Importance of Tactile and Visual Stimuli of Eggs and Nest for Termination of Egg Laying of Red Junglefowl

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 numberof eggsin the of clutch size. 483 484 THEOMEIJER [Auk, Vol. 112

TABLE1. Summaryof the main resultsfor four experiments:(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 bottom 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 sightof 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 increase 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 accumulated(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. 2). bation"on their own beforethe empty nestbox The massesof the last eggs in a clutch were was removed. Also, in this situation, females markedly lower (Fig. 1A). After removalof the waited almosttwo weeks (11.2 _+4.5 days) be- nest box, females were forced to stop incuba- fore laying new eggs. tion, and startedto re-lay after a period of 13.4 Femalesreacted significantly differently in _+2.8 days. the four experimentswith respectto the period Experiment2: Tactileand visualstimulation of in which laying stopped(ANOVA, F•,5o= 7.80, firstegg only.--When only the first egg laid was P < 0.001). Posthoctests (LSD test for unequal left in the nest box (all subsequentones were samplesizes; Sokal and Rohlf 1981)showed sig- removed),the hens reactedsimilarly to females nificantdifferences only betweenthe layingpe- in experiment 1. Incubation behavior devel- riod of femalesin experiment4 (eggsremoved opedslowly during the laying period.The birds every day) comparedto those of experiment 3 stopped laying after 8.4 _+ 3.1 days, clutches (eggsunder wire mesh; P = 0.02), experiment containedfour to eight eggs(n = 10; see Fig. 2 (first egg only left in nest; P = 0.005), and 2), and last eggswere again much smaller than experiment 1 (control; P < 0.001). The same the first ones. result was found for the number of eggslaid Eight of 10 femalesstarted to incubateduring per "clutch" (ANOVA, F3,so= 8.45, P < 0.001). the night (from two days before until two days after the lastegg was laid). They incubatedcon- DISCUSSION tinuously, on one egg only, until the nest box was removed. Of the other two females, one Terminationof egglaying.--When eggswere (no. 13) incubatedfor longer and longer periods allowed to accumulateinside the nest (experi- 486 THEOMEIJER [Auk,Vol. 112

ment 1), the time spent on the nest increased to the nest after they had left it in the late af- rapidly; Red Junglefowl hens laid relatively ternoon during the nest check.When only the small clutchesof five to seveneggs (see also first egg remained in the nest (experiment 2), Meijer and Siemers1994). This finding indicates one hen stoppedincubation after being driven that, directly or indirectly (Haftorn 1985), the off twice. This happenedalso once in experi- increase in incubation behavior turns off follic- ment 3 (eggsunder wire mesh). Of the 14 fe- ular development in the ovary in 6 to 11 days. maleswhose eggswere continouslyremoved It hasbeen arguedthat tactile stimulationof the (experiment 4), 5 stopped incubation after be- brood patchfrom the accumulatingeggs in the ing driven off only once.When the incubating nest leads to an increase in incubation behavior female could only seethe eggs(experiment 3), (Klomp 1970, Murton and Westwood 1977). In 4 of 10females stopped incubation on their own. bantamsthe onsetof incubationis initiated by When they couldneither touch nor seethe eggs an increasein the secretionof prolactin, which (experiment4), all 7 incubatingfemales left the also suppressesthe secretionof LH, leading to nest on their own. In experiments 1 and 2, all regressionof the reproductivesystem (Sharp femaleswere forced to stop incubation when I 1980, Lea et al. 1981, 1982, but see Sharp et al. removedthe nestbox. Theseexperimental find- 1988). ings indicate that to maintain incubation be- Experiment2, in which femaleskept only the havior visual stimuli of eggsare sufficientfor first egg in the nestand all following oneswere one-half of the hens. Incubation continued in removed after being laid, demonstratesthat all femalesreceiving tactile stimuli of the whole without accumulatingeggs in the nestthe tran- clutch. Tactile stimuli of only one egg in the sition from laying to incubationoccurred in a nest had the same effect. similar way. Even in a situation in which the Doesthe hen "count"the numberof eggsin a female returned to the nest and saw but could clutch?