mass decreases and body composition changes

REMEX GROWTH AND BODY MASS OF MALLARDS DURING WING MOLT MAREK PANEK AND PRZEMYSLAW MAJEWSKI Plish Hunting Assciatin, Research Statin, 62-055 Czempin, Pland ABSTRACT.--We captured, banded (n = 4,129), and weighed (n = 809) Mallards (Anas platyrhynchs) during wing mlt in western Pland. The cnditin f remex develpment was assessed (n = 3,421). We recaptured and remeasured 248 birds. The rate f remex grwth in males (calculated by tw methds) was 6.7 and 5.5 mm/day (P < 0.02). Males regained flight capability in 22-29 days, when remiges had reached 75-83% f final length. During the flightless perid, males and females lst 12% f bdy mass. Birds whse flightless perid was extended t replace nly a few damaged quills cntinued t decline in bdy mass, which indicates that rate f mass lss was unrelated t csts f feather synthesis. We cnclude that decrease f bdy mass is related t cnstraints n fraging time. We think this is a respnse t high expsure t predatin during fraging. Reductin f flightlessnesseems t be realized by a high grwth rate f remiges, which was almst cnstant and independent f bdy mass. Received 24 August 1988, accepted 25 September 1989. LIKE ther waterfwl, Mallards shed all their STUDY AREA AND METHODS primaries and secndarie simultaneusly, and are flightless during the perid f wing mlt. This study was cnducted in the fldplain f the Flightless birds are mre susceptible t preda- River Warta at its cnfluence with the Odra River, tin, and mvements are cnstrained. This sit- western Pland (Majewski 1986). Flightless ducks uatin influences habitat selectin, antipreda- cncentrate in willw bushes (Salix spp.) surrunded tt behavir, fraging, and energy budget. Bdy by shallw water. The number f male Mallards that mlt here reaches 25,000, many times greater than the mass decreases and bdy cmpsitin changes number f lcal breeders. during flightlessness. Several hyptheses at- In 1981-1982 flightless Mallards were surrunded tempt t accunt fr the changes in bdy mass. and driven int a net enclsure (Majewski 1981). Birds Hansn (1962) cncluded that remex mlt is a were banded (3,788 males and 341 females), weighed perid f great nutritinal stress fr Canada t the nearest 20 g (640 males and 169 females), and Geese, and birds must catablize bdy tissues the ninth primary was measured t the nearest 1.0 t build feathers. Ankney (1979) argued that mm (3,143 males and 278 females). The birds were flightless geese can meet their nutrient require- then released. We recaptured 337 males and 13 fements frm the diet, and that maintenance f males, typically after 3-9 days. Each was remeasured. a superfluus reserve wuld be a waste f en- Because mst females were trapped late in the seasn, ergy. Decreased bdy mass during mlt may be there were relatively few recaptures. We calculated the rate f remex grwth frm difadaptive, because it enabled birds t fly befre ferences between lengths f the remiges divided by cmpleting grwth f remiges, and this reduced number f days between capture and recapture f the flightless perid (Duthwaite 1976, Dean each individual (n = 237). Birds with brken r pulled and Skead 1979, Owen and Ogilvie 1979, Bailey remiges were excluded, but sme damage t remiges 1985, Austin and Fredricksn 1987, Sj6berg might have been verlked. When caught fr the 1988). Yung and Bag (1982) suggested that first time, sme birds shed their remiges, but reducks may lse feeding pprtunities as a result grwth was nt yet visible. Recapture f these birds f secretive behavir. Duthwaite (1976) sug- (n = 12) prvided remex grwth rates frm the begested that reserves accumulated befre the mlt ginning f feather replacement. The remex length required t resume flight was make birds less vulnerable t fd shrtages established frm the lngest primaries amng capwhere they wuld be expsed t predatrs. tured birds. We assumed that birds capable f flying These hyptheses are nt mutually exclusive, culd nt be captured. We measured final length f and Pehrssn (1987) suggested that limitatin the ninth primary in 18 males and 50 females caught f fraging and use f bdy reserves minimalize r sht in ther seasns. We estimated duratin f expsure t predatin and simultaneusly flightlessness frm the grwth rate f remiges. shrten flightlessness. Changes in bdy mass during mlt were calculated 255 The Auk 107: 255-259. April 1990

