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The Ecology of Brown Rats (
Rattus norvegicus) on Rum
COMMERCIAL IN CONFIDENCE
Statement of Requirements
SNH-SEPA Magnus Magnusson PhD Studentships
2012-2015
The Ecology of Brown Rats (Rattus norvegicus) on Rum
CONTENTS
1) Purpose of the work……………………………………………………………………… ........... 3
2) Background ...................................................................................................................... 2
3) Approaches ..................................................................................................................... 4
4) Draft Methodology ........................................................................................................... 5
5) Reporting ......................................................................................................................... 5
6) Contract management ....................................................................................................... 9
7) Key Stages........................................................................................................................ 9
8) Outputs and outcomes …………………………………………………………………………..10
9) Payments ........................................................................................................................ 11
10) Health & Safety ............................................................................................................. 12
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The Ecology of Brown Rats (
Rattus norvegicus) on Rum
Specification of Requirements
1) Purpose of the work
The work described here is a PhD project under the Magnus Magnusson SNH-SEPA PhD
Studentship Programme, awarded in 2011/2012 (and starting in October 2012). The
primary purpose of the work is to describe the ecology of brown rats (an invasive non-native
species) on the Inner Hebridean island of Rum. The reason for this is that the globally
important Manx shearwater population currently coexists with the brown rat population, and
so the reasons for this need to be understood given that rats and petrels rarely coexist on
seabird islands.
2) Background
The Manx shearwater population on Rum has been studied, albeit intermittently, for some
50+ years. Some data has been gathered on breeding productivity up till 1994, after which
a long running study has been undertaken, largely by volunteers & an external contractor.
Hence SNH now hold a long running, though incomplete data set on breeding productivity
from the colony on Rum. In recent years the population’s productivity has declined and
there is a possibility that this has been caused by increased predation from resident brown
rats on Rum. Manx shearwaters are only vulnerable to predation for part of the year. Manx
shearwaters return to Rum in late March and early April. Egg laying commences in May
though there is some variation between years in the peak laying date, and hence fledging
dates also vary.
Rats are thought to be responsible for numerous seabird extirpations and global population
declines through predation on eggs, chicks and adult birds (Atkinson, 1985). Jones et al.
(2008) examined 115 independently reported rat-seabird interactions on 61 islands or island
chains, comprising 75 species of seabirds in 10 different families. In general, the presence
of rats was associated with negative trends in seabird abundance; however, the overall
effect was relatively weak. This rather surprising result was explained by a more detailed
analysis of the data that suggested that not all seabird groups were equally affected; some
seabird families appeared to be much more vulnerable than others to the effects of invasive
rats. Crevice or burrow nesting species (such as Hydrobatids and Alcids) were
disproportionately affected by the presence of rats; larger, ground-nesting species such as
albatrosses (Diomedeidae) and Larids experienced the lowest population impacts. The
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The Ecology of Brown Rats (
Rattus norvegicus) on Rum
species of rat involved, and geographical variables, particularly latitude, were also identified
as important factors.
More recently, Ruffino et al. (2009) proposed that the coexistence of black rats
Rattus rattus
and seabirds on many Mediterranean islands was facilitated by biogeographical factors that
created intra-island refuges for seabirds. In particular, the life-history traits of rats may
exclude them from areas that do not have sufficient resources to continuously support rat
populations, and they may not be able to occupy seasonally areas that are protected by
their remoteness or terrain. Hence the current view that rats always should be removed to
protect seabird colonies is too simplistic; some islands may provide refuge for seabirds in
areas that rats cannot access or occupy for extended periods. A better understanding of the
ecological processes underlying predation risk may allow refinement of seabird
conservation strategies.
For example, it has been previously recognised that Norway rats are present within the
internationally important Manx shearwater colonies on the island of Rum. This has led to
concerns that the shearwater colonies may be under threat from predation by rats. Recent
work, however, has suggested that Norway rat abundance within the shearwater colonies
on Rum is low, and therefore predation risk is also likely to be low (Lambert and Cain,
2011). It is possible that the colonies are protected by their high altitude and remoteness
(mainly above the 450m contour), but also possible that rat abundance varies over time;
recent severe winters could have temporarily suppressed rodent density.