--To answer this question, Steen and not touch the (increasingnumber of) eggsbe- Parker(1981) conducted experiments (my con- side it (experiment 3), incubation behavior still trol experiment 1, and experiment 3 with the progressivelydeveloped and the ovary was wire mesh) and suggestedthat bantam "hens turned off in a period of 6 to 14 days. Most observethe actual number of eggsby eye and surprisingly,when eggswere removed contin- used these observations to decide when the uously(experiment 4), the laying femalesat also clutchhad reachedthe desiredsize and possibly on the nest longer and longer eachday. Within also to stimulatethe onset of brooding."The 6 to 29 days (œ= 14 days), all females stopped outcomeof experiment 2 (in which only the laying. Not only did female Red Junglefowl first egg laid stayedin nest box, and females stop laying, but the increasein incubation be- laid normal number of eggs)does not support havior, the overnight sitting (in an empty nest), Steen and Parker's ideas. the smaller size of the last eggs,and the two- Earlier, Moss and Watson (1982), in a reply week pausebefore new eggswere laid strongly to Steen and Parker (1981), showed that wild indicate that in this treatment females laid Red Grouse(Lagopus lagopus scoticus) lay clutch- clutchesof nine eggs. es of similar size whether or not someeggs are The differences in the time needed to turn removed from their nests. I think that this is off the ovary recorded in the four treatments the case for all determinate-laying species. were small (on average8 to 14 days).The big- However, Moss and Watson (1982) mentioned gest differenceswere in: (a) the period after further that captive Red Grouse, all of whose which the hens remained in the nest box over- eggswere continuallyremoved from the cage, night; (b) the degreeof disturbanceby the af- laid many more eggsthan the number in the ternoon inspection;and (c) the intensity of in- usual clutch (i.e. in captivity they behave as cubationat the end of the laying period. In the indeterminatelayers). The evaluationof deter- control situation(experiment 1), femalesstarted minate versusindeterminate laying needsto be to incubateduring the night on the day the last addressedusing standardmethods of egg re- egg was laid and often one day earlier. In the moval and addition (see Kennedy 1991). The other experiments,night incubation sometimes stagein the breeding seasonand in the laying startedone or even two daysafter the last egg period of one clutchwhen experimentsare con- waslaid. When all the eggswere left in the nest ducted can be critical. EuropeanKestrels (Falco (experiment1), all incubatingfemales returned tinnunculus),for example,are indeterminatelay- April 1995] Terminationof EggLaying 487

ovary (by about four days),resulting in smaller clutches (ca. two eggs fewer). When eggs ac- cumulate inside the nest (experiment 1) and the layingfemale gets additional tactile stimuli from the eggs,there is a further (insignificantstatis- tically) advancementof two days,and clutches becomeagain another egg smaller. The tactile stimuli of one egg (and briefly of two eggs,for the time betweenlaying an egg and leaving the nest subsequently;experiment 2) already are sufficientfor a suppressionof follicular development within eight days,a period for laying 7eqqs (tO days ) • clutchesof six eggs. clutchofSe•js(Bda¾s)geaas ½t/*dpys) !J e I Surprisingly, Red Junglefowl held in small groups of three to six