FEEDING OF NESTLING AND FLEDGLING ELMER L. MOREHOUSE AND RICHARD BREWER

Transcription

1 FEEDING OF NESTLING AND FLEDGLING EASTERN KINGBIRDS ELMER L. MOREHOUSE AND RICHARD BREWER INFORMATION n the feeding f yung birds in the nest is available in varying quantity and utility fr many species. The feeding f fledglings has equally imprtant cnsequences t the ppulatin and the ecsystem, but infrmatin is distressingly meager. In a study f the breeding bilgy f the Eastern Kingbird, Tyrannu3 tyran u3 (L.), it prved pssible t btain bservatins n the feeding f yung birds during bth nestling and fledgling perids. PROCEDURE At nests data were gathered by direct bservatin thrugh telescpes giving magnificatins f 20-50X. The bserver usually sat n the grund in the pen. The nesting pairs shwed awareness f the bserver when he std, as when arriving r leaving, but nt when he was seated. Distinguishing male and female psed a prblem; behaviral differences usually allwed separatin f the sexes, but wherever pssible we als used individual differences in appearance. Fr yung ut f the nest, the prcedures fllwed were these: A family grup was lcated and bservatins begun if the bserver's presence did nt seem t disturb the birds. Observatins were c.ntinued as lng as any yung bird culd be seen. When bservatins were n lnger pssible, the bserver mved carefully t bring the brd r part f it back int range. Kingbirds are a favrable species fr such study, but even s the bservatin time as given in Table 2 represents nly abut half the time spent trying t make bservatins in the vicinity f a brd. Dati.ng f events in the fllwing discussin is in relatin t the hatching f the last egg during the nestling perid (thus, H-l day f hatching f the last egg, Hq-1 = the next day, etc.) and i.n relatin t the day the last yung left the nest during the fledgling perid (thus, Fq-0: day the last yung left the nest, F-]-I the next day, etc.). Ten nests f kingbirds were lcated during in Kalamaz Cunty, Michigan at the 40-acre Clny Farm Tract within the city limits f Kalamaz and the 500-acre Frt Custer Eclgical Research Area suth f the Kalamaz River near the village f Augusta. Fur nests were discvered during nest building, three during incubatin, and three after eggs had hatched. One yung bird was hand reared frm the day it left the nest (20 July) until it was returned t the area frm which it had been remved (2 August). The bird was kept utdrs (taken inside at night thrugh 25 July) at a dwelling in a suburban neighbrhd. BREEDING BIOLOGY Kingbirds arrive in the vicinity f Kalamaz abut the first week in May. They take up residence in pen areas with scattered trees and shrubs. The female builds the nest and lays a clutch f 2-4 eggs. Prbably mst pairs have begun egg laying by early June. Only the female incubates; the male usually perches near the nest during the female's inat- 44 The Auk, 85: January 1968

2 1968 Jan. ] MOREHOUSE AND BREWER, Feeding! Yung Kingbirds 45 TABLE 1 HOURLY RATE OF FEEDING AND PERCENTAGE OF FEEDINGS BY ¾ ALE AT SIX NESTS OF THE EASTERN KINGBIRD Day (H+) Hurs Feedings/nesting/hur Percentage bserved All Brds Brds! ]eedings nests! tw! three by male Feedings by birds f unknwn sex ignred. Sample f less than tw hurs. Brd f fur. One yung bird , ( 5.4 a ) , (12.9 TM ) (4.62's) (8.34) (4.84) --? tenfive perids. The incubatin perid is days; hatching usually ccurs in the space f a few hurs in the mrning. The time frm hatching f the last egg until all yung have left the nest is days. Mst birds have left fr the suth by the first week f September. DIET Adult insects were the main items fed t nestlings and fledglings, just as they are the main item f the diet f adults (Beal, 1897). Dragn- and damselflies (Odnata), grasshppers (Orthptera), flies (Diptera), and butterflies and mths (Lepidptera) were particularly imprtant. Items prbably secured by means ther than flycatching were ccasinally seen; f these, ]epidpteran larvae were the mst imprtant. Fruits made up a minr prtin f the diet at mst nests, but mulberries, Mrus rubra, were fairly imprtant at ne nest. Other fruits nted were cherries, Prunus sp., and dewberries and raspberries, Rubus spp. Occasinally tw fruits were brught t a nest at nce; animal items were always brught singly. Fledglings beginning t frage fr themselves ften ate fruit and als ften picked invertebrates frm leaves and branches; these items are prbably mre imprtant in the diet f birds at this age than at any ther.

