Relative susceptibility of resident and transient Peromyscus subjected to weasel predation

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1 University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 1975 Relative susceptibility of resident and transient Peromyscus subjected to weasel predation Van Courtney Jamison The University of Montana Let us know how access to this document benefits you. Follow this and additional works at: Recommended Citation Jamison, Van Courtney, "Relative susceptibility of resident and transient Peromyscus subjected to weasel predation" (1975). Graduate Student Theses, Dissertations, & Professional Papers This Thesis is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact

2 RELATIVE SUSCEPTIBILITY OF RESIDENT AND TRANSIENT PEROMYSCUS SUBJECTED TO WEASEL PREDATION By Van C. Jam ison B.S., U n iv e rs ity o f W isconsin-m adison, 1971 P re se n te d in p a r t i a l f u lf illm e n t o f th e req u ire m e n ts fo r th e d eg ree o f M aster o f A rts UNIVERSITY OF MONTANA 1975 Approved by: C hairm an, Boardco/^ E xam iners G raduate School

3 UMI Number: EP37560 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMI Oissârtâtion PublisJ^ng UMI EP37560 Published by ProQuest LLC (2013). Copyright in the Dissertation held by the Author. Microform Edition ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Pro.Q^st* ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml

4 Jam iso n, Van C., M.A., June 1975 Zoology R e la tiv e S u s c e p tib ility of R e sid e n t and T ra n s ie n t Perom yscus S u b je c te d to W easel P re d a tio n (43 p p.) D ire c to r : Lee H. M etzgar Deer m ice (Perom yscus m an!c u la tu s) th a t had been f a m ilia r iz e d w ith one o f two la b o ra to ry e n c lo s u re s c o n ta in in g d i f f e r e n t h a b i t a t s were su b se q u e n tly s u b je c te d to s h o r t - t a i l e d w e asel (M ustela erm inea) p re d a tio n. H alf o f th e mice w ere exposed to p re d a tio n in th e e n c lo su re t h a t was f a m ilia r to them ( r e s i d e n t s ) ; th e o th e r h a lf were exposed to p re d a tio n in th e e n c lo su re th a t was n o t fa m ilia r to them ( t r a n s i e n t s ). Each t e s t c o n s is te d o f in tro d u c in g a s in g le d eer mouse in to one o f th e e n c lo s u r e s, w a itin g a s h o r t p e rio d, and th en p e rm ittin g a w e asel to e n te r. R e sid en t d e e r mice d isp la y e d a d i s t i n c t o v e r a ll advantage in te m p o ra rily a v o id in g w e asel p re d a tio n. On th e a v e ra g e, w e asels took 4.0 tim es as long to c a p tu re r e s id e n ts as t r a n s i e n t s. Two b e h a v io ra l d if f e r e n c e s betw een r e s id e n ts and t r a n s ie n ts a p p ear p r im a rily re s p o n s ib le fo r t h i s d i f f e r e n t i a l s u s c e p t i b i l i t y to p re d a tio n. F i r s t, th e w e asels seemed to have more d i f f i c u l t y lo c a tin g r e s i d e n t s, s e a rc h in g n e a rly tw ice as lo n g fo r r e s id e n ts as f o r t r a n s i e n t s. A lthough b o th r e s id e n ts and t r a n s i e n t s tended to change t h e i r b e h a v io r p a tte r n s a f t e r th e w e a s e l's r e l e a s e, t r a n s ie n ts s h i f t e d t h e i r b e h a v io r le s s fre q u e n tly th a n r e s id e n ts. Deer mice from b o th groups fro z e o r assumed an e lo n g a te p o s tu re and c re p t to a h ig h e r p o s itio n when a w easel began p a t r o l l i n g th e a re n a. Second, r e s id e n t d e e r mice e lu d e d th e w e a sels much more a d e p tly th an t r a n s ie n t d e e r m ice. The w e asels chased r e s id e n ts 17.0 tim es lo n g e r th an th ey chased t r a n s i e n t s. R e sid e n ts " e s caped" from th e w e a se ls 7.4 tim es more o fte n th a n t r a n s i e n t s. In e s c a p in g, r e s id e n t d e er mice f le d alo n g more to rtu o u s ro u te s th an t r a n s i e n t s. R e sid e n ts e x p lo ite d th e rock and v e g e ta tio n f e a tu r e s o f th e h a b ita t as th ey f le d ; t r a n s ie n ts d id n o t. Five r e s id e n ts p a sse d through th e n e s t boxes in f le e in g ; no t r a n s ie n t e n te re d th e n e s t. These b e h a v io ra l d if f e r e n c e s a re l ik e l y to in flu e n c e lo c a l p o p u la tio n dynamics th ro u g h d if f e r e n c e s in p re d a tio n m o r ta lity on r e s id e n ts and t r a n s i e n t s. i i

5 TABLE OF CONTENTS Page ABSTRACT... i i LIST OF FIGURES... v LIST OF T A B L E S... v i ACKNOWLEDGEMENTS...v i i C hapter I. INTRODUCTION... 1 I I. MATERIALS AND METHODS... 4 E x p erim en tal A p p a r a tu s... 4 L ab o ra to ry E n c lo su re s... 4 N est B o x e s... 6 Mouse I n j e c t o r s... 6 W easel H olding Cages and R unw ay-slide A p p aratu ses.. 8 O b serv a tio n S c r e e n s H a b ita ts w ith in th e A renas...10 A c q u is itio n and M aintenance o f A nim als...12 Form ation o f T e st P a i r s...14 E x p erim en tal P ro c e d u re s...16 W easel F eeding Schedule d u rin g th e E xperim ents M o d ific a tio n s in th e E x p erim ental A pparatus and D esign. 20 S t a t i s t i c a l R eferen ces I I I. R E S U L T S...22 S earch Times and Chase Times Numbers o f E s c a p e s D iffe re n c e s betw een T e st N ig h ts and A r e n a s...27 i i i

6 Page D e s c rip tio n s o f Deer Mouse B e h av io r B ehavior b e fo re th e W easels' R e le a s e B ehavior w h ile th e W easels S earched th e A renas E scape B e h a v io r IV. DISCUSSION...34 L o c a ta b lllty o f R e sid en t and T ra n s ie n t Deer Mice V u ln e ra b ility o f R e sid en t and T ra n s ie n t Deer Mice a f t e r D e te c tio n A p p lic a tio n s to F ie ld S i t u a t i o n s V. SUMMARY...41 LITERATURE CITED...43 Iv