females and one male Fig. 3. Summaryof developmentof incubation continued laying over more than two months behavior,termination of laying,and numberof eggs (laying 45-50 eggs,without longer pauses;un- laid by Red Junglefowlheld in pairs(one male and publ. data for 1992). Depending on the social one female)under four experimentalconditions. Bro- situation under which the chickens were held, ken line representsestimation of incubationbehavior incubation behavior develops almost sponta- of hens living in mixed groups(data not given). neouslyand laying stopswithin two weeks(one male and one female), or incubation development is suppressedand laying continuesfor months(harem situation; see dashed line in Fig. ers early in the season,but determinatelater on 3). Also, in individually housedturkeys whose (Beukeboom et al. 1988). European Starlings eggswere removeddaily, the time spenton the (Stumusvulgaris) switch from being indetermi- nestprogressively increased and laying stopped. nate to determinatelayers between the first and The turkeysincubated in an empty nest.In con- secondegg of a clutchof four to five eggs(Mei- trast,hen turkeyswith denervatedbrood patch- jet 1993).Another complication is that,as in the es visited nests the same number of times, but Red Junglefowl (experiment4 versus2), a num- occupiedthe nest for a shorter time, showedno ber of bird speciesreact differently to experi- increasein nest occupancy,and none showed mentsin which all eggsor all but the first are full incubation (Book et al. 1991). Stimulation removed(e.g. Blue Tits [Paruscaeruleus]; Fox in of the brood patch by the nest alone probably Haywood 1993,see also Kennedy 1991). increasesincubation behavior, and ultimately Visualand tactilestirnulL--Figure 3 illustrates leadsto terminationof egg laying. the importance of the tactile and visual infor- The resultsof experiments1 to 4 indicate that mation for the development of incubation be- Red Junglefowl, in a situation in which eggs havior, termination of laying, and clutch size are removedcontinually, stop laying within two in the RedJunglefowl hen. When all eggswere weeks after laying a "clutch" of nine eggs.The continually removed (experiment 4), nest oc- tactile stimuli of the nest alone can induce full cupancyslowly increasedto 3 to 4 h per day expressionof incubation behavior and termi- and, after occupyingthe nest overnight, fe- nation of laying. When the hen can see,or see malesstopped laying on averagewithin 14days. and touch, the increasingnumber of eggs,lay- In this situation, the hen returns to an empty ing stopsfour to six days earlier, respectively. nest,sits down, laysan egg,and leavesthe nest When only the first egg staysin the nest,laying and egg after a while. When the tactile infor- is also terminated six days earlier. Thus, it is mation is exactlythe same(i.e. only for brief clear that visual stimuli alone accelerate the de- periodbetween laying of eggand leavingnest), velopment of incubationbehavior and the ter- but the hen seesthe increasingnumber of eggs mination of laying; therefore, they are impor- next to the nest (experiment 3), there is an ac- tant in determination of clutch size. However, celeration in the development of incubation be- Red Junglefowldo not judge clutch size based havior and a significantadvancement in the on the visual observationof egg number, and suppressionof follicular developmentin the the sameis probably true for bantams. 488 THEOMEIJER [Auk, Vol. 112