Given widespread reporting of the catastrophic impacts of rats on breeding petrels and
shearwaters, with, in some cases, colony (or even occasionally species) extinction (see, for
example, Atkinson, 1985; Jones at al, 2008, Brooke et al, 2010, and Hilton and Cuthbert,
2010), it is interesting that the Rum Manx shearwater colony appears to co-exist with brown
rats. The implication of this for the conservation of other petrel and shearwater colonies in
Scotland is that a better understanding is needed of the conditions that permit (or prevent)
co-existence with rats.
Very little is known about the ecology of Norway rats on Rum, or indeed in island
environments in general. In particular, it is unclear what factors determine overwinter
survival of rats in the Manx shearwater colonies, when the birds are absent. One of the
objectives of this project will be to determine rat diet (via analysis of stomach contents)
during the winter months. Remains of native wood mice
Apodemus sylvaticus have been
found in rat stomach contents on Rum in the spring and summer (Bell, 2008), but it is not
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The Ecology of Brown Rats (
Rattus norvegicus) on Rum
known whether this represents rat predation of live wood mice, or if rats are consuming as
carrion mice killed during trapping in the shearwater colonies. Possible inter-relationships
between the Norway rats and the wood mice on the island will be investigated during this
project, with the aim of determining to what extent, if any, predation on wood mice may be
sustaining rat populations on the island.
One of the factors which will be considered in this project is the possible impact of future
climate change on the island’s rat populations, both directly (via, for example, changes in
the vegetation food supply) and indirectly, as a result of changes in other aspects of the
management of Rum as a National Nature Reserve.
Climate trends over the past 40 years show an average annual temperature increase of
1.04°C in West Scotland, along with a reduction of over 40% in the number of days of snow
cover (Barnett et al, 2006). Increased rodent survival has been linked to warmer climate
conditions in a number of studies (for example, Bengston, 1989) and it is likely that an
increase in growing degree days will provide a wider window of opportunity for rats on Rum.
Without basic knowledge of diet, population dynamics, movement patterns and home range
of rats on Rum, however, the long-term risk to species such as Manx shearwaters, and to
seabird populations on similar islands, cannot properly be assessed. The aim of the current
project is therefore to gather key ecological data through study of Norway rat populations on
Rum, in order to inform future management policy for this globally important Manx
shearwater breeding site.
3) Objectives
The key objective for this work is to gain a thorough understanding of the ecology of the
brown rat on Rum, in particular:
• Distribution and abundance of the Norway rat on Rum
• Population dynamics
• Movement patterns and home range size
• Habitat and food preferences
• Key factors determining over-winter survival of rats and, in particular, over-
winter survival at higher altitudes in the manx shearwater
Puffinus puffinus breeding colonies on Rum
4) Methodology
The approach to this work will be set out in tenders, and confirmed at the inception of the
project. SNH envisage that it will include the following steps.
Home range size and movement patterns
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The Ecology of Brown Rats (
Rattus norvegicus) on Rum
Much is known about the ecology of individual rats in mainland contexts, in both urban and
rural habitats. These studies have helped to refine rodent control strategies, through the
development of control methods that are adapted to the foraging behaviour and movement
patterns of rats (Cowan, Quy, & Lambert 2003; Meerburg et al. 2004;Quy, Cowan, &
Lambert 2003). However, almost nothing is known about the ecology of rats in island
contexts, particularly in northern latitudes. This has hindered the development of
conservation programmes that aim to protect seabird colonies from rodent interference.
It is always assumed for example, that where rats occur, seabird colonies are under threat
from predation. However this may not always be the case; some seabird colonies may be
able to persist on islands where rats are present through the existence of intra-island
refuges (Ruffino et al. 2009).