7 LIST OF FIGURES F igu re Page 1. A P e rs p e c tiv e View o f th e L ab o ra to ry E n c lo su re s A Cut-away View o f th e Mouse I n j e c t o r The R unw ay-slide A pparatus t h a t Jo in e d th e W easel H olding Cage to th e A r e n a A Photograph o f th e H a b ita t w ith in th e Male A rena d u rin g th e F o u rth th ro u g h th e S ix te e n th S et o f T r ia ls.. * A Photograph o f th e H a b ita t w ith in th e Female Arena d u rin g th e F o u rth through th e S ix te e n th S et o f T r ia ls A D iagram m atic R e p re se n ta tio n o f th e T e st P ro ced u res in th e Male and Female A r e n a s...15

8 LIST OF TABLES T able Page 1. A Summary o f th e T e st Schedule and P re d a tio n D ata A sso c ia te d w ith th e R e sid en t and T ra n s ie n t Perom yscus T rie d in th e Male A rena A Summary o f th e T est Schedule and P re d a tio n D ata A sso c ia te d w ith th e R esid en t and T ra n s ie n t Perom yscus T rie d in th e Female A r e n a...25 v i

9 ACKNOWLEDGEMENT S 1 w ish to th an k my com m ittee chairm an, g ra d u a te a d v is o r, and f r ie n d. Dr. L, H. M etzgar, fo r h is encouragem ent, p a tie n c e, and guid an ce. He fu rn is h e d th e b a s ic e x p e rim e n ta l d e sig n and o ffe re d Im p o rta n t s u g g e stio n s to Im prove I t. Throughout t h i s s tu d y. Dr. M etzgar a s s i s t e d In th e p re p a ra tio n and observed each t r i a l. His c r itic is m s o f th e m an u scrip t w ere I n c is iv e. Where I was co n cern ed, he alw ays " k e p t th e f a i t h ". I w ish to th an k th e rem aining members o f my com m ittee, D rs. D. A. J e n n l, L. W, P e n g e lly, and P. L. W rig h t, f o r t h e i r many h e lp f u l su g g e stio n s and t h e i r e d i t o r i a l c r itic is m s o f th e m a n u scrip t. Dr. J e n n l 's l e t t e r o f encouragem ent p ro v id e d an I n s p i r a t i o n a l l i f t and was a p p re c ia te d. I w ish to th an k Mr. P. R. W aite I I I and my fe llo w g ra d u a te s tu d e n t, Ms. P. A. B a ird, f o r th e c o n tr ib u tio n s th ey made to th e com pletion o f t h i s p r o j e c t. They sh a re d t h e i r home w ith us th ro u g h o u t th e summer o f 1974, and, as f r ie n d s, c o n trib u te d s p i r i t u a l l y to d a lly l iv i n g. Fellow g rad u a te s tu d e n ts, M essrs. J. A. C ranford and D. H. Sm ith, ra n my tra p l in e s when I could n o t. Ms. Kae P a rk e r typed th e f i n a l m a n u scrip t. T h e ir a s s i s t a n c e, I d e a s, and su p p o rt w ere g r e a tly a p p re c ia te d. F i n a lly, my w if e, Mona, d e se rv e s a lo v in g "Thank you". She c o n tin u a lly I n s p ir e s my f e e lin g s f o r l i f e. F or a l l she I s and fo r a l l sh e hopes to becom e, I lo v e my "Shena Schm untee". v l l

10 CHAPTER I INTRODUCTION Most a d u lt d e e r mice (Perom yscus m a n ic u la tu s) I n h a b it home ranges th a t th e y seem to know w e ll (B u rt, 1940; B l a i r, 1940). A r e s i d e n t 's f a m i lia r ity w ith i t s home ran g e presum ably red u ces i t s s u s c e p t i b i l i t y to p re d a tio n (B u rt, 1940; B l a i r, 1951, 1953). F ie ld s tu d ie s on sm a ll mammal p o p u la tio n s re v e a l t h a t p e rio d s o f e m ig ra tio n o r in c re a s e d tr a n s ie n c e a re c h a r a c te riz e d by heavy p re d a tio n m o r ta lity ( B l a i r, 1953; E rrin g to n, 1964, 1967). These o b s e rv a tio n s su g g e st t h a t an im als t h a t have been d is p la c e d from o r have l e f t t h e i r home ran g es and a re wand e rin g th ro u g h u n fa m ilia r t e r r a i n may be more v u ln e ra b le to p re d a to rs th an r e s id e n ts. M etzgar (1967) exposed w h ite -fo o te d d e er mice (Perom yscus leucopus) t h a t he c o n sid e re d to be analogous to r e s id e n ts and t r a n s ie n ts to sc re e c h owl (Otus a s lo ) p re d a tio n in th e la b o r a to r y. He d em o n strated e x p e rim e n ta lly th a t th e sc re e c h ow l, an av ian p r e d a to r, c a p tu re s tr a n s i e n t mice more fre q u e n tly th a n r e s id e n ts. M etzgar p roposed th r e e d i s s i m i l a r i t i e s in r e s id e n t and t r a n s ie n t b e h a v io r t h a t co u ld account f o r t h i s d if f e r e n c e : F i r s t, r e s id e n t m ice may become aw are o f danger more r e a d ily.... Second, anim als th a t know th e t e r r a i n may escap e more e f f e c t i v e l y... T h ird, a t r a n s i e n t may be more a c tiv e and hence more exposed to p re d a tio n th a n a r e s id e n t.

11 2 Ambrose (1972) s u b je c te d meadow v o le s (M lcrotus p e n n sy lv a n lc u s) to b a m owl (T yto a lb a ) p re d a tio n and observed t h a t th e number o f " p re d a to r h o u rs p e r v o le e a te n " was s i g n i f i c a n t l y h ig h e r f o r r e s id e n t th a n fo r t r a n s ie n t v o le s. He confirm ed M etzgar*s c o n te n tio n th a t r e s id e n t anim als d e riv e a c o n s id e ra b le advantage from r e s t r i c t i n g t h e i r a c t i v i t i e s to a f a m ilia r home range s in c e t r a n s ie n ts a re more s u s c e p tib le to p r e d a to r s. However, Ambrose d id n o t f e e l t h a t a l l o f th e b e h a v io ra l d if f e r e n c e s M etzgar proposed to account f o r t h i s adv antage a p p lie d in th e case o f M ic ro tu s. He argued t h a t b ecau se meadow v o le s use runways e x te n s iv e ly, n e ith e r r e s id e n t n o r t r a n s i e n t v o le s a re w e ll adap ted to r e a d ily d e te c t an a v ia n p r e d a to r. Ambrose reaso n ed t h a t th e o p p o rtu n ity a r e s id e n t o r t r a n s ie n t had to d ecid e on an e f f e c t i v e escap e ro u te would be s e v e re ly lim ite d as a consequence. Ambrose in d ic a te d t h a t he had found t r a n s ie n t meadow v o le s w ere n o rm ally more a c tiv e th an r e s id e n ts and concluded th a t M etzgar*s t h i r d s u g g e stio n p ro b ab ly p ro v id ed th e b e s t e x p la n a tio n o f th e advantage r e s id e n t v o le s h ave. I exposed d e e r mice (Perom yscus m a n ic u la tu s) to s h o r t - t a i l e d w e a se ls (M ustela erm inea) i n a la b o ra to ry e n c lo s u re and endeavored t o : 1. d eterm in e w h eth er f a m i lia r ity w ith a s p e c i f i c h a b ita t in c re a s e s th e p r o b a b ility o f s u r v iv a l when Perom yscus e n co u n ter non- a v ia n p r e d a to r s. The p re v io u s s tu d ie s re g a rd in g th e e f f e c t s o f h a b i t a t f a m i l i a r i t y on p re d a tio n r a t e s have d e a lt s t r i c t l y w ith r a p t o r i a l p re d a to rs 2. o b serv e th e b e h a v io r o f r e s id e n t and t r a n s i e n t Perom yscus i n th e p re sen c e o f a p re d a to r to d eterm in e w h eth er any o f th e b e -