3 46 MOREItOUSE AND BREWER, Feeding f Yung Kingbirds [ Vl. Auk n- 2O O n- 1.5 L9 10 ".51 0,I AM PM Figure 1. Hurly trend in feeding rate at Eastern Kingbird nest 3, based n 23 hurs bservatin n days Hnu9-12 (5-8 July 1963). Temperature range, 17-36øC; median f' hurly temperatures, Awakening time f the female was abut 5 AM; rsting time abut 8:30 PM. FEEDING OF NESTLINGS On the day f hatching, the feeding rate was very lw, ne feeding r less per yung bird per hur (Table 1). The rate then rse abruptly, crrespnding t an increase in feedings by the male. Thrugh the rest f the first half f nestling life the feeding rate remained fairly cnstant at abut three feedings per nestling per hur. Then a rise in the feeding rate crrespnded with an abrupt decline in brding by the female and an increase in the fractin f her feedings. Past this pint, the pattern fr twnestling nests and three-nestling nests diverged. At nests with tw yung, the rate increased irregularly thrugh the rest f nestling life. At nests with three yung, the feeding rate peaked abut H+9-11 at a level well abve that fr tw-nestling brds. Fr the last few days f nestling life, rates were again cmparable. In what appears t be the nly ther quantitative study f feeding rate,

4 1968 Jan. ] MOREHO,IJSE AND BREWER, Feeding f Yung Kingbirds T C9 Z 21_ 4, 5-0. I I I I I I 6 8 I AM igu e 2. uhy t end in feeding rate t E stem i.ngbkd est 4, b sed 19 u s bse v ti n d ys 2 ( 4-6 June 1964; temperature me n [ u ly temperatures, 20) nd 21 uts bse wti 24 June 1964; temperature nge, - 2 C; median [ u ly temperatures, 25). sti g time [ d ys 2-4 s but 8 ; lt d ys 9-12 but 8:20. A a ening time s nt determined. PM Herrick (1902: 27) bserved 91 feedings frm 8:54 AM t 12:50 PM at a nest cntaining fur yung (tw f which he had intrduced a few days earlier frm anther nest) abut 10 days ld. Fr tw yung the same age, ver the same span f hurs, we bserved 44 feedings. The rate per yung bird is virtually identical. At a given nest n a given day, the feeding rate varied with time f day, but we fund n daily rhythm f feeding that culd be cnsidered characteristic f the species. Nest 3 (tw nestlings) shwed a striking trend in feeding activity fr days 9-12: a peak early in the mrning, a trugh in mid-afternn, and the day's highest rate in the hur r s befre rsting when fd was brught at the rate f 30 r mre items an hur (Figure 1). Smewhathe same trend existed fr ther days at the same nest, and the evening peak was nticeable at nest 1. At nest 4 (three nestlings; Figure 2) feeding rates during days 9-12 tended t be mre cnstant (pssibly excepting an apparent drp t zer arund nn; this pint is based n less than an hur's bservatin n a single day). Gd data fr nest 4 are als available fr H+2-4, and the pattern is reasnably similar t days 9-12 (Figure 2). Fr these days the feeding rate was nt dependent n tern-

