The movements of black rats across the urban-bushland interface; a study using Rhodamine B

• Main Author: Weerakoon, Malith Kumara
• Format: Master Thesis
• Language: unknown
• Published: UNSW Sydney 2012
• Subjects: black rat Rattus rattus; urban-bushland interface; Rhodamine B; habitat; Australia; bait; palatability; Rattus rattus
• Online Access: https://dx.doi.org/10.26190/unsworks/15277; http://hdl.handle.net/1959.4/51657

The black rat (Rattus rattus) is a major pest species of both urban and natural environments around the world. In Australia, black rats patchily occur in bushland areas, and have a close association with humans, but their movement patterns at the urban-bushland interface remain unknown. This area represents a transition habitat which provides a jumping point to either bushland or urban areas, and understanding how rats use this area is a key step in understanding the process of naturalisation by synanthropic species. Studies of habitat use and movement often trap animals in multiple habitats to assess habitat preferences, however limited access to private residential properties in urban areas requires a less invasive technique. In my thesis, I used the bait marker Rhodamine B (RB) to assess the movements of black rats around the urban-bushland interface. Firstly, the effectiveness of RB as a palatable and reliable bait marker for black rats was investigated through a series of captive experiments. I found a palatability gradient existed for RB intake including a threshold for its palatability where intake at or above that concentration was significantly affected by a rat;s ability to freely access alternate foods. I then demonstrated that guard hairs have merit as an alternate tissue type for RB marking and detection preventing the need for animals to be sacrificed to detect RB. I then exposed rats to RB baits in residential gardens and then trapped in adjacent bushland to evaluate the extent of crossing of these habitat types. Random samples of individuals caught on the urban-bushland interface were then radio-tracked. There were a high proportion (>60%) of rats crossing the urban-bushland interface with adult females being the most likely demographic to cross, despite a trapping bias toward adult males in the bushland. Radio-tracking revealed an almost exclusive use of bushland habitat for five of six tracked rats with >95% of locations occurring in these areas. My work demonstrates the permeability of the urban-bushland interface to rats, but although most rats seem to cross, they do it only occasionally. Nevertheless, my results suggest that the control of black rats on either side of the interface will be ineffective without simultaneous control of the other.