Observations on the prevalence of nest-buildingin non-breedingTO strain mice and their use oftwo nesting materials

C. M. SherwinDivision of Animal Health and Husbandry, Department of Clinical Veterinary Science, University ofBristol, Langford House, Langford, Bristol BS187DU, UK

Summary

The spontaneous performance of nest-building behaviour by non-breeding laboratory micesuggests that routinely providing nesting material might be a suitable environmentalenrichment. If nesting material is to be provided routinely, this should have characteristicswhich are preferred, or at least accepted by a considerable proportion of the animalpopulation; it should also be inexpensive. The present study therefore examined theprevalence of nest-building behaviour in 39 individually-housed, non-breeding, female mice,and their preferences for a commercial nesting product and a less expensive source of material(paper towels). Within minutes of the materials being placed in the cages, the mice beganmanipulating the paper towels. Thirty-six of the mice subsequently constructed nests duringthe first dark phase after the materials had been placed in the cage - the remaining three miceconstructed nests during the following 48 h. The nests were usually constructed from amixture of the two materials, though observations indicated the mice might have preferredcharacteristics of the inexpensive paper towels. There was a strong tendency to build nests inthe same location used for sleeping prior to the nesting material being provided, and similarly,the mice were conservative in the site chosen to build a second nest after the first wasremoved. The most frequently chosen site for nest-building was under the feeder. Otherstudies have reported a high motivation for nest-building behaviour, widespread performanceamongst many strains, and nest-building as a thermoregulatory behaviour by animals housedin standard laboratory air temperature. In conjunction with these findings, the present resultssuggest that routinely providing paper towels is an inexpensive and practical means ofenvironmental enrichment for non-breeding, laboratory mice.

Keywords Environmental enrichment; mice; nesting behaviour; preferences; welfare

It has been argued that to ensure goodwelfare, the husbandry of captive animalsshould allow them freedom to perform most'normal' behaviours (e.g. FAWC 1993), orenable them to perform most behaviourswhich their progenitors/wild conspecificsexhibit (e.g. Veasey et al. 1996). Using thislatter approach, Dawkins (1989) reported thatRed Junglefowl, the ancestors of modernstrains of laying hen, spent 34% of the dayscratching and pecking at ground litter whilst

Accepted 10 June 1996

searching for feed. The cage environment ofmodern layer hens prevents them fromperforming these behaviours and the occur-rence of abnormal, sometimes fatal injuriousbehaviours have been linked with this short-coming. It has been reported that wild micefrequently build nests (Van Oortmerssen1971, Estep et al. 1975, Castle & Marshall1990, Brain 1992) and when materials areprovided, inbred strains of laboratory micebuild nests of a comparable or slightly larger

Laboratory Animals (1997) 31,125-132

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size than those built by wild-type counter-parts (Estep et al. 1975, Lynch 1977). But,although both breeding ILisk et al. 1969, Lisk1971, Wainwright 1981, Broida & Svare 1983,Schneider & Lynch 1984, Scharmann 1991,Brain 1992) and non-breeding (e.g. Lisk et al.1969, Lisk 1971, Van Oortmerssen 1971,Roper 1973, Scharmann 1991, Brain 1992)laboratory mice build nests when materialsare available, nesting materials are usuallyprovided routinely only for breeding females.Therefore, non-breeding mice are commonlyhoused under conditions which preclude a'natural' behaviour that is frequently per-formed by wild-type progenitors. It is possi-ble that such husbandry is sub-optimal withregards to ensuring good weUare.

Nest-building by laboratory mice can becategorized as either maternal or non-mater-nal. The former has been widely investigatedand the effects of environmental (Noirot1974, Lynch & Possidente 1978, Porter &Busch 1978), genetic (Lynch 1977, Lynch &Possidente 1978, Nee et al. 1992) andendocrinological (Voci & Carlson 1973,Lynch & Possidente 1978, Lisk et al. 1969,Lisk 1971) factors have been described indetaiL Although there are many reports ofnon-maternal nest-building by mice (e.g. Lee& Wong 1970, Van Oortmerssen 1971, Lee1973, Roper 1973, Schneider et al. 1973, Voci& Carlson 1973, Noirot 1974, Glaser &Lustick 1975, Lynch 1977, 1980, Lynch et al.1986) its occurrence under laboratory condi-tions has less frequently been the focus ofinvestigation. If it is ascertained that provid-ing nesting materials is advantageous e.g. bypromoting natural behaviours, increasingbehavioural diversity, or decreasing foodintake with no effect on growth (Lacy et al.1978, Stephenson &Malik 1984), it could beargued that we should routinely supply thesematerials to both breeding and non-breedinganimals. But, if provision of such environ-mental enrichment is to be widely adopted,the desired changes to behaviour or perfor-mance of the appropriate activity should beexpressed by a large proportion of thepopulation. One aim of this investigationwas to examine how prevalent spontaneousnest-building behaviour is amongst non-breeding mice.