It is likely that many seabird colonies do not provide sufficient resources to sustain rat
populations outside the seabird breeding season, and may be so remote that they are not
subject to regular incursions from rats, particularly if they are surrounded by areas of habitat
that do not provide sufficient resources. It may be possible to use localised control in these
areas to manage rat populations, even if it is not considered practical to remove rats from
an entire island. This approach may be particularly suitable for Rum.
This strategy, however, would require a more detailed understanding of Norway rat
movement patterns in island contexts. In order to provide these data, it is proposed that 5-
10 rats in three study sites on Rum (village, coast, shearwater colonies) will be caught using
live-capture traps, fitted with radio-transmitters, and then released. The movement patterns
of these rats will be determined, by regularly locating the tagged animals, for up to six
months after release.
During the first field season (Year One) of this study, a larger sample (upwards of 50) of
live-trapped animals from the village will be fitted with PIT tags (in compliance with current
licensing requirements for this technique). Inserted subcutaneously, these tags provide a
life-long means of identification of individual animals in a population. Whilst the use of PIT
tags does not provide data on movement patterns, this technique does offer a greater
likelihood of detection of migration of individual animals between the village and other areas
of the island, particularly the shearwater breeding colony.
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The Ecology of Brown Rats (
Rattus norvegicus) on Rum
Calibration of census methods and dietary analysis
Several methods for assessing rodent abundance are available, including index trapping
and use of non-toxic monitoring baits (census baiting). However, behavioural variation
between populations, and variation in the availability of alternative food over time, can
confound direct census methods, particularly indices based on trapping (Taylor, Quy, &
Gurnell 1981); indirect census methods that measure changes in levels of rodent activity
(such as tracking plates) are therefore considered more reliable (Quy, Cowan, & Swinney
1993).
An index of activity can be calculated by using tracking tiles that record rodent footprints; by
standardising the method (tile size, positioning and spacing) the method can be used to
compare reliably levels of rodent activity between sites and over time. This approach was
used to generate activity indices for populations of rats living on farms; by subsequently
removing all of the rats by intensive trapping, and confirming complete removal of rats by
census baiting, the activity indices could be calibrated against known population sizes (Quy,
Cowan, & Swinney 1993). By using this calibration curve, an estimate of the rat population
size at other farms could be calculated from the activity index generated by the use of
carbon coated tracking tiles.
It is unclear, however, whether the calibration curve would need to be adjusted for sites that
are substantially different to those used in the calibration study and it is possible that
differences in the density of rat populations between different habitats will necessitate
adjustment of the calibration curve in order to generate accurate population estimates.
It is likely that many island habitats would support low density rat populations because of
the lower availability and wider distribution of food resources. We propose that the tracking
plate technique is calibrated for low-density populations typically found in island contexts.
Tracking plates will be deployed at study sites in 10 or more areas where rat density is likely
to be low (heathland habitats, shearwater colonies) using the published methodology;
carbon-coated tracking plates measuring 200mm x 100mm will be deployed at a density of
400 plates ha-1 to encompass the extent of rodent signs recorded in an initial survey of each
site, or in 0.25 ha squares (100 tracking plates) if no obvious signs of rodent activity are
recorded. Each plate will be scored according to the percentage of the plate marked by rat
footprints (0-25% = 1, 26-95%=2, 96-100% =3); the sum of the scores gives an index of
activity. Marked plates will be replaced or re-painted for three consecutive days; the
average activity index for three nights will then be calculated.
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The Ecology of Brown Rats (
Rattus norvegicus) on Rum
Snap traps will then be deployed to remove all rats from each study site; the removal of rats
will subsequently be confirmed by the use of non-toxic census baits. A calibration curve will
then be generated by plotting the activity indices against known population sizes. Trapped
rats will be examined
post-mortem to determine stomach contents and collect biological
material for future analysis (e.g. genomics; although it is envisaged that this will not form
part of the current proposal). This procedure will be repeated at other similar study sites in
ten or more areas using another commonly used method for obtaining estimates of rat
abundance (for example non-toxic monitoring baits, such as chocolate impregnated wax
blocks), in order to determine the most suitable census method for rats in these contexts.
