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Rattus norvegicus -Berkenhout and Rattus exulans Peale.
A thesis presented
in partial fulfilment of the requirements for the degree
of Master of Science in Zoology
at
Massey University Andre,,, Mark Philip Dick
1985
scr q,
3.,2~p2,oq'f3~ {"°DlC
ABSTRACT
Snap-trapping information and diet analysis were used to investigate the coexistence of Rattus norvegicus and Rattus exulans with one another and with indigenous avifauna on Kapiti Island (1,965ha, 400 51 'S., 1740 56'E.). The period of trapping was one year (May 1983 to April 1984) and a diversity of habitat types were involved. Areas were trapped for a three day period after three days of prebaiting and most areas were trapped three times during the year. Reproductive and rrorphometric p:i.rameters were also recorded for the rat populations and an alternative form of estimating density, nocturnal rat counts, was tested. Attempts were also made to measure the artoreal activity of rats using chalk dust tracking µ3.per.
The density estimate for the combined populations (15.06 rats/100 trap-nights) is high when canp:i.red with mainland rat populations. Density varied with habitat &1d season, the highest density index being obtained in lowland grass, the lowest along a stony beach. A Standard Minimum estimate of 63 rats/ha was derived for the lowland grass area. Changes in density with season varied from area to area although there was a p:i.rticular tendency for variations in spring. Species canposition was different between habitats. Of eight areas trapped .!3.:._ norvegicus was the predominant species in five. R. exulans was the predominant species in three areas and occurred in six. Seasonal fluctuations in species ratios were observed and in the three R.
exulans areas a high negative correlation existed between the abundance of each species. Male R. exulans were heavier (x=85.92g) than females (x=78.98g) although the reverse situation
occurred in R. norvegicus, (male x=209. 76g, female x=222. 07g).
Reproduction in both species was seasonal with breeding activity peaking in surnner and spring. Length of breeding season, average frequency of litter production and mean foetus number were greater in R. norvegicus.
structure.
R.exulans showed greater fluctuations in age
Of the three main food categories measured, invertebrates, vegetation and seeds, the invertebrate fraction was, in terms of mean percentage volume and frequency of occurrence, the most important for both species. R. exulans had a less varied diet and was more reliant on invertebrates. Lepidopteran larvae were the most frequently eaten invertebrates with Araneida, Coleoptera, Orthoptera, Dipteran larvae and Chilopoda also occurring.
Invertebrates formed a greater part of the diet in sum.~er months.
Diet strongly reflected the habitat in which rats were trapped.
Distinctly different diets were noted in animals inhabiting forest when compared with those fran grassland. The proportion of exotic vegetation and seed was rrore pronounced in the grassland habitats . Although the overlap in diet was considerable, particularly with
.
the invertebrate types eaten (52 types identified, 17 eaten _by only one species) the differences in volumes eaten were substantial. Birds did not feature heavily in rat diet and no instances were recorded of kiore having eaten bird remains.
Nocturnal rat oounts appear an unreliable alternative to trapping as a density measure and kiore do not appear to forage arboreally.
The changes in species ratio, density and diet with area are discussed in terms of canpetition theory. It is hypothesised that
iii
R. norvegicus is cornpetitively superior and excludes R. exulans from mutually desirable habitats. The mechanisms of the competition are unclear although available evidence suggests that competition for food rather than competition for space is the rrore likely.
ACKNOWLEDGEMENTS
Many people have assisted in compiling this project. My supervisor, Dr. John Skipworth, was always on hand when needed and his contribution is greatly appreciated.
While on Kapiti the Daniel family were hospitable and encouraging and I am indebted to then. Trevor Hook, Geoff Alexander, Bob Cairns, Tony Beauchamp and Ti..ct I..ovegrove provided enjoyable company and offered ideas,
Beauchamp kindly assisted in identifying
advice and invertebrate
rats. Tony fragments.
Dr. Henrik Moller (Ecology Division, D.S.I.R., I..ower Hutt) willingly contributed information and advice on rodent ecology as did Dr. Ian Atkinson (Botany Division, D.S.I.R., I..ower Hutt), Dr.Phil M<x:)rs (Wildlife Service, Wellington), Duncan Cunningham (Wildlife Service, Wellington), Ian McFadden (Wildlife Service, Auckland) and Dr. Kamierez Wodzicki (Zoology Department, Victoria University).
Keith Young (Ministry of Agriculture and Fisheries, Palmerston North) and Margaret Bulfin (Botany Division, D.S. I.R., Christchurch) identified seed remains and I appreciate their effort. Jan McKenzie (Canterrury University), Prof. R. Pilgrim (Canterbury University) and Riccardo Palna (Daninion Museum, Wellington) kindly
(Entanology Division, insects.
identified the parasites. Peter McGregor D.S.I.R., Palmerston North) helped identify
V
Dr. Tom Hassard and Greg Arnold (Statistics Department, Massey University) freely provided assistance with the multivariate statistics used.