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When suggesting changes to animal hus-bandry, it is important to recognize practicalconstraints. If nesting material is to beroutinely supplied to non-breeding animals,it should be readily available, easily handledby technicians and inexpensive. Althoughcommercial nesting materials for pet rodentsare available, these are almost certainlyprohibitively expensive and can be trouble-some to handle. Encouragingly, laboratorymice (Roper 1973 1975abc, Rajendram et al.1987, Blom et al. 1993, van de Weerd et al.1994), rats (Bradshaw & Poling 1991) andhamsters (Jansen et al. 1969) will build nestsfrom inexpensive paper strips or papertowels. Therefore, the second aim of thepresent study was to determine whethermice exhibited a preference for an inexpen-sive source of paper or a more expensive,fibrous material for the construction of nests.

Materials and methods

Thirty-nine virgin, female TO mice bred 10months previously in the laboratory werehoused individually in standard mouse cagesmeasuring 33 x 20 x 19cm (WxD x H) andcontaining 1cm of sawdust. The mice hadbeen reared in single-sex, sibling groups priorto being placed in the experimental cages andhad no prior experience of potential nestingmaterials other than sawdust.

For seven days after the mice were placedin the cages, scans were made (as describedbelow) to determine the site preferred by themice for sleeping. After the 16:00 h scan onthe seventh day, two plastic pots 9 cm highand 10cm diameter were placed at the rear ofeach cage. A wad of 100% cellulosic fibrebedding ('Nestle Down', Interpet, Surrey, UK)weighing approximately 4.5 g was placed inthe left pot for 20 mice and in the right potfor the remainder. In the other pot was placeda sheet (34 x 20 cm) of 2-ply paper hand-towel('Hywipes', Bristol Industrial Protections,Bristol, UK) weighing 3.2 g. The pots wereretained in a vertical position against the rearwall by metal clips and a small amount ofboth materials was left remaining visibleabove the rim of the pot. Scans werecontinued for the following six days. All

Nest-building in non-breeding mice

fibrous and paper nesting material was thenremoved and replenished with fresh material,placed in the pot opposite to that in which ithad been supplied previously.

Table 1 The locations preferred by mice forsleeping, prior to nesting materials being placedin the cage

No. micechoosing site

Sleeping "10 of as mostlocation No. scans scans* preferred t

Under feeder 152 34.8 16Under drinker 118 27.0 10Rear of cage 72 16.5 6Other 95 21.7 7'Active' 191

TOTAL 628 39

*Including only those scanswhen a mouse was recorded assleepingtBased on the modal frequency recorded for each mouse

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Observations were made in the followingway. On two or three occasions each day (at10:00,13:00 or 16:00h) the experimental roomwas entered quietly and each cage scanned. Ifthe mouse was sleeping or was in a nest andhad obviously just awoken after being dis-turbed by the observer, the position of themouse was noted. If the mouse was in a nest,the materials used in its construction werealso noted. During the period prior to nestingmaterial being placed in the cage, the sleepingsites were designated as 'under the feeder','under the drinker', 'in the rear third of thecage' or 'other' (i.e. the remainder of the cage).When the pots and nesting materials werepresent, the location 'rear of the cage' wasreplaced by 'the pot supplying paper' and 'thepot supplying fibre'. The mouse was recordedas 'active' if it was moving about the cage.

The room lights (100W incandescentbulbs) were on between 08:00-17:00h andthe ambient temperature was maintained at21°C with a range of ± 1°C.

