The Auk 112(2):483-488, 1995 IMPORTANCE OF TACTILE AND VISUAL STIMULI OF EGGS AND NEST FOR TERMINATION OF EGG LAYING OF RED JUNGLEFOWL THEO MEIJER Departmentof Ethology,University of BieIefeld,P.O. Box100131, 33501Bielefeld, Germany ABSTRACT.--Experimentswere conductedto separatethe influence of tactile and visual stimuli emanating from the nest or eggs on the development of incubation behavior, the terminationof egg laying, and the determinationof clutchsize. Red Junglefowl (Gallus gallus spadiceus)hens, whose eggswere left inside the nest (experiment 1), receivedboth tactile and visualinformation, remained in the nestbox longer,and stoppedlaying after eight days (or sixeggs). Sixteen or 17females incubated. Leaving only the firstegg in the nest(experiment 2) gavesimilar results. When the eggslaid were placedunder a wire-meshbasket (experiment 3) suchthat the hen couldsee but not touchthe accumulatingeggs, laying stopped two days (or one egg) later than in experiment1, and mosthens "incubated"on the empty nestuntil the nestbox wasremoved. Surprisingly, when eggswere continuallyremoved (experiment 4), hensalso incubated progressively more, stopped laying after two weeks(or nine eggs), and then sat on the empty nest for one or more days. Stimulation of the brood patch by the nest alone led to more incubationand to termination of egg laying. Visual stimuli alone providedby eggsaccelerated both processesand were sufficientfor one-half of the hens to maintainfull incubationbehavior. Red Junglefowl do not appearto judgeclutch size visually. Received9 December1993, accepted25 February1994. DURING THE BREEDINGSEASON, a female has to nest. The few experimentsby which tactile in- make two important "decisions":when to start formation coming from the brood patch was laying, and when to stop laying. The period manipulatedby localanesthesia (Hall and Gold- between the onset and the end of egg laying smith 1983) or denervation (Hall 1987) failed (as well as the interval between eggs) deter- to show a direct behavioraleffect in incubating mines the number of eggs in a clutch (clutch female domestic ducks (Anas plathyrhynchos). size). Denervation of the brood patch in laying tur- During the laying period, eggsaccumulate in keys (Meleagrisgallopavo; eggs removed contin- the nest, and females of both altricial (Haftorn ually) shortenedthe time spent in the nest and 1981, Zebra and Morton 1983, Beukeboom et al. inhibited full development of incubation be- 1988, Meijer 1990) and precocialspecies (Par- havior (Book et al. 1991). Experimentsto test sons 1972, Caldwell and Cornwell 1975, Drent the influence of tactile and visual stimuli sep- 1975, Afton 1980, Kennamer et al. 1990, Hall aratelyduring the laying period are even rarer. 1991,Meijer and Siemers1994) sit on the nest Steen and Parker (1981), conducting experi- for a longer time each day. At the end of the mentsin which eggsaccumulated under a wire- laying period, femalesincubate for almostthe mesh basket beside the real nest, claimed that whole day and, in the ovary, follicle develop- bantam (Gallusdomesticus) hens can judge their ment becomessuppressed. The gradualincrease clutch size by visual stimuli alone. of incubationis a goodpredictor of clutch size I present data on the egg-laying behavior of (Haftorn 1981, 1985, Meijer 1990, 1993, Meijer Red Junglefowl (Gallusgallus spadiceus; Kruijt et al. 1990) 1964, Meijer and Siemers 1994). ! tried to sep- Visual and tactile stimuli can inform the lay- arate the influence of stimuli emanatingfrom ing femaleabout the numberof eggsin the nest the nest from thoseprovided by eggs.Also, I (Klomp 1970, Murton and Westwood 1977). It set up an experiment to distinguish the influ- is apparentfrom egg-removaland egg-addition ence of visual and tactile information on the experiments(for reviews, see Kennedy 1991, development of incubation behavior, the ter- Haywood 1994)that femalesof a variety of bird mination of egg laying, and the determination speciestake noticeof the number of eggsin the of clutch size. 483 484 THEOMEIJER [Auk, Vol. 112 TABLE1. Summaryof the main resultsfor four ex- periments:(1) eggs accumulated inside nest; (2) only firstegg laid left in nest;(3) eggsaccumulated next to nest under wire mesh; and (4) eggs removed every day. No. hens Day when Ex- (%) on Clutch stopped peri- No. nestat size laying ment hens night (œ+ SD) (œ+ SD) 1 17 16 (94) 6.1 + 0.9 8.2 + 1.3 2 10 8 (80) 5.6 _ 1.3 8.4 _+ 3.1 .E •" ©© - •©©© - © - © - 3 13 11 (85) 7.2 _+ 1.9 9.8 _+2.8 4 14 7 (50) 9.0 + 2.8 13.9 + 5.9 METHODS Experimentswere conducted using 21 pairs of Red Junglefowlhatched from eight clutches in the early summerof 1992(see Meijer and Siemers1994). The birdslived in largeoutdoor aviaries in threemixed groupsover the winter and started to layduring late 200 Decemberand January(see Sharp 1993) at an ageof 100 six months.Eggs were removeddaily. From25 