5 48 MOREHOUSe. A ro BREW, Feeding f Yung Kingbirds [ Auk I. Vl. 85 perature, at least in the range frm 21-33øC (thermmeter 2 feet frm the grund and shaded by the bserver). Belw 21øC feeding rates appeared smewhat higher and abve 33øC, smewhat lwer, but these samples are small and highly variable. FEEDING RATES DURING DEPARTURE rrolv[ THE NEST A transitinal perid f varying length exists when btk nestlings and fledglings are being attended. We spent abut 15.5 hurs bserving at tw nests during this perid. The hurly feeding rate per nestling was 6.1; fr fledglings it was abut 2. Difficulties in bserving the fledglings make this figure subject t greater errr than that fr the nestlings; even if the true figure were twice the bserved rate (and it certainly was nt), it is still evident that the yung birds in the nest remain the center f attentin. T speculate n the evlutinary value f such behavir, this perid represents a particularly vulnerable time; shrtening it as much as pssible shuld be evlutinarily advantageus. Because the larger, mre vigrus yung usually leave the nest first, cncentratin f feeding n the nestlings tends t bring them up t the develpmental level f the fledglings. FEEDING OF FLEDGLINGS Feeding rate fr the first few days ut f the nest was abut the same as r slightly belw that f the last several days f nestling life. Apparently the peak feeding rate fr the entire pst-hatching perid cmes 8-16 days after the yung have left the nest (Table 2). On F+10 the fledglings f nest 4 were fed at the rate f 10.3 feedings per yung bird per hur ver an bservatin perid cvering mst f the frenn (Figure 3). This is a rate almst twice as high as was bserved fr any substantial length f time while these yung were in the nest. Abut three weeks pst-fledging, the feeding rate declined abruptly t ne feeding per fledgling per hur r less. The last feeding f yung by adults was bserved F+35. Distinguishing between male and female parents was usually impssible nce the yung were fledged, but it was ften evident that bth cntinued t participate in feeding. N bvius differences were nted between the fd items given t fledglings as cmpared t nestlings. ENERGY INTAKE Feeding rates, althugh f interest in themselves, may nt directly indicate energy intake f the yung. This was almst certainly true fr hurt-hur cmparisns f kingbirds. The surces f the discrepancy were very high and very lw rates. Very high rates were fr perids when feeding was cncentrate dse t the nest and mst fd items were small, readily available insects. Very lw rates tended t be perids in which

6 Jan ] MOREllOUSE AND BREWER, Feeding f Yung Kingbirds 49 TABLE 2 I-[OIJRLY RATE OF POSTFLEDGING FEEDING OF FIVE BROODS OE EASTERN KINGBIRDS Nest 42 Other nests Day Feedings/ Feedings/ (F-k) Hurs Feedings fledgling/ Hurs Feedings fledgling/ bserved bserved hur bserved bserved a hur (2) (4) (2) (3) (4) (3) (2) (2) (3) (2) (2) (2) (2) (4) (2) (3) (2) (3) (2) (2) (2) (2) (2) Perid when at least ne yung bird was under bservatin. Three yung birds until Fq-23, then tw. Figures in parentheses dente numbers f yung being fed. feedings, when they did ccur, were f large items f (judging frm dry weight) times the calric value f the small insects caught near the nest. We suspect that day-t-day changes in feeding rate, if based n several hurs f bservatin per day, prbably reflect changes in calric intake fairly well. Values fr later days might be underestimated if the average size f fd items changed, but we believe that this was nt an imprtant cnsideratin at the nests we studied. We btained an estimate f grss energy intake fr the hand-reared bird