Table 2 The locations preferred by mice for nest-building, and the materials used in construction of thenest

Materials used No. mice choosing sitelNest location in nest No. Scans %of scans* material as most preferredt

Under feeder Mix 368 37.4 15.5Paper 39 3.9 2.0Fibre a 0.0None 3 0.3

Under drinker Mix 114 11.6 3.0Paper 25 2.5Fibre 0 0.0None 15 1.5

Pot with paper Mix 97 9.9 4.5Paper 34 3.5 2.0Fibre 0 0.0None 0 0.0

Pot with fibre Mix 89 9.1 5.5Paper 0 0.0Fibre 8 0.8None 1 0.1

Other (main cage) Mix 186 18.9 7.5Paper 2 0.2Fibre a 0.0

None 2 0.2'Active' 322

TOTAL 1305 39

*Including only those scans when a mouse was recorded as sleepingtBased on the modal frequency recorded for each mouse. When the mouse was equivocal (n=4 mice) its score was sharedbetween the two options it chose most frequently

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Results

Prior to the nesting materials being placed inthe cages, the majority of mice preferred tosleep under the feeder (Table l) thoughseveral consistently slept in the rear or mainsections of the cage which did not provideoverhead cover. None of the mice con-structed nests with sawdust as describedpreviously (Sherwin 1996a).

Within 2-3 min of the nesting materialsbeing placed in the cages, many mice hadpulled the paper towel from the pot into themain cage, investigated, chewed and ma-nipulated the sheet. Although not recordedsystematically, this gave a strong impressionthat the paper was immediately more attrac-tive than the fibre.

The cages were scanned a total of 1305times when the nesting materials werepresent. The mice were recorded as activeduring 24.7% of these. Table 2 shows that themost frequently constructed nest was builtunder the feeder and comprised a mixture ofboth the fibre and paper. Sawdust was usuallypresent in the nests, though this appeared tobe due to the trapping nature of the fibrousmaterial rather than having been deliberatelyincorporated by the mice. The second mostfrequently built nest, also a mixture of thematerials, was situated in the main area ofthe cage i.e. with no overhead cover otherthan that provided by the nest.

All 39 mice used one or both of thematerials to construct a nest. Two miceconstructed their nest entirely of paper whileall the remainder constructed their nest froma mixture of the paper and the fibre. The nestswere built rapidly; 36 mice built a nest duringthe first dark phase after the materials wereinitially placed in the cages and 37 mice builtnests during the first dark phase after freshmaterials were provided. The longest periodthat elapsed before a nest was built was 72 h.

There was a strong tendency to constructthe first nest in the same location as the sitechosen for sleeping prior to the materialsbeing placed in the cageSj 25 nests were builtin the same location, 4 changed to a locationin one of the pots, 4 changed to a differentlocation for no obvious reason, and 6 micehad previously slept at the rear of the cage

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thus necessitating a change in location.because the pots occupied this position.

The mice were also conservative in theirchoice of nest location after fresh nestingmaterials were supplied. Twenty-one builttheir second nest in the same location afterthe first nest was removed. Of the 18 micewhich were recorded as changing site, thisincluded 10 which changed to building theirpests in one of the pots. In addition, it shouldbe noted that a change in site between'feeder' and 'drinker' (and to a lesser extent'other' areas of the cagel might in reality haverequired a change in location of only a fewcentimetres.

The nests built by the mice varied in sizeand complexity. Two individuals constructedsimple mats and slept on top of thesewhereas all the other nests provided overheadshelter with varying densities of cover. Somenests were constructed with an entrance/exittunnel and an enclosed, central sleepingchamber: others were a simple aggregationwhich the mouse sheltered under. Most ofthe nests appeared to be a homogenousaccumulation of the fibrous material andshredded pieces of the paper, though 3-4nests were more highly organized in that thepaper was apparently used to line the insideof the nest while the fibre formed the majorexternal structure. The mice generally usedall the materials available, however, three ofthe mice left some of the fibrous materialunused in the pot for several days.

DiscussionThe principal· finding of this study is thatwhen 39 non-breeding mice were providedwith nesting materials, each individualrapidly and spontaneously performedcomplex nest-building behaviours andconstructed a nest. This was despite the micehaving no prior experience of these materialsor the opportunity to build nests other thanheaping sawdust provided as floor substrate(see Sherwin 1996a). This indicates thathousing non-breeding mice without nestingmaterials precludes them from performing abehaviour which is either innate or quicklylearnt by a great proportion of laboratory mice(strain and sex differences notwithstanding).

Nest-building in non-breeding mice

The present study was conducted usingindividually housed female mice, a form ofhousing rarely practised in laboratories.Extrapolation of these findings to grouphoused animals therefore needs to be exam-ined, though previous reports (Koller 1956,Lynch &. Possidente 1978) and unpublishedobservations during pilot trials for this studyindicate that group housed females alsospontaneously build non-maternal nests.