Distribution and abundance of Norway rats on Rum
In order to gain a greater understanding of the abundance and distribution of Norway rats
on Rum, and how these vary seasonally, an island-wide survey of rat activity will be
undertaken. The results from work in the first field season will be used to select the most
appropriate survey method, which will then be used in an island-wide survey of rat
abundance and distribution using a combination of a stratified random deployment of grid
squares, and trapping (using Snap traps) along 500m line transects.
References:
Atkinson, I. A. E., 1985. The spread of commensal species of
Rattus to oceanic islands and
their effect on island avifaunas. In:
Conservation of island birds, ed. P. J. Moors,
International Council for Bird Preservation, Cambridge, United Kingdom.
Barnett, C., Hossell, J., Perry, M., Proctoer, C., and Hughes, G. 2006.
A handbook of
climate trends across Scotland. SNIFFER Project CC03; Scotland and Northern
Ireland Forum for Environmental Research, Edinburgh, United Kingdom.
Bell, E. 2008. Monitoring of rat abundance at Manx shearwater colony on Isle of Rum.
Report from Wildlife Management International Ltd. to SNH. WMIL, Blenheim, New
Zealand.
Bengston, S.A., Nilsson, A. and Rundgren, S. 1989. Population structure and dynamics of
wood mouse
Apodemus sylvaticus in Iceland.
Holarctic Ecology, 12 (4), 351-368
Brooke, M. de L., O’Connell, T.C., Wingate, D., Madeiros, J., Hilton, G.M., and Ratcliffe, N.
2010.
Potential for rat predation to cause decline of the globally threatened Henderson petrel
Pterodroma atrata: evidence from the field, stable isotopes and population modelling.
Endangered Species Research Vol. 11 (1), 47-59
Brown, P.M.J.
, Thomas, C., Lombaert, E., Jeffries, D.L., Estoup, A. and Lawson Handley,
L.J. 2011. The global spread of
Harmonia axyridis: distribution, dispersal and routes of
invasion.
BioControl 56 (4): 623-642.
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The Ecology of Brown Rats (
Rattus norvegicus) on Rum
Courchamp, F., Chapuis, J.L., and Pascal, M. 2003. Mammal invaders on islands: impact,
control and control impact.
Biological Reviews 78 (3), 347-383
Cowan, D. P., Quy, R. J., Lambert, M. S., 2003. Ecological perspectives on the
management of commensal rodents. In: G. R. Singleton et al., (eds)
Rats, mice and
people: rodent biology and management. Australian Centre for International
Agricultural Research Monograph, Canberra.
Hilton, G.M., and Cuthbert, R.J. 2010 The catastrophic impact of invasive mammalian
predators on birds of the UK Overseas Territories: a review and synthesis.
Ibis 152
(3), 443-458
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The Ecology of Brown Rats (
Rattus norvegicus) on Rum
Contract Details
5) Reporting
Interim (annual) reports will be required, along with a final copy of the thesis.
• One bound copies of the thesis is to be supplied. A copy should also be supplied on
CD in Word for Windows format.
• The student should also lodge copies of relevant data files with SNH. Data files
should be in a format compatible with MS Office Systems and/or ArcGIS format (if
GIS is used).
• The final report is to be emailed or sent on CD in Word for Windows format directly
to the Nominated Officer by the University (Anglia Ruskin University), unless
otherwise agreed.
6) Contract management
The SNH Nominated Officer for this contract is:
Dr. Andrew Douse
Policy & Advice Manager, Ornithology
Scottish Natural Heritage
Great Glen House
Leachkin Road
Inverness
IV3 8NW
Telephone:
01463 725241
E-mail:
xxxx.xxxxx@xxx.xxx.xx
7) Key Stages
The key stages of the project are detailed below with the indicative timetable to be agreed
between the University, the Food & Environment Research Agency (Fera), and the SNH
Nominated Officer. Meetings may be held at other locations or by video conference or
teleconference as agreed by all parties.