12 3 h a v lo r a l d i s s i m i l a r i t i e s th a t w ere proposed by M etzgar le a d to a low er s u s c e p t i b i l i t y among r e s id e n ts 3. d e s c rib e r e s id e n t and t r a n s ie n t Perom yscus b e h a v io r d u rin g t h e i r e n c o u n te rs w ith s h o r t - t a i l e d w e a s e ls.

13 CHAPTER I I MATERIALS AND METHODS Deer mice (Perom yscus m an icu la tu s) w ere f a m ilia r iz e d w ith one o f two la b o ra to ry a re n a s and su b seq u e n tly s u b je c te d to p re d a tio n by s h o r t - t a i l e d w e asels (M ustela erm inea). Each t e s t in v o lv e d in tro d u c in g a s in g le d e e r mouse in to an a re n a, w a itin g a s h o rt p e rio d, and th e n p e rm ittin g a w e a se l to e n te r. The tim e tak e n by th e w easel to c a p tu re th e mouse and v a rio u s components o f t h i s p re d a tio n w ere re c o rd e d. L a b o ra to ry E n clo su re s E x p erim ental A pparatus Two i d e n t i c a l w ire mesh e n c lo su re s (Im x Xm x 2m long) se rv e d as a re n a s f o r th e stu d y (F ig. 1 ), The wooden fram es c o n s is te d o f "tw o-by-tw os" jo in e d in a re c ta n g u la r fa s h io n. At th e b a se o f th e fram e s, each j o i n t was re in f o r c e d by a n g u la r c o m e r b ra c e s. e n t i r e fram e was o v e rla id w ith h a lf - in c h w ire mesh s c re e n in g. The A p a i r o f 10cm x 10cm openings jo in e d th e r e s p e c tiv e a re n a s w ith a w easel n e s t box and w ith a mouse i n j e c t o r. A 16cm s t r i p o f g a l v a n iz ed f la s h in g c ir c le d th e in s id e o f th e e n c lo s u re s 50cm above th e a re n a f lo o r to reduce a ccess to th e c e i lin g by th e m ice. A 5cm d ep th o f wood c h ip s was sm oothed o v er th e f lo o r o f each enc lo s u re. A s in g le n e s t box was i n s t a l l e d in b o th a re n a s. V isu a l 4

14 F ig. 1. A p e rs p e c tiv e view o f th e la b o r a to r y e n c lo s u r e s, OS. WC. The o b se rv a tio n sc re e n s w ere c o n s tru c te d by s t r e t c h i n g a double bed s iz e d s h e e t o v er 2.3m x 1.5m wooden fram e s. The s h e e ts w ere dyed cocoa brown. The w easel h o ld in g c a g e s, 19cm x 23cm x 77cm lo n g, cons i s t e d o f a 19cm x 23cm x 35cm n e s tin g a re a and a 19cm X 23cm X 42cm w ire mesh e x e r c is e e n c lo s u re. VS. H a lf-in c h plywood s c re e n. RS. R unw ay-slide a p p a ra tu s. See F ig. 3. ND. The mouse n e s t box, 16cm x 18cm x 13cm h ig h, c o n ta in e d a sim ple la b y r in th th a t was form ed by two 12cm x 12cm q u a rte r-in c h plywood p a n e ls. CB, "Two-by-two" r e in f o r c in g a n g u la r c o m e r b r a c e s. MI. Mouse i n j e c t o r. See F ig. 2. AS. Aluminum, s h e e tin g.

15

16 6 c o n ta c t betw een th e a re n a s was p r o h ib ite d by aluminum s h e e tin g th a t covered one end o f each e n c lo su re (F ig. 1 ). N est Boxes The n e s t boxes w ith in each e n c lo su re w ere c o n s tru c te d from q u a r te r - in c h plywood (F ig. 1 ). Two 4cm x 4cm e n tra n c e s w ere p o s i tio n e d d ia g o n a lly on o p p o site s id e s o f each n e s t box. A p a i r o f plywood p a n e ls formed a sim p le la b y r in th w ith in each box and th e to p s w ere h in g ed to f a c i l i t a t e c le a n in g. Mouse I n je c to r s The mouse I n j e c to r s c o n s is te d o f two com ponents; a ch an n el and a s l i d i n g p lu n g e r. The chan n el In clu d e d an open h o u sin g c u b ic le a t th e end t h a t was a tta c h e d to th e a re n a and a guide f o r th e s l i d i n g p lu n g e r a t th e o p p o site end (F ig, 2 ). A 61cm le n g th o f "tw o -b y -fo u r" was u t i l i z e d as a b a se f o r th e channel s t r u c tu r e. S e c tio n s o f one-in ch p in e b o ard formed th e s id e s and th e ro o f. Guide grooves were c u t In th e h o u sin g c u b ic le 3.5cm from th e end a d jo in in g th e a re n a. A p re s se d -b o a rd g a te was I n s e r te d I n to th e s e g ro o v e s, c lo s in g t h a t end o f th e c u b ic le. The p lu n g e r was c o n s tru c te d from th r e e p ie c e s o f o n e -in c h p in e b o a rd ; a 31cm b a se and 9.5cm x 8.5cm p a n e ls jo in e d to o p p o s ite ends o f th e b a s e. Each p lu n g e r was p a sse d th ro u g h th e end o f th e h o u sin g c u b ic le f a r t h e s t from th e a re n a so t h a t th e b a se o f th e p lu n g e r r e s te d In th e guide and th e le a d in g p lu n g e r p a n e l b lo ck e d th e f a r end o f th e c u b ic le. As a consequence, a mouse e n c lo su re was c re a te d a d ja c e n t to th e a re n a. The forw ard edge o f th e p lu n g e r was b e v e le d and a l l s l i d in g s u r fa c e s w ere sanded and t r e a te d w ith

17 F ig, 2, A cut-aw ay view o f th e mouse I n j e c t o r, ME, The mouse e n c lo s u re, 9cm x 10cm x 15cm lo n g, t h a t was formed by th e s l i d in g p lu n g e r and th e chan n el s t r u c t u r e o f th e i n j e c t o r. SP, The s l i d in g p lu n g e r. CSG. The b ase o f th e channel s t r u c tu r e t h a t guided th e s l i d in g p lu n g e r, PEG, The p re s se d -b o a rd g a te, 11cm X 14cm h ig h, was p e r f o r a te d w ith q u a rte r -in c h h o le s. PS, Q u a rte r-in c h c lo th e s l i n e t h a t was dyed cocoa brown and th re a d e d through th e p u lle y system.

