An฀experimental฀evaluation฀of฀food฀hoarding฀by฀North฀Island฀robins฀ (Petroica฀australis฀longipes) LAUREL ALEXANDER, CATHERINE DUTHIE, JOSHUA FYFE, ZOË HAWS, SIMON HUNT, ISABEL MONTOYA, CARLOS OCHOA, ARUN SIVA, LLOYD STRINGER, JAYDEN VAN HORIK, K.C. BURNS* School of Biological Sciences, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand. kevin.burns@vuw.ac.nz Abstract We experimentally evaluated the food hoarding behaviour of North Island robins (Petroica australis longipes) at Karori Wildlife Sanctuary, Wellington. Mealworms were offered to free-ranging pairs of male and female robins to evaluate whether their food hoarding behaviour was similar to previous observations of South Island robins. We also tested theoretical predictions derived in the Northern Hemisphere, which argue that competitively subordinate birds should hoard more food than dominant birds. Results showed that the food hoarding behaviour of North Island robins was similar to South Island robins, except that North Island robins repeatedly used the same cache sites, which is rare in South Island robins. Data did not support the prediction that competitively subordinate birds hoard more food than dominant birds. Males acquired most of the mealworms offered to birds during trials, and won nearly all aggressive interactions observed between sexes. Therefore, males appeared to be competitively dominant to females in winter. However, males stored over five times as many mealworms as females, which is opposite to theoretical predictions. We interpret the reluctance of females to cache food as a strategy to avoid food loss to competitively dominant males. Alexander, L.; Duthie, C.; Fyfe, J.; Haws, Z.; Hunt, S.; Montoya, I.; Ochoa, C.; Siva, A.; Stringer, L.; Van Horik, J.; Burns, K.C. 2005. An experimental evaluation of food hoarding by North Island robins (Petroica australis longipes). Notornis 52(3): 138-142. Keywords: Food hoarding; competition; experiment; North Island robin; Petroica australis INTRODUCTION Recent studies of food hoarding behaviour in birds have generated important insights into avian cognition (Krebs et al. 1996; Emery & Clayton 2001; Milius 2004), social dynamics (Heinrich & Pepper 1998; Pravosudov et al. 1999; Vanderwall & Jenkins 2003) and foraging behaviour (Pravosudov & Grubb 1998; Brodin 2001; Smith et al. 2002). Although some southern hemisphere birds hoard food (e.g. bowerbirds (Ptilinorhynchidae); Pruett- Jones & Pruett-Jones 1985), nearly all previous work has come from the northern hemisphere. Our knowledge of food hoarding in New Zealand birds is restricted to a single study on South Island robins (Petroica a. australis) (Powlesland 1980). Theoretical work predicts that competitively subordinate birds should hoard more food than dominant birds to offset losses resulting from cache pilfering (Brodin et al. 2001). Empirical tests of this prediction have been conducted mostly on tits (Paridae) and jays (Corvidae) in aviaries, and their results are mixed (see Lundborg & Brodin 2003 for a recent review). Additional tests on species with different life history traits may help elucidate the factors responsible for the conflicting results of the aviary tests. Like many bird species endemic to isolated islands, New Zealand’s robins lack pronounced anti-predatory behaviours (see Carlquist 1965). They are fearless of humans and wild birds will consume food offered to them by hand (Armstrong et al. 2000). Although this attribute enhances their vulnerability to predation by introduced mammals, it might also generate a unique opportunity to test food-hoarding theory. In winter 2003, we conducted a field experiment on free-ranging North Island robins (Petroica australis longipipes) to evaluate their food-hoarding behaviour. We offered mealworms (Tenebrio molitor) larvae to pairs of robins on their winter territories to evaluate whether: 1. their food-hoarding behaviour was similar to that of South Island robins; 2. females were competitively subordinate to males; and 3. females hoard more food than males. METHODS The experiment was conducted in the Karori Wildlife Sanctuary (KWS: 41° 18’ S, 174° 44’ E), a 2.5 km 2 catchment of regenerating forest within Wellington city. The area experiences a mild, temperate climate, with annual rainfall averaging Notornis, 2005, Vol. 52: 138-142 0029-4470 © The Ornithological Society of New Zealand, Inc. 2005 138 Received 1 November 2004; revised 10 May 2005; accepted 22 May 2005