The importance of winter-flowering Aloe ferox for specialist and generalist nectar-feeding birds Timothy R. Kuiper A,C , Diane L. Smith A , Milena H. L. Wolmarans A , Sara S. Jones A,B , Ross W. Forbes A , Patrick E. Hulley A and Adrian J. F. K. Craig A A Department of Zoology and Entomology, Rhodes University, PO Box 94, Grahamstown, 6140, South Africa. B Institut für Natur und Ressourcenschutz, Christian-Albrechts-Universität, Christian-Albrechts-Platz 4, Kiel, Schleswig-Holstein 24118, Germany. C Corresponding author. Email: timothykuiper@gmail.com Abstract. The abundance of consumers and the availability of resources are often linked, and birds are known to track food resources at a variety of spatial and temporal scales. This study describes the seasonal influx of nectar-feeding birds during flowering in a 51-ha stand of Aloe ferox in the Eastern Cape, South Africa, over 5 years (2008–09 and 2011–13). Bimonthly point counts of birds were conducted before (April–May), during (June–July) and after (August) flowering, which occurs during the austral winter. The abundance of nectar-feeding birds increased significantly during flowering each year, whereas monthly abundances of non-nectarivores were unrelated to flowering. Models fitted to bird count-data revealed a significant interaction between feeding guild (nectarivorous versus non-nectarivorous species) and the percentage of flowering A. ferox over the 5 years of the study, confirming that these guilds responded differently to flowering events. Malachite Sunbirds (Nectarina famosa), which are specialist nectarivores, responded consistently to flowering of A. ferox each year, despite the low sugar concentrations of A. ferox nectar. The arrival of nectar-feeding birds en masse during flowering, and the number of bird species (16) observed feeding on A. ferox nectar, suggest that this plant is an important source of nutrition for birds at a time when other food resources are likely to be scarce. Additional keywords: Nectarivore, resource tracking, seasonal flowering, sunbird, South Africa. Received 29 May 2014, accepted 18 September 2014, published online 9 February 2015 Introduction Avian populations fluctuate over a range of spatial and temporal scales (Faaborg et al. 1984; MacNally 1996; Keitt and Stanley 1998; Gill et al. 2001; Malizia 2001). Fluctuations in species diversity and individual abundances are largely driven by move- ments of birds, from small-scale movements between patches of suitable habitat to global migrations (Fraser and Stutchbury 2004; Dingle 2008). In turn, avian movements often reflect spatial and temporal patterns in the abundance of resources, a phenomenon referred to as resource tracking (García and Ortiz-Pulido 2004; Cotton 2007; Cecere et al. 2011). The importance of resource availability in determining the abundance and diversity of consumers of those resources is well established in ecological theory (Abrams 1988; Ostfeld and Keesing 2000). For those bird species that feed on nectar, flower- ing phenology often influences where individuals are found and when, particularly at smaller spatial scales (Craig and Hulley 1994; Malizia 2001; Symes et al. 2001; Cotton 2007; Las-Casas et al. 2012). The influx of nectar-feeding birds associated with mass flowering events may be particularly pro- nounced owing to the transient nature of such occurrences (Brown and Hopkins 1996; Symes et al. 2008). In South Africa, the movements of birds in both the true nectarivore guild (sunbirds (Nectariniidae) and sugarbirds (Promeropidae)) and the opportunistic nectarivore guild (e.g. weavers (Ploceidae), mousebirds (Coliidae) and bulbuls (Pycnonotidae)) can be influ- enced by the seasonal availability of nectar (Fraser et al. 1989; Underhill and Fraser 1989; Craig and Hulley 1994; Symes et al. 2001, 2008; Forbes et al. 2009). Many South African species of aloe flower during the dry winters typical of the region, represent- ing an ephemeral food resource that may attract both true and opportunistic nectarivores (Oatley and Skead 1972; Nicolson and Nepi 2005; Symes and Nicolson 2008; Symes et al. 2008; Cousins and Witkowski 2012; Symes 2012; Engelbrecht et al. 2014). Aloe ferox (Xanthorrhoeaceae, formerly Asphodelaceae) is widely distributed in eastern South Africa and is most common in the Eastern and Western Cape Provinces. Plants usually grow to 2–3 m tall (maximum 5 m) and produce a branched panicle inflorescence of 5–8 erect racemes, with flowering occurring from May to August in most of its range (Van Wyk and Smith 2003). The combination of structurally robust racemes, brightly coloured red-orange flowers, long tubular perianths, the absence of scent and long pollen to nectar distance suggest pollination by birds (Reynolds 1950; Hoffman 1988; Symes and Nicolson 2008). The production of large volumes of nectar (~180 mL per flower) with low sugar concentration (7.3–9.5% wet weight CSIRO PUBLISHING Emu http://dx.doi.org/10.1071/MU14054 Journal compilation Ó BirdLife Australia 2015 www.publish.csiro.au/journals/emu