18 CSG Alt

19 Dupont Dry L u b ric a n t to reduce f r i c t i o n and n o is e. 8 P r i o r to a t e s t, a mouse was p la c e d In th e mouse e n c lo su re o f each I n j e c t o r. The e n t i r e mouse I n j e c to r was th e n a tta c h e d to one o f th e two a re n a s. Each mouse was I n je c te d I n to I t s r e s p e c tiv e are n a by slo w ly r a i s in g th e p re s se d -b o a rd g a te and advancing th e p lu n g e r tow ard th e a re n a. When a mouse had e n te re d th e a re n a th e g a te was low ered b eh in d I t, W easel H olding Cages and R unw ay-slide A pparatuses W easels w ere m a in tain ed In h o ld in g cages t h a t c o n s is te d o f a n e s t box c o n s tru c te d from o n e-in ch p in e b o ard and a h a lf - in c h w ire mesh e x e r c is e e n c lo su re (F ig. 1) A w e a s e l's a c c e ss to th e p re d a tio n a re n a could be re g u la te d v ia a ru n w a y -slid e a p p a ra tu s jo in in g th e h o ld in g cage w ith th e a re n a (F ig. 3 ). O ne-inch p in e b o ard was a tta c h e d to th e to p and bottom o f "tw o -b y -fo u r s id e p a n e ls to form a runway t h a t was 15cm h ig h and 6.5cm w ide. At m id length a v e r t i c a l groove, 2cm w ide and 2.5cm d e ep, was c h is e le d I n to each s id e p a n e l. I n l a i d w ith s e c tio n s o f autom obile window g u id e. These grooves w ere T his guide m ater i a l se rv e d as a channel f o r th e s l i d in g g a te and muted I t s o p eratio n. A le n g th o f h a lf - in c h an g le Iro n was p o s itio n e d on e i t h e r s id e o f th e grooves to p re v e n t anim als from u r in a tin g o r d e fe c a tin g d i r e c t l y on th e guide mechanism. S o lid p re s se d -b o a rd s l i d e s w e ig h te d w ith le a d w ere s lip p e d I n to th e g u id e s. Plywood sc re e n s w ere p la c e d betw een th e h o ld in g cages and th e p re d a tio n a re n as (F ig. 1 ). The w e asels w ere re le a s e d by l i f t i n g th e w eig h ted s l i d e s.

20 F ig. 3. The ru n w a y -slid e a p p a ra tu s t h a t jo in e d th e w easel h o ld in g cage to th e a re n a. a. Cut-away view, AWG. 9cm s e c tio n s o f autom obile window g u id e. AI. 9cm le n g th s o f h a lf - in c h a n g le ir o n. SWG. S o lid p re s se d -b o a rd g a te w eighted w ith 2% pounds o f le a d. PS. Q u a rte r-in c h c lo th e s l in e t h a t was dyed cocoa brown and th re a d e d t h r o u ^ th e p u lle y sy stem. b. Top view.

21 a. PS SWG AI AWG b. AWG Al -SWG Al m AWG

22 10 Both w e a se ls responded r a p id ly to th e open g a te and e n te re d th e a re n a w ith o u t h e s i t a t i n g. A fte r a w easel had e n te re d th e a re n a, th e s l i d e was low ered b ehin d i t slo w ly. O b serv a tio n S creens I n d iv id u a l s l i d e m echanism s, i. e., th e mouse i n j e c t o r g a te, th e p lu n g e r p o r tio n o f th e mouse i n j e c t o r, and th e ru n w a y -slid e, w ere o p e ra te d from b eh in d th e o b s e rv a tio n sc re e n s by means o f an overhead p u lle y system. Q u a rte r-in c h c lo th e s l in e was th re a d e d th ro u g h t h i s w e ll o ile d p u lle y a p p a ra tu s. An o b s e rv a tio n sc re e n was p la c e d n e x t to each la b o ra to ry e n c lo su re a c ro s s from th e mouse i n j e c t o r (F ig. 1 ), A p a i r o f 16cm X 7cm o b s e rv a tio n p e e p s, an upper one (2.0m above th e f lo o r) and a low er one (1.4m above th e f l o o r ), w ere opened n e a r th e v e r t i c a l m id lin e o f each s c re e n. A s te p la d d e r was employed fo r th e o b s e rv a tio n s t h a t w ere reco rd ed from th e upper peep. D uring each t e s t, I clim bed th e s te p la d d e r to th e upper o b se rv a tio n peep and M etzgar sto o d a t th e low er one. We observed each t r i a l from th e s e p o s itio n s. H a b ita ts w ith in th e Arenas D is t i n c t l y d i f f e r e n t h a b ita t s w ere la id o u t in th e two e x p e rim en tal a re n a s. In one a re n a l e a f l e s s ap p le (Malus s p.) and R ussian- o liv e (E laeagnus a n g u s tif o lia ) b ran ches w ere ta n g le d to s im u la te a low b ru sh y h a b ita t w ith d iv e rs e a e r i a l runways (F ig. 4 ). For conv e n ie n c e, t h i s a re n a w i l l be r e f e r r e d to as th e "m ale arena" b e cau se a l l male mice w ere te s te d in t h i s e n c lo s u re a g a in s t th e same m ale w e a sel. The o th e r e n c lo su re was s u p p lie d w ith num erous, ra n -

23 11 F ig, 4. A photograph o f th e h a b ita t w ith in th e m ale arena d u rin g th e fo u rth th rough th e s ix te e n th s e t o f t r i a l s