7 50 MOREHO JSE ^ 0 BREWEa, Feeding / Yung Kingbirds [ Vl. Auk 85 O O ß ß ß ß 3 2Yg ß 0 0 too 0 0 S 10 Is S0 SS DAYS PAST HATCktlNG Figure 3. Feeding rate at Eastern Kingbird nest 4 frm hatching until feeding f yung by adults was n lnger bserved. Slid symbls represent feeding f nestlings; pen symbls, fledglings. One fledgli.ng disappeared abut day 24. The dates run frm 12 June t 6 August fr ne day. On F+6 we placed an insect as nearly identical as pssible t each ne eaten by the bird int a jar f refrigerated water. At the end f the day this material was ven-dried at 110øC. Between 7:00 AM and 7:30 PM (air temperatures apprximately 24-33øC) the bird ate insects, mstly grasshppers, with a dry weight f 5.05 g. Using the calric value f grasshppers given by Glley (1961) this is a grss energy intake f abut 27 Kcal. The exact weight f the bird is unknwn but it was prbably abut 35 g (see Nrris and Jhnstn, 1958: 116). The estimate is abut what ne wuld expect frm a bird f this size under "existence" cnditins (see Davis, 1955: Figure 1; West, 1960: Tables 2, 4, and 6). In fact, its energy demands must have been slightly abve existence because it was still grwing feathers and it tk abut 30 flights f feet and abut 40 flights f 2-6 feet n this day. DEVELOPMENT OF THE YOUNG Shrtly after hatching, the yung have dark red-brwn skin, whitish dwn, and a yellw beak with a yellw-range gape. They lie quietly but rear up and gape when the parent arrives and als with n evident stimulus. By H+4 the skin appears blackish and a peeping call has becme evident. By H+6 pinfeathers are evident; by H+7 a dark tip is beginning n the bill. By H+10 the yung are kingbird-like in appearance and have heavy

8 Jan ] MOREIIOUSE AND BREWER, Feeding / Yung Kingbirds 51 pinfeathers. They are active, standing up, shaking and flapping their wings. Abut H+11 the peeping nte given previusly changes t a deek resembling the adult's ften used psitin nte. Leaving the nest and fledging can prbably be thught f as simultaneus fr kingbirds, althugh nt until abut F+2 are the yung able t fly lng enugh t gain altitude. Even then if they fly int extensive pen spaces, they tend t finish n the grund. One yung bird, six hurs after it left the nest and withut fd in the meantime, weighed g. This was the last bird t leave the nest and was the hand-reared bird already referred t. The tail feathers at this time were abut 30 mm lng. By F+I 1-13 the yung began t resemble adults, althugh a number f difference still allwed easy separatin f adult and yung. By F+27 the main pint f distinctin was the tail, which was shrter and mre drping in the yung. Within a day r tw after leaving the nest, the begging psture changed. The fledglings leaned frward mre and did nt gape s widely as nestlings, but they gave nthing like the cruching, wing-shivering display f many passerine fledglings. Fr the first several days the yung tended t sit still fr cnsiderable perids; they did nt accmpany the parents n lng flights, but when the adults came near the yung flew tward them and begged. Abut F+4, a special begging call develped (we rendered it as see-see-see-deek!), nt given by yunger fledglings r nestlings. By F+10 the yung culd be said t fly well, and the family grup nw began t range ver cnsiderably wider areas. On F+I 1 we nted that the yung flew "n wing tips" like adults. By F+23 the yung culd keep up with the adults in rdinary flight, but even as late as F+30 the yung tended t lse speed and altitude in the zig-zagging, acrbatic flights that ne thinks f as typical f the species. By F+7 yung birds in the field were bserved hpping arund in trees and flying ut frm them, chasing insects. They were nt bserved t catch any until the fllwing day. By F+7 the hand-reared bird had begun t treat live insects as adults d; it shk them and kncked them against its perch. By F+9 it tssed them int the air t arrange them headfirst. Manipulatin with the tngue was prminent. In the labratry a decrease in the amunt f fd taken at ne feeding and an increase in frequency f desired feedings was nted abut F+8. On F bth the hand-reared bird and wild birds were seen fraging n fruits. By F+10 yung in the field were extremely active in btaining fd frm the parents, ging s far as t fly ut and take fd frm the parent's beak in mid-air. By F+13 the yung's effrts t frage fr themselves were prminent. By F+26 the individual members f the family grup were ften seen hunting independently, but the yung still tended t fly t the parents whenever