My roan-mates John Mitchell and Alan Nixon often offered advice rrost
appreciated.
of which was pertinent and all of which was Gavin Williamson ( Zoology Department, M3.ssey University) shared his cuticle analysis techniques with me.
The Iands and Survey Department provided financial assistance over the surnner spent on Kapiti and this plus their initial permission for the study is appreciated.
Colin Cook (Real Estate Agent, Palmerston North) kindly provided the use of a word processor while Sheryl Hollow (Public Relations Organisation, Palmerston North) was helpful with final photocopying. Peter McGurk (Palmerston North) assisted with final proof reading.
My parents, Natalie and Ian Dick (Napier) were a constant source of encouragement. My fiance, Sandy Bacon, patiently typed the thesis, was a ready source of comfort, diligently travelled to Paraparaumu Beach to pick me up after my Kapiti sojourns and applied the pressure needed to finish the thesis.
TABLE OF O)NTENTS
TITLE PAGE
ABSTRACT
ACKNOOLEIX;EMEN'IS LIST OF FIGURES LIST OF TABLES LIST OF PLATES
CHAPTER 1.
1 • 1 1 • 2 1 • 2. 1 1 • 2. 2 1 . 3 1 • 4 1 • 4. 1 1 • 4. 2 1 . 4. 3 1 • 4. 4 1 . 4. 5 1 . 4. 6 CHAPTER 2.
CHAPI'ER 3.
3. 1 3.2 3.3 3.4 3.5 3.6 3.7
CHAPTER 4.
4. 1 4. 1 • 1 4. 1 • 2 4. 1 • 3 4. 1 • 4
4.2 4.3 4. 3. 1 4.3.2 4.3.3 4.3.4 4.4 4. 4 .1 4.4.2 4.4.3
INTRODUCTION PREAMBLE
DESCRIPTION OF RATS Norway rats
Kiore
RATS
rn
KAPITI ISLAND KAPITI ISLANDGeneral description Climate
Geology Vegetation Fauna
Cultural influences
AIMS
METHODS
TRAPPING
DESCRIPTION OF S'IUDY AREAS
FIELD EXAMlliATIONS, MORPHOMETRICS AND REPROOOCTION
LABORATCRY EXAMlliATIONS, REPROCUCTION AND DIET
ARBOREALITY
NCCIURNAL RAT CDUNTS
STATISTICS RESULTS
TRAPPING
Density indexes Species ratio
Correlation between density and s-pecies ratio
Density and s-pecies ratio of areas trapped once
MJRPHOOEI'RICS REPROCUCTION Sex ratio
Age (weight) classes Reproductive activity Maturity
DIE1'
Invertebrates Foliate vegetation Seed and fruit
Page i ii
V 1.X
X
xii 1 1 3 3 6 7 8 8 9 9 11 13
14 16 17 17 19 27 28
31 32 32 34 34 34 34
39 39 42 47 47 47
• 52 54 54 54 57 63
4.4.4 4.4.5 4.4.6 4.4.7 4.5 4.6 4.7 4.8 4. 8. 1 4.8.2 4.8.3 4.8.4 4.8.5
Other categories
Diet analysis, species differences Diet analysis, area differences Diet analysis, seasonal differences PARASITES
AROORFALITY
NOCI'URNAL RAT muNTS MISCELLANEDUS RESULTS F.dge Effect
Prebaiting
Post breeding season females Weight of non pregnant females Norway rat sex ratio on Line 3
64 64 64 69 70 70 71 71 71 71 74 74 74
O!API'ER 5. DISOJSSICN 75
5.1 ME:I'HODS USED 5.1.1 Trapping 5.1.2 Reproduction 5.1 .3 Diet
5.2 DENSITY AND SPECIES RATIO
5 • 3 K>RPHOMEI'RICS
5.4 REPROOOCTIOO 5. 4. 1 Norway rats 5.4.2 Kiore
5.5 DIET
5.5.1 Introduction 5.5.2 Kiore
5.5.3 Norway rats
5. 5. 4 · Lepidoptera larvae and prairie grass 5.5.5 Surrmary
5.6 AROOREALITY AND NOCTURNAL RAT CDUNTS 5.7 ffiEXISTENCE AND CLMPEI'ITIOO
75 75 77 79 80 84 85 85 88 89 89 89 92
seed 94
95 96 97
REFERENCES 102
Apperrlix 1 Vegetation types of Kapiti Island. 120 Appendix 2 Location of possum trap lines mentioned in
the text. 121
Appendix 3 Raw trapping results. 122
Apperrlix 4 Density indexes with confidence limits. 123 Appendix 5 Seasonal density indexes with confidence
limits. 124
Apperrlix 6 Two-way PNCVA of kiore weight with sex and
area. 125
Apperrlix 7 Monthly female sexual condition. 126 Appendix 8 Relative frequency of occurrence for nine
food classes. 127
Apperrlix 9 MAOOVA arrl D.F .A. tarameters. 128 Appendix 10 Seasonal% volume results for the
invertebrate, vegetation and seed fractions. 131
Figure
1 •
2.