24

25 12 domly p la c e d s to n e s, and a few l e a f l e s s R u s s ia n -o liv e b ran c h es t h a t w ere propped a g a in s t th e w ire mesh (F ig. 5 ). T his a re n a w i l l be r e f e r r e d to as th e "fem ale aren a" b ecau se a l l fem ale mice were t e s te d in t h i s e n c lo su re a g a in s t th e same fem ale w e a se l. N est boxes w ere i n s t a l l e d in com parable p o s itio n s except t h a t th e n e s t box in th e male a re n a was e le v a te d 20cm above th e a re n a f lo o r w h ile th e o th e r n e s t box r e s te d on th e s u b s tr a te. A 2 5 -w att re d l i g h t bulb illu m in a te d each a re n a. One l i g h t was s itu a te d d i r e c t l y above th e c e n te r o f th e male a re n a a t a h e ig h t o f 175cm. The o th e r was s u s pended o v e r th e w easel h o ld in g cage th a t was a tta c h e d to th e fem ale a re n a ; 8cm to th e s id e o f th e a re n a a t a h e ig h t o f 90cm. A 15:9 hour l i g h t : dark regim e was m ain tain ed in th e la b o ra to r y. T h is sc h ed u le was n o t sy n c h ro n ized w ith th e p r e v a ilin g lo c a l photop e rio d. The l i g h t p e rio d began a t 1200hr; th e dark p e rio d a t 0300hr. The 2 5 -w a tt red l i g h t s rem ained on a t a l l tim e s. A c q u is itio n and M aintenance o f Animals L iv e, w ild -b o m d e er mice (Perom yscus m an icu la tu s) w ere o b ta in e d from v a rio u s in d iv id u a ls engaged in sm a ll mammal tra p p in g in th e M isso u la a re a. No d a ta on th e h a b ita t ty p e o r th e s p e c if ic a re a w ith in w hich an anim al was tra p p e d w ere re c o rd e d. F ie ld -tra p p e d mice w ere re tu rn e d to th e la b o ra to ry and p a ir e d ; one male and one fem ale p e r cag e. Each p a i r o f mice was k e p t in a 13cm x 15cm x 29cm h o ld in g cage and p ro v id ed w ith P u rin a L ab o ra to ry Chow and w a te r ^ lib itu m. Mouse p a ir s w ere s u b je c te d to th e 15:9 h o u r l ig h t ; d a r k regim e f o r a t l e a s t one week p r i o r to t e s t i n g.

26 13 F ig. 5. A photograph o f th e h a b i t a t w ith in th e fem ale a re n a d u rin g th e fo u rth th ro u g h th e s ix te e n th s e t o f t r i a l s.

27 f m

28 14 Two la b -b o m s h o r t - t a i l e d w easels (M ustela erm ine a) a male and a fem ale, w ere p u rch ased from th e U n iv e rs ity o f Idaho a t Moscow. These anim als w ere k e p t in s e p a ra te h o ld in g cag es. P r io r to th e e x p e rim e n ts, each w easel was s u p p lie d w ith one l iv e la b o ra to ry mouse d a ily and a w eekly v ita m in supplem ent. F resh w a ter was a v a ila b le c o n tin u a lly. Both w e asels r e ta in e d t h e i r summer p e la g e th ro u g h o u t th e stu d y. Form ation o f T e s t P a ir s The e x p e rim e n ta l com parison o f p re d a tio n on r e s id e n t and tr a n s i e n t Perom yscus was o rg an iz ed around " t e s t p a i r s ". Each t e s t p a ir c o n s is te d o f two male o r two fem ale d e e r m ice. Each p a ir in c lu d e d a r e s id e n t and a t r a n s ie n t anim al o f th e same se x. The two mice form ing a t e s t p a i r were t r i e d a g a in s t th e same w easel in th e same a re n a on two c o n se c u tiv e n ig h ts. F ive n ig h ts were re q u ire d fo r each s e t o f t e s t s (F ig. 6 ). Mice w ere allo w ed th re e f u l l n ig h ts to f a m ilia r iz e them selves w ith one o f th e a re n a s. P r io r to N ight 4, th r e e liv e tr a p s were p la c e d in each a re n a. L ive tr a p s rem ained in th e a re n a s th ro u g h o u t th e f i r s t h a lf o f N ig h t 4. D uring th e second h a lf o f N ight 4 (T est N ight One) a r e s id e n t male and a t r a n s ie n t fem ale o r a t r a n s ie n t male and a r e s i d ent fem ale were t e s te d. The t e s t p a i r complements to th e anim als t r i e d on T e s t N ight One were t e s te d d u rin g th e second h a lf o f th e fo llo w in g n ig h t (T est N ight Two). For exam ple, i f a r e s id e n t male and a t r a n s i e n t fem ale were t r i e d on T est N ight One, a t r a n s ie n t m ale and a r e s id e n t fem ale w ere te s te d on T e st N ig h t Two. A t e s t p a ir c o n s is te d o f a r e s id e n t and a tr a n s ie n t male o r a

29 15 F ig. 6. A diagram m atic r e p r e s e n ta tio n o f th e t e s t p ro cedures in th e male and fem ale a re n a s. T e st e v e n ts in th e two a re n a s o c cu rred c o n c u rre n tly. T e st p a i r s alw ays c o n s is te d o f male p a ire d w ith m ale^ and fem ale^ p a ire d w ith female. The o rd e r in w hich th e s e anim als were t e s t e d changed betw een su c c e s s iv e s e ts o f t e s t s.

30 MALE ARENA (M) FEMALE ARENA (F) NIGHT! HABITAT FAMILIARIZATION PERIOD f o r a p a ir o f m ic e MALE'^A FEMALE" NIGHT2 HABITAT FAMILIARIZATION PERIOD f o r a p o i r o f m k e MALE' & FEMALE' NIGHT3 LIVE TRAPPING & REMOVAL TEST NIGHT ONE resident ma!e' br transient matet NIGHT4 >'rr.?.. TEST NIGHT.ONE. ; transient. fêmalé'j or resident fem ale'» TEST NIGHT TWO transient male*or resident male*^ NIGHTS TfST NIGHT resident female; or si ; transient fem ale? V*'

31 16 re sid e n t and a tra n s ie n t female. Resident males were fa m ilia r w ith the male arena and were te s te d in the male arena. T ransient males were fa m ilia r w ith the female arena and were tr ie d in the male arena. S im ila rly, re sid e n t females were fa m ilia r w ith the female arena and were te s te d in the female arena. T ransient females were fa m ilia r w ith the male arena and were tr ie d in the female arena. The sequence in which t e s t p a irs were tr ie d was reversed between successive se ts of t e s ts. Thus, i f a resid en t male and a tra n s ie n t female were tr ie d on Test Night One of a s p e c ific s e t of t e s t s, a tra n s ie n t male and a re sid e n t female were tr ie d on Test Night One of the ensuing s e t of t e s ts. This design furnished p a ire d data th a t was unbiased w ith resp ect to the n ig h t of te s tin g, the weasel p red ato r employed, and the sex of the mouse te s te d. Experim ental Procedures The b a sic experim ental procedures th a t were employed remained constant throughout the study. However, when minor changes appeared to be a p p ro p ria te, they were incorporated in to the scheme. The f in a l experim ental technique rep re se n ts the r e s u lt of th is evolutionary pro cess. Procedural m odifications w ill be explained follow ing a complete d e sc rip tio n of the f in a l technique. Two mice, a p aired male and fem ale, were rele ased in to each arena a t approxim ately 1930hr. These mice were allowed th ree f u ll n ig h ts to fa m ilia riz e them selves w ith th e ir surroundings. At 1900hr, before the onset of Night 4, th ree 3in x 3^in x 9in Sherman c o llap s-