The findings of this study support otherwork which indicates the welfare of labora-tory mice may be improved if we providethem with nest-building material. Firstly, ithas been argued (e.g. Dawkins 1990, Sherwin&. Nicol 1996) that animals are more likely toexperience suffering if we do not providethem with resources for which they arehighly motivated. It has been shown thatmice will repeatedly build nests which areremoved daily (Lee &. Wong 1970, Lee 1973,Roper 1975a, Lynch 1977, Batchelder et a1.1982), they will work by lever-pressing togain access to nesting material (Roper 1973,1975abc, see also Jansen et a1. 1969, Oley &.Slotnick 1970) and will traverse aversiveobstacles to gain access to deep sawdust(Sherwin &. Nicol 1995, Sherwin 1996b).These observations indicate that mice arehighly motivated to gain access to nestingmaterial and/or perform nest-building beha-viour. Although the motivation for gatheringnesting material appears to be less strongthan that for food, mice nonetheless willcompensate for an increased work require-ment to maintain their nest-building beha-viour (Roper 1975b). Secondly, the functionof non-maternal nests may be directly relatedto welfare which is negated in the absence ofsuitable nesting materials. It is widelyassumed that nest-building is thermo-regulatory and this is supported by evidencethat nest-building is more prevalent or moreefficient at lower air temperatures (Lee &.Wong 1970, Lynch 1973, Glaser &. Lustick1975, Lynch et a1. 1976, Lynch &. Possidente1978, Batchelder et a1. 1982, Rajendram et a1.1987), or is related to other thermoregulatorycharacteristics (Stephenson & Malik 1984,Lynch et a1. 19861.But, it is illuminating tonote an overwhelming number of studieshave reported that non-maternal nest-build-

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ing occurs at 21-26°C i.e. standard laboratorytemperature or higher (Lee &.Wong 1970, VanOortmerssen 1971, Lynch 1973, 1977, Roper1973, 1975abc, Voci &. Carlson 1973, Estep eta1. 1975, Glaser &. Lustick 1975, Mulder 1975,Lynch &. Possidente 1978, Lynch 1980,Batchelder et a1. 1982, Lavery &. Hay 1984,Stephenson &. Malik 1984, Lynch et a1. 1986,Rajendram et a1. 1987, Blom 1993, van deWeerd 1994). The occurrence of nest-buildingat such air temperatures is perhaps notsurprising considering the thermoneutraltemperature of mice is 27-36°C (Glaser &.Lustick 1975, Lynch et a1. 1976, Stephenson&. Malik 19841,but, this suggests that if weplace mice in standard laboratory conditionsof 21°C without providing nesting material,this precludes them from manipulating theirmicro-environment to preferred conditions.Thirdly, allowing mice to build nests mighthave non-thermal consequences which bene-fit welfare. For example, building a nest mightallow the animal to remove itself from directlight and thus facilitate a reduction in retinaldegeneration (Clough 19821,regulate auditorystimulation (Blom 19931,facilitate antipredi-tor behaviour or camouflage (Rajendram et a1.198n increase behavioural diversity or reduceextraneous stimulation.

These findings also support previous evi-dence that providing a pre-formed nest-box asa form of environmental enrichment may beinappropriate. Although some mice buildnests in the pots and the impression wasgained that these mice were less easy todisturb, the number of animals using the potswas relatively small. Previous reports haveshown that mice are not highly motivated touse empty pots for sleeping in (Sherwin1996b, Sherwin &. Nicol 19961and do not usetubular shelters unless loose floor substrate(sawdust) is removed (Sherwin 1996al. Inconjunction with the present results andthose of Roper (1975abc), it seems thatmanipulable material is preferred to a rigid,pre-formed shelter/nesting area.

The mice showed no clear preference forconstructing nests of either the paper or thecellulosic fibrous material. However, selec-tive use of the paper for lining some nests andthe rapidity which this material was initiallymanipulated by the mice suggests the paper

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might have had more attractive qualities.Mice can be highly discriminating in theirchoice of materials for nests. Roper (1975c)reported that mice differed in the amount ofwork they would perform for different widthsof paper strip, and Blom (1993) reported thatthe preference of mice for shredded filterpaper as bedding material was so great that itmasked preferences between wood-chips.Mulder (1975) reported that pregnant femalemice preferred bedding materia.ls which werewood in origin. But, it appears that in general,if mice are offered a variety of materials fornest-building they will use a mixture (VanOortmerssen 1971, Mulder 1975, presentresults). This might be due to investigatorsproviding insufficient quantity of a singlematerial, or possibly an attempt by the miceto camouflage the nest. Whichever, theprobability remains that mice prefer toconstruct nests from a variety of materials.

