials for construction must be available. The height and position of nests have an impact on thermoregulation including exposure to sun and rain or humidity (Bearder et al., 2003). The nests of M. coquereli in Kirindy were built a few meters below the top of trees of the genus Securinega (family Euphorbiaceae) (Sarikaya and Kappeler, 1997) while Pages (1980) reported heights of 2-10 m in trees that did not shed their leaves (Euphorbiaceae) and were covered in lianas.

Sleeping in nest groups can have energetic advantages. Social constraints and the need for some small animals to enter torpor can limit the maximum number of animals sleeping together, as has been shown for Microcebus murinus, where such constraints limit group size to two to four animals (Perret, 1998). Nest associations can give an indication about the social organization and mating system of the species (Kappeler and van Schaik, 2002). Most nocturnal strepsirrhines sleep in small groups including female kin and offspring (Nash and Harcourt, 1986; Radespiel, 2006), with several males sleeping rarely together (Pullen et al., 2000; Bearder et al., 2003; Eberle and Kappeler, 2006; but see Loris lydekkerianus lydekkerianus Cabrera, 1908; Nekaris, 2003). Morphological and behavioural data suggest a promiscuous mating system for Mirza zaza (Kappeler et al. 2005; Rode, 2010); information about nest use could sharpen this picture.

With information about the rarity of M. zaza becoming increasingly available, we aim to answer two questions regarding their nesting behaviour in relation to potential habitat management for their conservation. First, what are the height and position of nests of M. zaza? Second, which nest site characteristics are selected by M. zaza? Finally, we aim to provide preliminary data on their social organisation by examining nest fidelity as well as the composition and stability of nest groups by using behavioural and genetic data. We test several hypotheses regarding the composition of mixed-sex groups (Radespiel et al., 2009): rearing groups: comprise females and their immature offspring; family groups: include both parents and their immature offspring; mating groups: comprise potential mates (unrelated males and females); social groups: include unrelated and/or related individuals, offering advantages of group living to members with respect to environmental challenges (low temperature, predation risk).