LIST OF FIGURES
LOCATICN OF KAPITI ISLAND AND AREAS TRAPPED r::uRING THE STUDY.
TOI'AL DENSITY INDEXES FOR AREAS TRAPPED MClIB THAN CNCE.
3 . SEASCNAL CHANGES IN DENSI'IY INDEX AND SPECIES RATIO.
4.
5.
6.
7.
8.
9.
3A. Line 1 3B. Line 2 3C. Line 3 3D. Line 4 3E. Line 5 3F. Line 7 3G. Grid 1
STANDARD REMOVAL DENSI'IY ESTIMATE FOR GRID 1.
TOTAL SPECIES RATIO FOR AREAS TRAPPED MORE THAN CNCE.
CHANGES IN WEIGHT CLASS FR.B:2UENCY WITH SEASCN.
6A. Kiore . 6B. Norway rats
CHANGES IN WEIGHT CLASS FRml]ENCY WITH AREA.
7A. Kiore
7B. Norway rats
SEASCNAL CHANGES IN REPRODUCTIVE PA...-qAMETERS.
SA. Norway rats SB. Kiore
FREX:2UENCY OF OCOJRRENCE OF NINE MAJOR FCX)D ITEMS FOR POTH RAT SPECIES.
1 0. FREX:2UENCY OF OCOJRRENCE OF NINE MAJOR FCX)D ITEMS IN:
1 OA. Line 1 10B. Line 2
1
oc.
Line 31 OD. Line 4
10E. Line 5 1 OF. Line 6 1 OG. Line 7 1 OH. Grid .1
Page
10
35
36 36 36 36 37 37 37 38 40
50
51
53
58
65 65 65 65 66 66 66 66
11.
12.
13.
DIFFERENCES IN THE VOLUMES OF INVERTEBRATE, SEED AND VEGETATION EATEN DISPLAYED AS DISCRIMINANT FUNCTION AXES FOR:
11A. Kiore trapped seasonally in Grid 1 11 B. Kiore trapped seasonally in Line 4 11 C. Kiore trapped seasonally in Line 3
11 D. Norway rats trapped seasonally in Grid 1 11 E. Norway rats trapped seasonally in Line 2 11 F. Norway rats trapped seasonally in Line 1 11G. Norway rats and kiore
DIFFERENCES IN THE VOLUMES OF INVERTEBRATE, SEED AND VEGETATION EATEN DISPLAYED AS DISCRIMINANT FUNCTION AXES FOR:
12A. Norway rats in Norway rat areas 12B. Kiore in kiore areas
LCCATION OF RATS SIGHTED IXJRING NCCIURNAL CDUNTS AROOND THE RANGATIRA TRAO< SYSTEM.
67
68
73
Table 1.
2.
3.
4.
LIST OF TABLES
TRAP EFFORT AND r.mTHS TRAPPED FOR EAGI ARFA. SIGNIFICANCE OF SEASCNAL CHANGE IN SPECIES RATIO.
Cl)RRELATION Cl)EFFICIENTS BETWEEN SPECIES RATIO AND DENSITY INDEX FOR SEASONAL CHANGES.
'TOI'AL WEIGHT RESULTS.
5. ARFA WEIGHT DIFFERENCES TESTED BY t TEST AND PNJVA.
6.
7. 8. 9. 10.
11 .
12A.
12B.
12C.
13. 14.
15.
5A. Norway rats 5B. Kiore -
SEASCNAL WEIGHT OfANGFS. SEX RATIOS.
SIGNIFICANCE OF CHANGES IN WEIGHT (AGE) CLASS.
RATIO OF OLD TO YOUNG RATS.
DIET PERCENTAGE CCQJRRENCE RESULTS FOR SPECIES AND ARFA.
DIET PERCENTAGE VOLUME RESULTS FOR SPECIES AND ARFA.
FREX:_UENCY OF CCOJRRENCE OF INVERTEBRATE FCX)[) ITEMS.
FREX:_UENCY OF CCOJRRENCE OF SEED FCX)O ITEMS.
~ C Y OF OCCURRENCE OF PLANT FOOD ITEMS. NCCIURNAL RAT Cl)UNTS.
ffiv1PARIS0N BEIWEEN HYPOTHETICAL DENSITY
INDEXES.
DESOUPTION OF PREFERRED HABITI\TS.
Page 18 41
41
43
44 45 46 48
49 49 55
56
59
61
62 72
77
83
Plate Page
1 • KIORE. 4
2. NORWAY RAT. 4
3. LINE 1. 20
4. LINE 2. 20
5. LINE 3. 22
6. LINE 4. 22
7. LINE 5. 24
8. LINE 6. 24
9. LINE 7. 26
10. GRID 1. 26