The mice showed considerable individualdifferences in the shape and complexity ofthe nests they built, although individualsappeared to be consistent. Differences in theshape of non-maternal nests and the amountof material used have been described else-where (Voci & Carlson 1973, Lisk et al. 1969,Lavery & Hay 1984, Nee 1992) and it hasbeen reported that significant strain and/orsex differences occur in the form of the nestor the amount of material used (Lee &Wong1970, Lee 1973, Estep et al. 1975, Lynch1977, Batchelder et 01. 1982). The functionalsignificance of these differences and theirconsequences on welfare have not beendetermined, although the shape and com-plexity of nests may be related to ambienttemperature [Lee & Wong 1970, Glaser &Lustick 1975, Rajendram et al. 1987).

If nesting material is to be provided as aroutine form of environmental enrichment,expense and practicality would beconstraints. Based on retail prices, each papernest cost approximately £0.005 and each fibrenest approximately £0.18. Since the mice hadno clear preference for either of the materials,it seems appropriate to suggest that papertowels are a low-cost option for providingnesting-materials which may satisfy thepredilection of mice for nest-building, thoughthe possibility ~hat a selection of materials

Sherwin

may be preferred deserves further attentionand the composition and properties of thepaper may need to be determined for someexperimental protocols (e.g. see Potgieter &Wilke 1996). In the present study the papertowels were supplied by placing them in potsbut it has been reported that if nestingmaterial is placed in the feed hopper or on theroof of the cage, mice will tug this throughthe bars and subsequently use it for nest-building (Lee & Wong 1970, Lee 1973, Lynch1973, 1977, 1980, Estep et al. 1975, Lynch &Possidente 1978, Lynch et al. 1976, Nee et al.1992); this is clearly a more practicablemethod of providing nesting materials.

The present study examined the behaviourof only one strain of mice. Previous reportsindicate that a wide variety of strainsconstruct non-maternal nests when given theopportunity, namely, CPBs, c57Black/LiA,DBA/LiA, CBA/BrA (Van Oortmerssen 1971),C57Bl/6j, Swiss-Webster (Schneider et al.1973, Rajendram et al. 1987), DBA/2j [Lee &Wong 1970, Schneider et al. 1973), RAP(Roper 1973, 1975abc), ARS Ha (ICR) Swissmice (Mulder 1975), A/J, BALB/cJ, CBA/J,C3H/HeJ, C57BL/6J (Lee & Wong 1970, Estepet al. 1975, Lynch 1977, Batchelder et al.1982), DBA/1J [Lynch 1977) C57BL/6Jlco,HSjlbg (Lynch & Possidente 1978, Lynch1980, Batchelder et al. 1982), BALB/clbg,C3H2lbg (Batchelder et al. 1982), BALB/cBnco (Blom 1993), C57BL/6JlcoU andBALBjcAnCryCpbRivU Ivan de Weerd1994). I have found only three reports ofmice not building nests; Lavery & Hay(1984) reported that on 3 of 220 scans, anest was not built by C3H/HeGIF/Wehior C3H/He inbred strains; Glaser & Lu-stick (1975) reported that nests were notbuilt at ambient temperatures greater than25°C; and Estep et al. (1975) reported thatwild mice were significantly more likelynot to build a nest than inbred strains. Inconjunction with the present report, thisindicates that when given the opportu'nity, nest-building is performed by a greatproportion of non-breeding laboratorymice. Given the ease and inexpense ofproviding suitable nesting materials, thelack of evidence for detrimental effectsand the prevalence and strength of

Nest-building in non-breeding mice

motivation to perform nest-building, itwould seem that routinely providing papertowels as nesting material is an effectiveand inexpensive form of appropriate en-vironmental enrichment for laboratorymice.

Acknowledgments I thank Dr C J Nicol forconstructive criticism at all stages of this study andDr C Lindberg for comments on an earlier version ofthis manuscript. The work was funded by the HomeOffice, UK.