ACKNOWLEDGMENTS nate egg-laying patterns:A review. Condor 93: 106-124. I am grateful to H. W. Prehn and U. Nienhaber for KLOMP, H. 1970. The determination of clutch size assistancein collecting the data, and to L. C. Holl- in birds: A review. Ardea 58:1-125. comb, G. D. Schnell, J. B. Steen, F. Trillmich, and two KRUIJT,J.P. 1964. Ontogenyof socialbehaviour in anonymousreferees for improvement of earlier drafts BurmeseRed Junglefowl (Gallusgallus spadiceus) of the manuscript. Bonnaterra.Behaviour Suppl. 12. LEA,R. W., A. S. M. DODS,P. J. SHARP,AND A. CHAD- LITERATURE CITED WICK. 1981. The possiblerole of prolactinin the regulationof nestingbehaviour and the secretion AFTON,A.D. 1980. Factors affecting incubation of luteinizing hormonein bloody bantams.J. En- rhythms of Northern Shovelers.Condor 82:132- docrinol. 91:89-97. 137. LEA, R. W., P. J. SHARP, AND A. CHADWICK. 1982. BEUKEBOOM,L., C. DIJKSTRA,S. DAAN, AND T. MEIJER. Daily variationsin the concentrationsof plasma 1988. Seasonalityof clutchsize determination in prolactin in broody bantams.Gen. Comp. En- the Kestrel, Falco tinnunculus:An experimental docrinol. 48:275-284. study.Omis Scand.19:41-48. MEIJER,T. 1990. Incubationdevelopment and clutch BOOK,C. M., J. R. MILLAM, M. J. GUINAN, AND R. L. size in the starling. Ornis Scand.21:163-168. KITCHELL. 1991. Brood patch innervation and MEIJER,T. 1993. Is the starlingStumus vulgaris a de- its role in the onset of incubation in the turkey terminate layer?Ibis 135:315-319. hen. Physiol. Behav. 50:281-285. MEIJER,T., S.DAAN, AND M. HALL. 1990. Familyplan- CALDWELL,P. J., AND G. W. CORNWELL. 1975. Incu- ning in the Kestrel Falcotinnunculus: The proxi- bation behaviorand temperaturesof the Mallard mate control of covariationof laying date and duck. Auk 92:706-731. clutch size. Behaviour 121:117-136. DRENT,R.H. 1975. Incubation.Pages 333-420 in Avi- MEIJER,T., AND I. SIEMERS. 1994. Incubation devel- an biology, vol. 5 (D. S. Farner, J. R. King, and opment and asynchronoushatching in jungle- K. C. Parkes, Eds.). Academic Press,New York. fowl. Behaviour 127:309-322. HAFTORN,S. 1981. Incubationduring the egg-laying Moss, R., AND A. WATSON. 1982. Determination of period in relation to clutchsize and other aspects clutchsize in Red Grousewithout implying the of reproductionin the Great Tit (Parusmajor). egg-'numerostat.'A reply to Steen and Parker. Ornis Scand. 12:169-185. Ornis Scand. 13:249-250. HAFTORN, S. 1985. Recent research on titmice in MURTON, R. K., AND N.J. WESTWOOD. 1977. Avian Norway. Pages137-155 in ProceedingsXIIX In- breedingcycles. Clarendon Press, Oxford. ternational Ornithological Congress(V. D. Ilyi- PARSONS,J. 1972. Egg size, laying date and incu- chev and V. M. Gravrilov, Eds.). Moskow, 1982. bation period in the Herring Gull. Ibis 114:536- Nauka Publishers, Moscow. 541. HALL,M. R. 1987. Externalstimuli affectingincu- SHARP,P.J. 1980. Femalereproduction. Pages 435- bation behavior and prolactin secretion in the 455 in Arian endocrinology(A. Eppleand M. H. duck(Anas plathyrhynchos). HoLm. Behav. 21:269- Stetson, Eds.). Academic Press, New York. 287. SHARP,P. J., M. C. MACNAMEE,R. J. STERLING,R. W. HALL,M.R. 1991. Endocrinologicaland behavioral LEA,AND H. C. PEDERSEN.1988. Relationships changesassociated with the onset of incubation betweenprolactin, LH and broodybehaviour in in the duck. Physiol. Behav.50:311-316. bantam hens. J. Endocrinol. 118:279-286. HALL, M. R., AND A. R. GOLDSMITH. 1983. Factors SHARP,P.J. 1993. Photoperiodiccontrol of repro- affectingprolactin secretion during breeding and duction in the domestic hen. Poult. Sci. 72:897- incubationin the domesticduck. Gen. Comp. En- 905. docrinol. 49:270-276. SOKAL,R. R., ANDF. J. ROHLF.1981. Biometry,2nd HAYWOOD, S. 1993. Role of extrinsic factors in the ed. W. H. Freeman and Co., San Francisco. control of clutch size in the Blue Tit Parus car- STEEN,J. B., ANDH. PARKER.1981. The egg-"nume- ruleus. Ibis 135:79-84. Lostat."A new conceptin the regulationof clutch- HAYWOOD,S. 1993. Sensoryand hormonalcontrol size. Ornis Scand. 12:109-110. of clutch size in birds. Q. Rev. of Biol. 68:33-60. ZEBRA,E., AND L. MORTON.1983. The rhythm of KENNAMER,R. A., W. HARVEY, AND G. R. HEPp. 1990. incubationfrom egg-layingto hatchingin moun- Embryonic development and nest-attentiveness tain White-crownedSparrows. Ornis Scand.14: of Wood Ducksduring egg-laying.Condor 92: 188-197. 587-592. KENNEDY, E. D. 1991. Determinate and indetermi-