9 52 MOREEIOUSE Ai D BREWER, Feeding / Yung Kingbirds [ Auk L Vl. 85 the adults caught smething. Th'e begging call was still given n F+35. On F+37 and thereafter n begging calls were heard, althugh the yung still chased adults with fd. Family grups were still intact when ur systematic bservatins ended in late August. TIMING O1. MOLT The mlt f birds is a tangled thicket int which we venture briefly t make a pint f purpsely limited scpe. Eastern Kingbirds, like mst members f the Tyrannidae breeding in temperate America, underg their fall mlt after suthward migratin (Dwight, 1900: : see als Jhnsn, 1963). This pattern, unusual fr passerines and migratry birds in general, ccurs als in swallws (Dwight, 1900: ). Jhnsn (1963: 882) pinted ut that bth families are "aerial-insect predatrs," but the crrelatin between this mde f fraging and the delayed mlt extends beynd these families. The Merpidae shw the delayed mlt (Van Tyne and Berger, 1959: 92), and s als d such aerial fragers as Caprimulgus eurpaeus, Apus apus, and Muscicapa striata (Stresemann and Stresemann, 1966: 36). Fr the Eastern Kingbird we ffer the fllwing hypthesis t accunt fr its delayed mlt. T begin with, we take it as a cmmnplace that mlt ccurs when energy is available fr it, rdinarily at a time cmplementary t the ther prime energy-requiring activities f the annual cycle such as feeding yung, migratin, and survival f lw temperatures (Pitelka, 1958; Kendeigh, 1949: 125). We believe that aerial fraging is a difficult way t make a living cmpared with many mdes f fraging. The appearance f effrt when even such skilled fliers as Cedar Waxwings, Bmbycilla cedrrum, indulge in flycatching suggests this. Further, we believe that attainment f full ability in aerial fraging is an extended prcess f maturatin r practice r bth. During mst f the apprximately 40 days we bserved yung ut f the nest, their flying ability increased. The perid f dependence is lng in kingbirds. The ttal perid frm first egg laid t last bserved feeding f fledged yung is abut 70 days. Fr an average pair in suthern Michigan this means that the yung are fed until near the middle f August. We suggest that the energetic demands f caring fr the yung d nt permit mlt befre this time. Suthward migratin befre cld weather and the decline f flying insects is a necessity (fr a graphic accunt f what may befall kingbirds and ther aerial fragers when fd supplies and temperatures are lw, see Andersn, 1965). Over much f the breeding range f the kingbird, the intervening perid wuld allw nly a very rapid mlt. Fr birds s whlly dependent n aerial fraging, a rapid mlt migh't nt be energetically feasible if it impaired their flying ability (Jhnsn, 1963: 882).

10 Jan ] MOREllOIJSE AND BREWER, Feeding / Yung Kingbirds 53 We regard many pints f this hypthesis as applicable t ther flycatchers and aerial fragers in ther families. In sme cases, the lng perid f dependency (and maturatin) may be spent in the nest (e.g., swallws and Apus apus); in thers, it may be as in the kingbird, but bservatins during pst-fledging phases f the life cycle are very scant. Accrding t Fry (1967), yung f the White-thrated Bee-eater, Merps albicllis, (which mlts n its dry seasn "wintering grunds" fllwing migratin) are dependent fr a prtracted perid f 6-8 weeks after fledging. (At this pint, we are left with a number f aerial fragers that d nt mlt befre migratin, including sme tyrannids, and als several species that are nt aerial fragers but that mlt after migratin. At the risk f verextending urselves, we will pint ut that the latter grup reads in part like a list f characteristic nnpasserine species f tundra and nrthern taiga [see Stresemann and Stresemann, 1966: 36]. Fr these species, the advantage f pstmigratry mlt may lie in the necessity fr leaving the breeding grunds sn after the yung are reared, even thugh th'e yung d nt require extended care. Fr the rest in bth categries, we fall back n the pint that has been ften made and that is bviusly true: Timing f mlt is a character that is highly susceptible t selectin n the specific level. Species that are able t raise ne brd and als mlt befre migratin d s; species that are able t raise tw brds and als mlt d s; species that are able t raise ne brd and als either mlt r care fr a secnd brd d ne r the ther; etc.). ACKNOWLEDG1V ENTS Part f this paper is based n a thesis presented by Mrehuse in partial fulfillment f the requirements fr the degree f Master f Arts, Western Michigan University, Part f the wrk was supprted by a grant frm the Western Michigan University Faculty Research Fund t Brewer. The tract f land in the Frt Custer Military Reservatin n which a large part f the study was cnducted was made available t Western Michigan University by license frm the Department f the Army. Sme f the bservatins included here were made by Jack W. Kammeraad and Charltte Calhun; we acknwledege with thanks their careful, perceptive wrk. Cmments n the manuscript by Harld D. Mahan and Gerge C. West prved helpful in revisin. We are als greatly indebted t ur wives. SUI IV ARY The feeding f yung Eastern Kingbirds was studied in Kalamaz Cunty, Michigan, ; included were 141 hurs f bservatin during the nestling perid and 74 during the fledgling perid. Insect images were the main fd brught t nestlings and fledglings. Feeding rate increased ver the curse f nestling life, but the peak rate f feeding came 8-16 days after the yung were ut f the nest. A lng decline fllwed,