References

Batchelder P, Lynch CB, Schneider JE (1982) Theeffects of age and experiences on strain differencesfor nesting behaviour in Mus musculus. BehaviorGenetics 12, 149-59

Blom HJM, Baumans V, Van Vorstenbosch qAHV,Van Zutphen LFM, Beynen AC 119931Preferencetests with rodents to assess housing conditions.Animal Welfare 2, 81-7

Blom HJM (1993) Evaluation of housing conditionsfor laboratory mice and rats. PhD thesis, Uni-versity of Utrecht, The Netherlands

Bradshaw AL, Poling A (1991) Choice by rats forenriched versus standard home cages: plastic pipes,wood platforms, wood chips, and paper towels asenrichment items. TournaI of the ExperimentalAnalysis of Behaviour 55, 245-50

Brain PF (19921Understanding the behaviours of feralspecies may facilitate design of optimal livingconditions for common laboratory rodents. AnimalTechnology 43,99-105

Broida J. SVare B (1983) Mice: progesterone and theregulation of strain differences in pregnancy-induced nest building. Behavioral Neuroscience 97,994-1004

Castle JP, Marshall PE (1990) The captive manage-ment of a breeding colony of Ryuku mice (Muscaroli). Animal Technology 41, 191-6

Clough G (1982) Environmental effects of research onanimals used in biomedical research. Biology Re-views 57, 487-523

Dawkins MS (1989) Time budgets in Red Junglefowlas a baseline for the assessment of welfare indomestic fowl. Applied Animal Behaviour Science24, 77-80

Dawkins MS (1990) From an animal's point of view:motivation, fitness, and welfare. Behavioural andBrain Sciences 13, 1-61

Estep DQ, Lanier DL, Dewsbury DA (19751 Copula-tory behaviour and nest-building behaviour of wildhouse mice IMus musculusl. Animal Learning &Behaviour 3, 329-36

Farm Animal Welfare Council (1993) Second reporton priorities for research and development in farmanimal welfare. Tolworth: MAFF

131

Glaser H, Lustick S (1975) Energetics and nestingbehaviour of the northern white-footed mouse,Peromyscus Leucopus noveboracensis. Physiologi-cal Zoology 48, 105-13

Jansen PE, Goodman ED, Jowaisas 0, Bunnell BN(1969) Paper as a positive reinforcer for acquisitionof a barpress response by the golden hamster.Psychonomic Science 16, 113-14

Koller G 119561Hormonale und psychische Steurungbeim Nestbau weisser Mause. Zool. Anzeig. Suppl.19, 123-32

Lacy RC, Lynch CB, Lynch GR (1978) Developmentaland adult acclimation effects of ambient tempera-ture on temperature regulation of mice selected forhigh and low levels of nest-building. TournaI ofComparative Physiology 123, 185-92

Lavery KJ. Hay DA (19841 Electrophoretic, skeletaland behavioural divergence of two C3H substrainsof mice. Journal of Heredity 75, 171-4

Lee CT (1973) Genetic analyses of nest-buildingbehavior in laboratory mice (Mus musculus IBehavior Genetics 3, 247-56

Lee CT, Wong PTP 119701Temperature effect andstrain differences in the nest-building behaviour ofinbred mice. Psychonomic Science 20, 9-10

Lisk RD, Pretlow RA, Friedmand SJ (19691 Hormonalstimulation necessary for elicitation of maternalnest building in the mouse (Mus musculus) AnimalBehaviour 17, 730-7

Lisk RD (1971) Oestrogen and progesterone synergismand elicitation of maternal nest-building in themouse (Mus musculus) Animal Behaviour 19,606-10

Lynch CB (1973) Environmental modification of nest-building in the white-footed mouse, Peromyscusleu copus. Animal Behaviour 22, 405-9

Lynch CB (1977) Inbreeding effects upon animalsderived from a wild population of Mus musculus.Evolution 31, 526-35

Lynch CB (1980) Response to divergent selection fornesting behaviour in Mus musculus. Genetics 96,757-65

Lynch CB, Possidente BP, Jr (1978) Relationships ofmaternal nesting to thermoregulatory nesting inhouse mice (Mus Musculus) at warm and coldtemperatures. Animal Behaviour 26, 1136-43

Lynch CB, Roberts RC (1984) Aspects of temperatureregulation in mice selected for large and small size.Genetical Research 43, 299-306