Feb- ruary,they were held pairwise(one male and one female)in adjacentoutdoor aviaries (1.5 m wide x 4.5m long x 3.0m high)under natural daylight and days after first egg temperatureconditions. Each pen contained a shelter Fig. 1. Representativeexamples of egg-layingpat- (1.0 x 1.0 x 1.5m) with roostingperches and a nest terns (top of each diagram)and developmentof in- box(27 x 50 x 23 cm).Commercial chicken food and cubationbehavior when: (A) eggsaccumulated inside waterwere providedad libitum daily. nest(experiment 1); (B) eggs accumulated next to nest As a measure of incubation behavior (see fig. 1 in under wire mesh (experiment 3); and (C) eggs re- Meijer and Siemers1994), nest temperaturewas re- movedevery afternoon (experiment 4). Eggmass (g) cordedevery 5 min with NiCrNi thermistorssituated shownwithin eggsymbol; pause days indicated with on the bottom of the nest cup and connectedto a 16- dash. Full incubation, which lasted until nest box channeldatalogger (Squirrel 1205, Grant England). removed(indicated by arrow)is representedby solid To separatetactile from visualstimuli nest boxes were line. At end of laying, females38, 32, and 41 attended divided into two halves, one of which was covered emptynest only for one night (indicatedwith N). with wire mesh (seeSteen and Parker 1981). The bot- tom of the wooden nest box was covered with a rubber (after two to three weeks), one of the other three padhaving fingers (3.5 mm diameter,15 mm height) toppedwith a nipple(0.9 mm diameter,1.0 mm height; experimentswas carried out (the orderof which was randomized). Vencomatic,The Netherlands), over which was place a layerof hay.In the lateafternoon (1600-1700 MET), nestboxes were checked,eggs were marked,and eggs RESULTS weighedto the nearest0.01 g (SartoriusPt 120).Be- tween late March and early June, four experiments Experiment1: Full tactile and visual stimula- were conductedin which: (1) eggswere put back,so tion.--In the control situation, when females that eggsaccumulated inside the nest(n = 17different were allowed to keep their eggsinside the nest, females);(2) only the first egg laid wasput backand they stoppedlaying after an averageperiod of otherswere removed (n = 10); (3) eggswere put back 8.2 +_SD of 1.3days (n = 17;see Table 1). During into other half of nest box, under wire mesh, so that this period, femalesremained in the nest box accumulatingeggs were within sight of the hen, but for a longer period each day (seeFig. iA), and she could not touch them (n = 13); (4) eggs were incubatedalso during the night on the day the continuouslyremoved (n = 14). When femalesstopped laying, they were allowed penultimateor the lastegg was laid. Sixteenof to incubatefor a maximum of four to five days,after 17 females incubated continuously from the which the nest box (with eggs)was removed for a momentthe lastegg was laid. The other female periodof five days.When hensstarted to lay again (no. 30) attended the nest box 30 to 50 min while April 1995] Terminationof EggLaying 485 (from 20 to over 250 min); however,after being driven off the nest twice at the end of laying (during the afternoon inspection),she did not start full incubation. The other female (no. 9) stoppedlaying after five eggs,without any in- crease in incubation behavior. Experiment3: Permanentvisual stimulation of ß eggs.--Whenthe eggswere put under the wire mesh in the afternoon so that females could only seebut not touch them, the hensstopped laying after 9.8 _+2.8 days(range 6-14 days,7.2 _+1.9 eggs,n = 13;Fig. 2). All 13 femalesshowed an increasein incubationbehavior during the laying period (see Fig. lB), two did not start night incubation,five incubatedduring one (e.g. no. 38; seeFig. lB) or two nights,and the other six incubatednext to the clutch on an empty nest until the nest box was removed (e.g. no. 34; see Fig. lB). Experiment4: No visual.stimulation.--When I one egg acc. eggs acc. eggs eggs continually removed the eggslaid (in the late afternoon),hens stopped laying after 13.9 + 5.9 Fig.2. Numberof eggslaid by femaleswhen: only days (range 6-29 days,9.0 _+2.8 eggs,n = 14; first egg laid left in nest (experiment2); eggs accu- mulated(acc.) inside nest (experiment1); eggsaccu- see Fig. 2). Nest attendanceslowly increased, mulated next to nest under wire mesh (experiment and egg massdecreased as laying progressed 3); and eggsremoved every day (experiment4). Each (Fig. 1C). Five of 14 females did not return to dot representsclutch size of single hen. the empty nest after being gently driven off during the afternoon control (they had incu- batedthe last eggat that momentfor 198 + 107 laying eachof the first four eggs,and over 200 min). Another sevensat on the empty nest con- min for the last (eighth) egg, but did not in- tinuously at the end of the laying period for cubateduring the night. one to three days. All femalesstopped "incu- Clutchescontained 6.1 _+ 0.9 eggs (Fig.