Inception meeting
October 2012
Possibly on Rum
Interim report
March 2013
Meeting in Cambridge or
Interim report meeting
March 2013
York
Interim report
September 2013
Meeting in Cambridge or
Interim report meeting
September 2013 York
Interim report
March 2014
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The Ecology of Brown Rats (
Rattus norvegicus) on Rum
Meeting in Cambridge or
Interim report meeting
March 2014
York
Interim report
September 2014
Meeting in Cambridge or
Interim report meeting
September 2014 York
Draft thesis
August 2015
Final thesis (submission)
September 2015
Examination
(unknown)
Cambridge
8) Outcomes and Outputs
1. Submission of PhD thesis
2. Dissemination of findings to stakeholders
• Interim reports to SNH annually (August 2013, August 2014)
• Full scientific report to SNH by end December 2015, including all datasets
generated by the project
3. Dissemination of findings to the research community
• Published papers x 3 in peer reviewed journals (examples of target journals
include
Journal of Applied Ecology, European Journal of Wildlife Research,
Animal Conservation)
• Presentation at conferences x 2 e.g. BES, Mammal Society
4. Dissemination of findings to the Rum community and wider public
• Six monthly informal reports on progress of research and key findings
• Information display in Rum Community Centre and Rum Visitor Centre
• Articles in local and national press
• Press releases and interviews with media as appropriate (with the prior approval of
SNH/SEPA)
• Features in Anglia Ruskin University/FERA websites (with links to published papers)
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The Ecology of Brown Rats (
Rattus norvegicus) on Rum
9) Payments
Payment will be made at six-monthly intervals subject to acceptance of the specified outputs
as follows:
Payment 1
1st March 2013
£8,200
Payment 2
3rd September 2013
£8,200
Payment 3
1st March 2014
£8,200
Payment 4
2nd September 2014
£8,200
Payment 5
3rd March 2015
£8,200
Payment 6
1st September 2015
£8,200
10)
Health & Safety
As part of any client/contractor relationship, both parties have duties under H&S legislation.
Similarly, if a contractor employs sub-contractors to carry out some or all of the work
contained within the specification given for the contract, all parties have health and safety
responsibilities. The extent of the responsibilities of each party will depend on the individual
circumstances of the project.
In order to meet SNH requirements, we need to be satisfied that prospective contractors are
competent to undertake the work described and have health & safety policies and
procedures in place. These must address employee training and safety, and the risks and
hazards associated with the work.
SNH will require the following to be adopted by the University, and if and when required,
SNH will be entitled to see:
1. Evidence of Competency (e.g. qualifications, training, experience, references, CVs etc.)
for the student
2. A copy of your Health and Safety Policy Statement
3. A statement showing your ‘Safe Method of Operation’ and any generic Risk
Assessments for the type of work you intend carrying out.
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The Ecology of Brown Rats (
Rattus norvegicus) on Rum
4. A copy of your Public Liability Insurance certificate and, where appropriate, Employer’s
Liability Insurance certificates, or other evidence of insurance cover (e.g. a broker’s
letter).
5. In addition to your own statutory responsibilities under the Reporting of Injuries,
Diseases and Dangerous Occurrences Regulations (RIDDOR) 1995, SNH will require
you to report all accidents, dangerous occurrences and near-misses that occur whilst
you and the student are undertaking the studentship, to the SNH Project Officer.
6. You will be required, in liaison with the SNH Project Officer, to identify hazards
associated with the work, to complete the necessary COSHH (Control of Substances
Hazardous to Health) and final Risk Assessments and to confirm their ‘Safe Method of
Operation’ statement. This will include ensuring that any previously supplied generic risk
assessments have been tailored to the specific work to be undertaken. This must be
agreed with the SNH Project Officer before the work commences.
end
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