32 17 Ib le liv e trap s were se t in each arena. The mice and these trap s were removed from the arenas one hour p rio r to the te s ts conducted on T est Night One. In every in sta n c e, both p a irs of mice were captured. A ll te s ts were made between 0700hr and 0930hr. Immediately a f te r removal, each p a ir of mice was returned to the holding cage th a t the p a ir had occupied b efo re being introduced in to the arena. Food and w ater were a v a ila b le in the holding cages ad lib itu m. The p a ir of mice to be tr ie d on Test Night One remained in th e ir holding cage fo r ten m inutes. A fter th is period, each member of the p a ir was tra n s fe rre d to one of the mouse in je c to r s. The mouse in je c to r containing the male mouse was subsequently attached to the male arena. The in je c to r housing the female was jo in ed to the female arena. Because both of the te s t mice were familiar w ith the same arena, the mouse th a t was in tro duced in to the neighboring arena became a tra n s ie n t. Male mice were l e f t in the in je c to rs for 30 minutes to allow them to recover from any trauma they might have experienced during handling. A fter w aitin g 30 m inutes, the observers p o sitio n ed themselves behind the observation screen adjacent to the male arena. Male mice were always tr ie d b efore female mice. When the observers* eyes had become accustomed to the darkness, the male mouse was in je c te d in to the arena. This mouse was observed fo r 5 m inutes, then the male w easel was rele ased and the t r i a l began. We recorded four q u a n tita tiv e measures during each t r i a l ; 1. T otal time to c a p tu re, the amount of time th a t elapsed between the re le a se of the w easel and the moment the mouse was captured. T o tal time to capture is the sum of search time and

33 18 chase time 2, Search tim e, the amount of time th a t elapsed between the re le a se of the w easel and the point the w easel appeared to lo cate the mouse 3, Chase tim e, the time i t took a weasel to capture a mouse once i t had lo cated i t 4, Number of escap es, any manuever th a t broke o ff a continuous chase and caused the w easel to resume searching. A fter capturing the mouse, the weasel was returned to i t s holding cage. Then, the observers moved behind the observation screen next to the female arena and repeated the sequence. Female mice remained in the mouse in je c to rs from minutes depending on the length of the male t e s ts. I wrote b eh av io ral d e scrip tio n s of the events th a t we observed during the t r i a l s immediately a fte r each t e s t n ig h t. The remaining p a ir of mice, t e s t p a ir complements to the animals tr ie d on T est Night One, in h ab ited th e ir holding cage u n til the follow ing n ig h t. T est Night Two. The te s t procedure during Test Night Two was id e n tic a l to th a t used on Test Night One. A fter each se t of t r i a l s, both w easels were tra n s fe rre d to clean holding cages containing fresh cotton n e stin g m ateria l. Wood chips and fe c a l waste were brushed from the runw ay-slide mechanisms, the mouse in je c to r s, and the mouse n e st boxes. The cotton n e stin g m a te ria l in both of the mouse n e st boxes was changed. When these p rep a ratio n s were completed, d iffe re n t p a irs of m ice, one male p a ire d w ith one fem ale, were released in to each arena and the e n tire experim ental procedure was repeated.

34 Weasel Feeding Schedule during the Experiments 19 The w easels followed a rig id feeding regime throughout each s e t of t e s t s. Each w easel received one liv e lab o rato ry mouse d aily a t 1400hr during the th ree night m ouse-fam iliarization period. Uneaten remains from the previous n ig h t's feeding were removed a t th is tim e. An attem pt was made to obtain the same, unsated n u tr itiv e s ta te in each weasel on T est Night One and Test Night Two. Thus, a t I200hr, follow ing the th ird n ig h t of fa m ilia riz a tio n, the remains from the preceding day were removed, but no new food was added. Both w easels were deprived of food for the next 7 hours. At 1900hr, before p lacin g the liv e trap s in the a re n a s, each weasel was supp lie d w ith one liv e lab o rato ry mouse. p o rtio n s of these mice were removed. One hour l a t e r, the uneaten Both weasels were deprived of food fo r the next 11-13^ hours u n til the t r i a l s were conducted on Test Night One, The w easels were allowed to keep the te s t mice th a t they captured u n til 1200hr. At th a t tim e, the remains of the t e s t mice were removed from the weasel holding cages. Both weasels were deprived of food fo r the next 7 hours. At 1900hr, each weasel received one liv e lab o rato ry mouse. One hour l a t e r, the uneaten portio n s were removed- Both w easels were again deprived of food u n til the t r i a l s were conducted on Test Night Two. The weasels were perm itted to keep these t e s t mice a lso. I a n tic ip a te d th a t th is feeding schedule would provide nearly id e n tic a l n u tr itiv e s ta te s on Test Night One and Test Night Two. However, i f c o n siste n t d ifferen c e s in the n u tr itio n a l s ta te s of the w easels did a ris e from th is feeding schedule, th e ir e ffe c ts were

35 elim in ated through time by sw itching the order in which re sid e n t and tra n s ie n t animals were te s te d on successive se ts of te s ts. 20 M odifications in the Experimental Apparatus and Design Some p o rtio n s of the apparatus used during the f i r s t e ig h t se ts of t r i a l s were deemed u n sa tis fa c to ry. These components were a lte re d a t various times during these e a rly t r i a l s to form the f in a l appara tu s. Throughout the f i r s t e ig h t s e ts of t r i a l s, brown wrapping paper was stre tc h e d over both observation screens and burlap ra th e r than aluminum sh eetin g was used to o b stru ct v isu a l contact between the are n as. During th is tim e, d if f e r e n t, n o is ie r, runway-slide mechanisms were used and fo r the f i r s t th ree se ts of t r i a l s, the slid e s were not weighted. The male arena contained fewer branches and the female arena lacked stones for the f i r s t th ree s e ts of t r i a l s. In ad d itio n, the 25-watt red lig h ts were located in d iffe re n t p o sitio n s and cumbersome hand-held le v e rs, ra th e r than p u lle y s, were used to operate the s lid in g mechanisms during the f i r s t th ree se ts of t r i a l s. Only one change in the apparatus occurred during the la s t eleven s e ts of t r i a l s. P rio r to the seventeenth s e t of t r i a l s, the wood chips were vacuumed from the flo o rs of both arenas and new chips were smoothed over each flo o r. The h a b ita ts in the male and the female arenas were subsequently rearranged using the same mater i a l s in the resp ec tiv e arenas. The n e st box in the female arena was e le v ated w hile the one in the male arena was lowered to the arena flo o r. Procedural changes were made throughout the experim ent. During the f i r s t e ig h t se ts of t r i a l s, te s t mice were observed fo r one

