SHORT COMMUNICATION Hoarding behavior by ship rats (Rattus rattus) in captivity and its relevance to the effectiveness of pest control operations Grant A. Morriss & Bruce Warburton & Martin L. Cross & Graham Nugent Received: 4 May 2011 /Revised: 4 July 2011 /Accepted: 11 July 2011 /Published online: 29 July 2011 # Springer-Verlag 2011 Abstract Hoarding of food items is well known among muroid rodents, but evidence for hoarding behavior among ship rats (Rattus rattus) is scant. Here, we characterize hoarding behavior in ship rats maintained in captivity after capture from the wild. After acclimatization to captivity, 40 ship rats (21 females, 19 males) were presented with baits in experiments designed to emulate a typical poison control operation for vertebrate pests in New Zealand: this involved first offering rats nontoxic cereal baits (of 2- or 6-g size) as a prefeed for three nights consecutively, followed by 6- or 12-g cereal baits laden with 0.15% 1080 on the fourth night. Seventy-eight percent of rats (31/40) hoarded food in distinct cache sites when presented with nontoxic baits although there was no significant effect of bait size or type on hoarding behavior and nor did hoarding behavior vary according to rat gender. When rats were presented with 1080-laden baits, the incidence of hoarding was reduced to 40%, due to the onset of toxicosis. This study indicates that R. rattus will show hoarding behavior analogous to other rat species when presented with an excess of cereal-based baits, at least under conditions of captivity and free from competition. This finding may have practical relevance: since 1080 is the principal toxin used against the major vertebrate pest species in New Zealand (the brushtail possum, Trichosurus vulpecula), ship rats have the potential to deplete supplies of prefeed and/or toxic baits intended for possum control. However, based on typical rat densities recorded in New Zealand native forest (c. 5 rats/ha), the degree of removal and manipulation of toxic baits observed by ship rats here is unlikely to impact adversely on the efficacy of possum control operations. Keywords Hoarding . New Zealand . Poison control . Possums . Ship rat Introduction Introduced rats (Rattus spp.) are a threat to indigenous fauna and flora in many countries. In New Zealand, three introduced species (the Norway rat, Rattus norvegicus; the Polynesian rat or kiore, Rattus exulans; and the ship rat, Rattus rattus) have been implicated in detrimentally affecting populations of native invertebrates, reptiles, and birds (Innes 2005 ; Innes et al. 2010 ). As a consequence, broadcast aerial sowing of baits containing the toxin 1080 (sodium monofluoroacetate) has become a frontline tool for large-scale rat control, while smaller local operations use static feeding stations supplied with toxic baits of several varieties (including 1080). These same techniques often have dual utility in New Zealand since many 1080 poison operations are initiated for population control against the primary introduced vertebrate pest species, the brushtail possum (Trichosurus vulpecula), which is a major threat to conservation values and a proven wildlife reservoir of bovine tuberculosis (Eason et al. 2011). Thus, high rat and possum kills are both desirable outcomes from pest control operations where the two species share habitat. However, rats are well known to hoard or cache food items for later consumption; during a poison operation, this behavior could deplete the pool of poison bait intended for the target pest and render the Communicated by C. Gortázar G. A. Morriss (*) : B. Warburton : M. L. Cross : G. Nugent Landcare Research—Manaaki Whenua, PO Box 40, Lincoln 7640, New Zealand e-mail: morrissg@landcareresearch.co.nz Eur J Wildl Res (2012) 58:483–488 DOI 10.1007/s10344-011-0562-6