11 54 MOREHOUSE A BREWER, Feeding! Yung Kingbirds [ Auk [ Vl. 85 leading t apparent cessatin f feeding f yung by adults abut 35 days after fledging. During the perid when the yung are leaving the nest, feeding effrt is cncentrated n the nestlings. Feeding rate is prbably nt an accurate reflectin f energy supplied t the yung; fr kingbirds, fr day-t-day cmparisns, it may serve adequately. A hand-reared fledgling n the sixth' day ut f the nest cnsumed abut 5 g (dry weight) f insects, r abut 27 Kcal. Fledglings can frage by flycatching 8 days after leaving the nest; hwever, their flying ability increased ver mst f the apprximately 40 days pst-fledging that they were bserved. A hypthesis is put frward t explain the fact that the fall mlt f kingbirds ccurs after suthward migratin. It is suggested that the energetic demands f caring fr the yung ver an extended perid f time cmbined with the need t migrate suthward befre fd and weather cnditins becme unfavrable d nt allw an aerial frager a sufficient interval fr mlting. LITERATURE CITED A qderso q, D.W Spring mrtality in insectivrus birds. Ln, 117: 134. BEA ;, F. E. L Sme cmmn birds in their relatin t agriculture. U.S. Dept. Agric. Farmers' Bull. 54: DAVIS, E. A., JR Seasnal changes in the energy balance f the English Sparrw. Auk,?2: DWmHT, J., JR The sequence f plumages and mults f the passerine birds f New Yrk. Annals N.Y. Acad. Sci., 111: FRY, C.H Lipid levels i.n an intra-trpical migrant. Ibis, 109: GOLL ¾, F. B Energy values f eclgical materials. Eclgy, 41 : HEP. a C C, F.H The hme life f wild birds. Putnam's, New Yrk. 148 pp. JH qs q, N.K Cmparative mlt cycles in the tyrannid genus Empidnax. Prc. XIII Intern. Ornith. Cngr.: KENDEICH, S.C Effect f temperature and seasn n energy resurces f the English Sparrw. Auk, 66: NPm S, R. A., A qd D. W. JO tnsto q Weights and weight variatins in summer birds frm Gergia and Suth Carlina. Wilsn Bull., 70: P Tm; CA, F.A Timing f mlt in Steller Jays f the Queen Charltte Islands, British Clumbia. Cndr, 60: STR SE A q q, E., A qd V. STRESmVrA qn Die Mauser der ViSgel. J. fiir Ornith., 107 (special n.): viii -[- 445 pp. WEST, G.C Seasnal variatin in the energy balance f the Tree Sparrw in relatin t migratin. Auk, 77: VAn TYm, J., A D A. J. BERaER Fundamentals f rnithlgy. New Yrk, Wiley. C. C. Adams Center fr Eclgical Studies, Department f Bilgy, Western Michigan University, Kalamaz, Michigan (Present address f first authr, Highland Park Cmmunity Cllege, Highland Park, Michigan).