36 21 m inute, ra th e r than five m inutes, p r io r to the re le a se of the w easels, and only one q u a n tita tiv e measure, t o t a l time to capture, was recorded. Between the fourth and the eighth se ts of t r i a l s, mouse p a irs were allowed a sin g le f u l l night to fa m ilia riz e themselv es w ith th e ir resp ec tiv e arenas and no behavioral d e scrip tio n s were w ritte n. P rio r to the tw elfth se t of t r i a l s, the mice tr ie d on Test Night One were not placed in th e ir holding cages before being tra n s fe rre d to the mouse In je c to rs. In ste ad, these te s t mice were tran sm itte d d ire c tly to the mouse in je c to rs from the liv e tra p s. During the f i r s t th irte e n se ts of t r i a l s, the weasels were only deprived of food fo r one hour p rio r to a te s t n ig h t. They received one liv e lab o rato ry mouse d a ily. A ll changes in the experim ental design and the apparatus were made between s e ts of t e s ts. No m odifications were introduced during any one sin g le se t of t e s ts. As a consequence, members of a t e s t p a ir were always comparable. S t a t i s t i c a l References The s t a t i s t i c a l te s ts th a t I applied to the data are presented by S iegel (1956). O ne-tailed te s ts of the hypotheses were employed whenever the d ire c tio n of the d ifferen c e had been p red icted.

37 CHAPTER I I I RESULTS R esident Peromyscus are le ss vulnerable to weasel predation than tra n s ie n t Peromyscus. The mean t o t a l time to capture of re sid e n ts (x=228,3 seconds) is 4.0 times g re a te r than the mean t o t a l time to capture of tra n s ie n ts (x=57.8 seconds). Pooling the data from both arenas (Tables la, IB and 2A, 2B), the t o ta l times to capture of re sid e n t mice are s ig n ific a n tly g re a te r than the to ta l tim es to capture of tra n s ie n t mice (p <.0 0 5, Wilcoxon M atched-pairs Signed-Ranks T est, o n e -ta ile d ). The re s u lts are id e n tic a l when each arena is analyzed se p ara tely (each, p <.0 0 5, Wilcoxon Matched- P a irs Signed-Ranks T est, o n e -ta ile d ). Search Times and Chase Times Analyses of the components of t o t a l time to capture in d ic a te th a t re sid e n ts avoid d etectio n more e ffe c tiv e ly and, a f te r being discovered, elude the w easels much more adeptly than tra n s ie n ts. The g re a te r share of the d ifferen c e between resid en t and tra n s ie n t t o t a l tim es to capture a ris e s from an enormous d isp a rity in the chase tim es of re s id e n ts and tra n s ie n ts. The mean chase time of re s id e n ts (x=197.3 seconds) i s 17.0 tim es g re a te r than the mean chase time of tra n s ie n ts (x=11.6 seconds). Resident chase times are s ig n ific a n tly g re a te r than tra n s ie n t chase times when the data from both arenas are pooled and when each arena is tre a te d in d i- 22

38 23 TABLE 1 A SUMMARY OF THE TEST SCHEDULE AND PREDATION DATA ASSOCIATED WITH THE RESIDENT AND TRANSIENT PEROMYSCUS TRIED IN THE MALE ARENA A. Residents Number of Test Night T otal Time Search Chase Number of Test Set T ried to Capture Time Time Escapes (seconds) (seconds) (seconds) «« Means

39 24 TABLE 1-Continued B. T ransients Number of Test Set Test Night T ried T o tal Time to Capture (seconds) Search Time (seconds) Chase Time (seconds) Number of Escapes Means

40 25 TABLE 2 A SUMMARY OF THE TEST SCHEDULE AND PREDATION DATA ASSOCIATED WITH THE RESIDENT AND TRANSIENT PEROMYSCUS TRIED IN THE FEMALE ARENA A. R esidents Number of Test Set T est Night Tried T otal Time to Capture (seconds) Search Time (seconds) Chase Time (seconds) Number of Escapes Means

41 26 TABLE 2-Continued B, T ransients Number of Test Set Test Night T ried T otal Time to Capture (seconds) Search Time (seconds) Chase Time (seconds) Number of Escapes * « « Means

42 27 v ld u a lly ( a l l, p <,025, Wilcoxon M atched-pairs Signed-Ranks T est, o n e -ta ile d ). D ifferences in re sid e n t and tra n s ie n t search times (search tim es fo r re sid e n t and tra n s ie n t te s ts ) have a minor e ffe c t on the t o t a l time d iffe re n c e s. The mean search time fo r re sid e n t mice (x=127,2 seconds) i s 1,7 times g re a te r than the mean search time fo r tra n s ie n ts (x=75,5 seconds). However, th ere is no s ig n ific a n t d ifferen c e between the search tim es when the data from each arena are pooled and when they are analyzed se p ara tely (,6 0 < p <,8 6, Wilcoxon M atched-pairs Signed-Ranks T e st), Numbers of Escapes R esidents escaped 7,4 tim es more frequently than tra n s ie n ts. The numbers of escapes of re sid e n t mice are s ig n ific a n tly g re a te r than the numbers of escapes of tra n s ie n t mice fo r the data from both arenas (p <.0 0 5, Wilcoxon M atched-pairs Signed-Ranks T est, o n e -ta ile d ). The re s u lts obtained by ev alu atin g each arena in d i v id u ally are sim ila r (each, p <.0 2 5, Wilcoxon M atched-pairs Signed- Ranks T e st, o n e -ta ile d ). D ifferences between T est Nights and Arenas Resident and tra n s ie n t t o ta l tim es to capture, search tim es, chase tim es, and numbers of escapes are not s ig n ific a n tly d iffe re n t between the two arenas (,1 8 < p <,9 8, Mann-Whitncy U T e st), or between T est Night One and Test Night Two (,0 6 < p <,9 4, Mann-Whitney U T e st). The t e s t n ig h t (Test Night One versus Test Night Two), mouse sex, w easel sex, and arena environment had no d e te ctab le e ffe c t on the experim ental re s u lts.

