Behavioural ecology of New Zealand invasive rodents (Rattus norvegicus and Mus musculus) : implications for rodent control : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Auckland, New Zealand
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Date
2013
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Massey University
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Abstract
Biological invasions are natural phenomena that have occurred throughout the natural history
of earth. The highly negative context of the term biological invasion is associated with the
fact that many modern invasive processes are anthropogenically driven. Indeed, human
affiliated invasions are among the primary drivers of the current biodiversity crises. Murid
rodents (Rodentia: Muridea) of the genus Rattus and Mus have become among the worst
vertebrate invasive species and apart from man are the most widespread mammals on earth.
Invasive rodents have severe and negative effects on human health, agricultural systems, and
natural environments. The practice of rodent control is extensive and substantial attempts are
made to decrease rodents’ severe impacts on the environment. However, although these
attempts are largely successful, there are still issues in the control of invasive rodents and
new methodologies, whether at a macro or micro scale are actively pursued.
Behavioural conservation attempts to understand and improve conservation processes
and practices through the study of animal behaviour. Indeed, it is becoming increasingly
apparent that the behaviour of animals can be a strong tool for conservation. The control of
invasive species has the goal of reducing predatory or competition pressure on species of
conservation concern and advocates for behavioural conservation acknowledge the
importance of behavioural studies of invasive species that can directly benefit or inform
control measures. In this thesis, I explore several aspects of behavioural ecology in the
Norway rat R. norvegicus and the house mouse, M. musculus, with the overarching aim of
informing and improving rodent control.
I conducted a series of laboratory and field experiments focused on rodent behaviour
and pest control. 1) I tested whether laboratory rats can act as effective lures for wild Norway
rats and hence overcome the problem of rats avoiding food baits. This field experiment was
based on the highly social behaviour exhibited by this species. I found that live traps
containing live lures were significantly more effective than those with food baits at capturing
wild Norway rats. In a second series of tests, I found that live lures were more efficient than
food baits at attracting rats to kill traps. A study of radio-collared rats released onto a rat-free
island produced inconclusive but promising results on the potential of live lures to be used to
control incursions. I suggest that the use of laboratory rats as lures should be considered as an
additional tool for use in future pest control management plans for invasive Norway rats. 2)
I used Y-maze laboratory experiments to examine the attractiveness of urine from mice fed
high and low protein diets to male and female wild mice, whether the protein content of the
diet of mice affected their response and the strength of attraction of wild mice towards wild
and laboratory live lure conspecifics of the opposite sex. I found that mice preferred to spend
more time close to urine from donors that had eaten a high protein diet, that mouse strain did
not affected conspecific attraction and that males were more active than females toward the
urine of the opposite sex. These results may have implications for improving mouse capture
and control. 3) I assessed the impacts of mammalian odours (specific direct cues of predation
or competition) and illumination intensity (a general indirect cue of predation) on the
foraging of free-ranging mice that are naïve to mammalian predators, using feeding trials in
the field. Here I found that phases of the moon, but not odour, had significant effects on
mouse foraging behaviour. I suggest that repeating the study over multiple lunar cycles is
required to confirm this influence and, if confirmed, recommend coordinating management
efforts according to the phases of the moon to improve mouse bait take and reduce bait
wastage. 4) I tested for the responces of rat-naïve mice to scent cues from rats, which are
competitors and potential predators in laboratory experiments, in a Y-maze apparatus. Mice
behaviours revealed unexpected differences in male and female responces to rat scent. Male
mice showed preference to control over rat scented food trays, while females were
indiference in their preferation or even prefered rat scented food trays over control ones.
These sex-based differences can suggest that males and females might be under different
evolutionary pressures in regard to novel scents. 5) I looked at macronutrient selection in
wild caught mice, under controlled laboratory conditions. I found that mice consumed more
of diets with a high carbohydrate/protein ratio, but were highly generalist and opportunistic
feeders, in general prioritising energy over macronutrients. These results demonstrate that the
pattern of macronutrient selection is sensitive to ecological circumstances, and associates an
opportunistic strategy with successful invasion by a small mammal in a temperate
environment.
The understanding and improvement of conservation practices directly through the
study of animal behavioural processes is an emerging and rapidly growing science, but
relatively little attention is given to the benefits that we can draw from incorporating and
understanding of invasive species behaviour into their control. To maintain an effective and
continuous control of invasive species, managers need comprehensive knowledge of the
behaviour of the species they target. This can be achieved only through targeted behavioural
research of invasive species that is directed at improving pest control. In this thesis I have
attempted to do just this.
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Keywords
Rats, Laboratory rats, Rattus norvegicus, Rat control, Biological control of rats, Rat behaviour, Mus musculus, Mice, Mouse behaviour, Mouse control, Biological control of mice, Behavioural ecology