Lynch GR, Lynch CB, Dube M, Allen C (1976) Earlycold exposure: effects on behavioral and physio-logical thermoregulation in the house mouse Musmusculus. Physiological Zoology 49, 191-9

Lynch CB, Roberts RC, Hill WG (1986) Heterosisamong lines of mice selected for body weight. 3.Thennoregulation. Genetical Research 48, 95-100

Mulder JB (1975) Bedding preferences of pregnantlaboratory reared mice. Behaviour Research andInstrumentation 7, 21-2

132

Nee M, Rajendram EA, Brain PF (1992) Effects of sexand reproductive condition on nest building in fourspecies of rodents. The CEPNESP Bulletin 1, 2-8

Noirot E (1974) Nest-building by the virgin femalemouse exposed to ultrasound from inaccessiblepups. Animal Behaviour 22,410-20

Oley NN, Slotnick BM (1970) Nesting material as areinforcement for operant behavior in the rat.Psychonomic Science 21, 41-3

Porter WP, Busch RL (19781 Fractional factorialanalysis of growth and weaning success in Pero-myscus maniculatus. Science 202,907-10

Potgieter FJ, Wilke PI (1996) The dust content, dustgeneration, ammonia production, and absorptionproperties of three different rodent bedding types.Laboratory Animals 30, 79-97

Rajendram EA, Brain PF, Parmigiani S, Mainardi M(1987) Effects of ambient temperature on nestconstruction in four species of laboratory rodents.Boll. Zool. 54, 75-81

Roper TJ 119731Nesting material as a reinforcer forfemale mice. Animal Behaviour 2l, 733-40

Roper TJ (1975a) Diurnal rhythms in the nest-buildingbehaviour of female mice. Behaviour 52, 95-103

Roper TJ (1975b) Nest material and food as reinforcersfor fixed-ratio responding in mice. Learning andMotivation 6, 327-43

Roper TJ 11975c) Self-sustaining activities and re-inforcement in the nest building behaviour of mice.Behaviour 59, 40-57

Scharmann W (1991) Improved housing of mice, ratsand guineapigs: a contribution to the refinement ofanimal experiments. Alternatives to LaboratoryAnimals 19, 108-14

Schneider TE,Lynch CB (1984) Inve~,tigation of acommon physiological mechanism underlying pro-gesterone-induced and maternal nesting in miceMus musculus. Journal of Compa:rative Psychology98, 165-76

Schneider CW, Evans SK, Chenoweth MB, Beman FL(19731 Ethanol preference and behavioral tolerancein mice: biochemical and neurophysiological me-

Sherwin

chanisms. Journal of Comparative and Physiologi-cal Psychology 82, 466-74

Sherwin CM, Nicol CJ (1995) Changes in mealpatterning by mice measure the cost imposed bynatural obstacles. Applied Animal BehaviourScience 43, 291-300

Sherwin CM (1996a) Preferences of individuallyhoused TO strain laboratory mice for loose sub-strate or tubes for sleeping. Laboratory Animals 30,245-51

Sherwin CM 11996b) Laboratory mice persist ingaining access to resources: a method of assessingthe importance of environmental features. AppliedAnimal Behaviour Science 48, 203-14

Sherwin CM, Nicol CJ (1996) Reorganisation ofbehaviour in laboratory mice (Mus musculus 1withvarying cost of access to resources. AnimalBehaviour 51, 1087-93

Stephenson SK, Malik RC (1984) Energy partitioningand growth in mice selected for high and low bodyweight. Genetical Research 43, 323-37

van de Weerd HA, Baumans V, Koolhaas JM, vanZutphen LFM (19941 Strain specific behaviouralresponse to environmental enrichment in themouse. Tournal of Experimental Animal Science 36,117-27

Van Oortmerssen GA 11971) Biological significance,genetics and evolutionary origin of variability inbehaviour within and between inbred strains ofmice (Mus musculusl. Behaviour 38, 1-92

Veasey JS, Waran NKJ Young RJ (19961 On comparingthe behaviour of zoo housed animals with wildconspecifics as a welfare indicator. Animal Welfare5, 13-24

Voci VE, Carlson NR (1973) Enhancement of maternalbehaviour and nest building following systemic anddiencephalic administration of prolactin and pro-gesterone in the mouse. Tournal of Comparativeand Physiological Psychology 83, 388-93

Wainwright PE (1981) Maternal performance of inbredand hybrid laboratory mice (Mus musculus). Journalof Comparative and Physiological Psychology 95,694--707