43 28 D escriptions of Deer Mouse Behavior E lsenberg (1962,1968) described Peromyscus behavior In d e ta il. Although the lig h tin g fo r my experiment r e s tr ic te d observations to the most e a s ily d isc e rn ib le aspects of deer mouse behavior, the behavior p a tte rn s th a t were seen corresponded to Elsenberg*s des c rip tio n s. Elsenberg* s names fo r the postu res and b ehavioral p a tte rn s of Peromyscus are used In the follow ing se c tio n. Prey behavior can be divided In to th ree d isc re te periods of a c tiv ity ; a fiv e minute period p r io r to the re le a se of the w easels, a search p e rio d, and a chase period. Behavior before the Weasels* Release R esident Peromyscus h e s ita te d momentarily In an elongate postu re as they emerged from the mouse In je c to r. T heir body contours became rounded, qu ick ly, as they advanced Into the arena. Therea f t e r, they moved a c tiv e ly about the e n tire arena In a relaxed In v e stig a to ry p o stu re. During the fiv e minute period p rio r to the re le a se of the w easels, five of tw enty-eight re sid e n ts fed and two others drank. T ran sien ts lo ite re d at the mouth of the In je c to r In an elongate p o stu re for considerable periods of tim e. They probed the arena through a s e rie s of e r r a t ic advances th a t o rig in a te d at the In je c to r. T ran sien ts moved from the In je c to r In an elongate postu r e, advanced sp o ra d ic a lly, and In te rru p te d t h e ir movements by free zin g p e rio d ic a lly. T ransients th a t had ventured Into the arena re g u la rly turned In place and dashed back to the area Immed ia te ly In fro n t o f the In je c to r. With tim e, tran sie n ts* body

44 29 contours became rounded and each successive advance in to the arena became longer. This behavior was repeated c o n siste n tly u n til the w easels were released. T ransients never in te rru p te d th e ir exploratory a c t iv i t ie s to feed or drink. S p a tia lly, re sid e n ts and tra n s ie n ts d is trib u te d th e ir a c tiv ity d if f e r e n tly during the period p r io r to the re le a se of the w easels. The lo c a tio n of a mouse a t the p rec ise time the weasel was released provides some in sig h t in to where mouse a c tiv ity was centered, I have c h arac terize d the lo ca tio n of each mouse at the time the weasels were rele ased in two ways. Each mouse was p o sitio n ed "on the ground" or "above the ground" and "in the h a lf of the arena n e arer the mouse In je c to r" or "in the h a lf of the arena fa rth e r from the in je c to r". The co m e r braces in each arena were considered to be p a rt of the "ground", since each brace is continuous w ith the base of the frame. R esidents centered th e ir a c tiv itie s along a e r ia l runways in both halves of each arena. When the weasels were re le a s e d, th re e - q u a rte rs (76 percent) of the re sid e n t mice were lo cated above the ground and n early equal proportions were p o sitio n ed in each h a lf of the arenas. Fifty-tw o percent of the re sid e n ts were in the h a lf of the arenas fa rth e r from the In je c to r. Two resid en t mice, both m ales, e n tered t h e ir n e st box before the w easels were released. One of these mice was s t i l l in the n e st box when I released the w easel. T ran sien ts concentrated th e ir a c t iv i t ie s on the flo o r of each arena d ir e c tly in fro n t of the mouse in je c to r s. When the weasels were re le a se d, 77 percent of the tra n s ie n ts were on the ground and 73 p ercent were in the h a lf of the arena n earer the mouse in je c to r. No tra n s ie n ts entered the n est boxes p rio r to the weasels* re le a se.

45 30 The p o sitio n a mouse occupied a t the time the w easels were rele ased did not a ffe c t i t s lo c a ta b ility. Search times fo r r e s i dents and search tim es fo r tra n s ie n ts are not s ig n ific a n tly d if f e r ent fo r mice th a t were "on the ground" and those th a t were "above the ground" (each, p >.1 0, Mann-Whitney U T est). There is no s ig n ific a n t d ifferen ce between the search times fo r mice th a t were "in the h a lf of the arena n e arer the mouse in je c to r" and those th a t were "in the h a lf of the arena fa rth e r from the in je c to r" in e ith e r t e s t group (each, p >.1 0, Mann-Whitney U T e st). The lo c a tio n of a mouse when the w easels were released did not in flu en ce i t s o v e ra ll v u ln e ra b ility to capture. W ithin re sid e n t and tra n s ie n t groups, re s p e c tiv e ly, th ere are no s ig n ific a n t d if f e r ences in the t o t a l tim es to cap tu re, chase tim es, or numbers of escapes of mice th a t were "on the ground" and those th a t were "above the ground" ( a l l, p >.1 0, Mann-Whitney U T est). There was no p e rc e p tib le d ifferen c e in the amount of re sid e n t and tra n s ie n t a c tiv ity during the period p r io r to the weasels* re le a se. Behavior w hile the Weasels Searched the Arenas Most re sid e n ts and tra n s ie n ts a lte re d th e ir behavior p a tte rn s when the weasels began p a tro llin g the arenas. However, one re sid e n t (excluding the male th a t was in the n e st box when the weasel was re leased) and seven tra n s ie n ts continued th e ir a c t iv i t ie s w ithout re gard to the w easels. Some of these mice rev ised th e ir behavior before the w easels discovered them and began to give chase. The others were lo cated quickly. A ll mice (re sid e n ts and tra n s ie n ts ) th a t m odified th e ir behavior

46 31 a f t e r the w e asel's re le a se behaved sim ila rly. Mice from both te s t groups e ith e r assumed an elongate posture and crep t toward a more elev ated p o sitio n or froze. T ransients assumed an elongate posture and crep t to a hig her p o sitio n more frequently than re s id e n ts. R esidents froze more o ften than tra n s ie n ts. Among the re sid e n t and tra n s ie n t mice th a t a lte re d th e ir behaviors a f te r the weasels were re le a se d, 73 percent of the resid e n ts fro ze, whereas, 47 percent of the tra n s ie n ts fro ze. The r e s t of the re sid e n ts (27 percent) and tra n s ie n ts (53 percent) assumed an elongate posture and crep t to a hig h er p o in t. R esidents held th e ir freeze postures much longer than tra n s ie n ts. C h a ra c te ris tic a lly, re sid e n ts remained frozen u n til the w easels discovered them. A sin g le re sid e n t mouse abandoned i t s freeze p o stu re befo re the w easel was aware of i t s lo c a tio n. By comparison, 86 percent of the tra n s ie n t mice th a t froze moved before the w easels lo cated them. There is no c o rre la tio n between the way a mouse behaved and the p o sitio n i t had occupied when the w easels were released in e ith e r t e s t group. Freezing and creeping to a higher lo c a tio n in an elongate p o stu re appear to be equally adaptive. W ithin re sid e n t and tra n s ie n t groups, re s p e c tiv e ly, th ere are no s ig n ific a n t d ifferen c e s in the t o t a l times to cap tu re, search tim es, chase tim es, or numbers of escapes of mice th a t froze and those th a t assumed an elongate p osture and crep t to a h ig h er p o sitio n ( a l l, p >.1 0, Mann-Whitney U T e st).