256 PANEK AND MAJEWSKI [Auk, Vl. 107 e/ n=12 r% Q951 p 0001 y= 6,7x-15...... b......... day after first c tching Fig. 1. Length f the ninth primary in recaptured, flightless male Mallards, trapped initially with n emerging primary feathers. using regressin f bdy mass t remex length. This value was assumed t represent a mlt-stage index. Only birds captured the first time were used. This methd excluded pssible influence f capture n bdy mass. We als measured change f bdy mass in 26 retrapped birds. Date f mlt initiatin in captured birds was estimated by backdating, using the average rate f remex grwth. RESULTS Curse f remex mlt.--remiges in males caught the first time with n emerging primaries grew 6.7 (SE = 0.5) mm per day (Fig. 1). In males captured twice with grwing remiges, the rate averaged 5.5 ram/day (n = 237, SD = 0.94, SE = 0.06, Fig. 2). Exceptinally lw values might have been caused by undetected damage t grwing remiges that inhibited their grwth. This may partly explain differences in remex grwth rates estimated by the tw methds (t = 2.475, P < 0.02). Average grwth rate f female primaries calculated frm remeasuring was als 5.5 ram/day (n = 11, SD = 0.56, SE = 0.17). Remex grwth rate in males decreased ver the flightless perid (Fig. 2). N males with ninth primary lnger than 150 mm were caught, and the number f males captured decreased markedly abve 135-ram primary length. Presumably mst males culd fly at this stage (135-150 ram) f remex length. This was 75-83% f the final length f 181 mm (n = 18, SD = 6, range: 172-193). The lngest ninth tength f 9th primary (mm) Fig. 2. Remex grwth rates f male Mallards at varius stages f primary grwth based n measurements f the ninth primary averaged fr tw captures (n = 237, y = 5.8 + 0.0018x - 0.000085x 2, R = = 0.0624, P < 0.001). primary in females was 123 min. Small samples f captured females (n = 278) did nt permit us t detect any gradual decrease f remex length. Apparently a majrity f females culd fly when the primary reached 125 mm (73% f final length f 171 mm In = 50, SD = 6, range: 157-185]). We estimated initial stage f mlt (time elapsed between nset f flightlessness and emergence f small bld quills) frm recapture f birds caught befre regrwing remiges were visible (n = 12). Time f quill appearance was calculated by backdating using average grwth rate f 5.5 ram/day. Regrwth began, n average, ne day after the first capture. This is nly part f the initial stage f mlting, because all captured birds were flightless already. Assuming that birds can be caught with equal prbability n any date between nset f flightlessness and the emergence f remiges, we estimated this initial stage f mlting lasted tw days. Based n estimated remex grwth rate f individuals caught the first time withut emerging feathers (6.7 ram/day), remex length abve which males can fly (135-150 ram) is reached in 20-22 days. We predicted 25-27 days f flightlessness frm the grwth rate in birds with twice-measured remiges. Assuming tw days frm the lss f flight ability t the appearance f bld quills, we calculated that male Mallards in this ppulatin were flightless fr 22-29 days. Changes in bdy mass.--bdy mass f mlting male Mallards ranged frm 870 t 1,420 g (g = 1,120 g, n = 640, SD = 90). Bdy mass f females

April 1990] Wing Mlt and Bdy Mass 257 36 134 173 131 86 38 15,., lo..c -2. -4 lent h f 9fh primary(rnm) Fig. 3. Bdy mass f male Mallards at varius stages f remex grwth. Means, +2 SE, +2 SD, and ranges are shwn; df = 6, r = -0.9697, r 2 = 0.9403, P < 0.001, y = 1170-0.997x. Sample sizes are given fr each perid. ranged frm 760 t 1,180 g (œ = 990 g, n = 169, SD = 85). Bdy mass f bth males and females declined during mlt (Figs. 3 and 4). Regressin equatins fr this trend indicate a 12% decrease in mass fr bth sexes during the mlting perid. Changes f bdy mass f males fund by weighing the same individuals recaptured after E 0. looo, 8 28 6 33 18 12 6 -s. ; «' + ' " (3 recapture intervet (deys) Fig. 5. Bdy mass changes in Mallard males captured twice (n = 26). 3-12 days varied frm +20 g t -250 g. The average decrease was 17 g/day (n = 26, SD = 12, Fig. 5), and was significantly greater than 5 g/day calculated fr birds captured nly nce (t = 4.895, P < 0.001, Figs. 3 and 4). Lss f bdy mass was nted until the ninth day after capture (Fig. 5). Average rate f decrease f bdy mass in individuals recaptured <300 m frm first capture was 13.7 g/day (n = 21) and was lwer than in individuals recaptured at 1,300-1,800 m (28.7 g/day, n = 5, t = 2.696, P < 0.05). Bdy mass changed rapidly amng sme individuals and thers maintained their mass (Fig. 5). Males that remlted individual damaged remiges were flightless lnger, and individuals recaptured in day 37-50 f flightlessness weighed 21% less than thse beginning t mlt (Fig. 6). N crrelatin was fund between bdy mass and remex grwth rate in males (Fig. 7), althugh bth values decreased during mlt. 8 [ength f 9fh primcry (mm) Fig. 4. Bdy mass f female Mallards at varius stages f remex grwth. Means, +2 SE, +2 SD, and ranges are shwn; df = 5, r = -0.8137, r = 0.6621, P < 0.05, y = 1020-1.01x. Sample sizes are given fr each perid. DISCUSSION Decreased bdy mass appears t be characteristic f dabbling ducks during mlt. In nine ther species r ppulatins, bdy mass de- creased by 10-24% during flightlessness (Shewell 1959, Rwan 1963, Flk et al 1966, Oring 1969, Duthwaite 1976, Dean and Skead 1979, DuBwy 1985, Pehrssn 1987, Sj6berg 1988; sme f the data recalculated). N significant decreases in bdy mass were reprted in tw

258 P., ' EK AND MAJEWSKI [Auk, Vl. 107 1400 27 15 11 nø1000 ß ß ß I ß E?,- 6,0- ß ß 6 1'0 0 ] ] 0 dy f fiight essness Fig. 6. Bdy mass f male Mallards during the nrmal perid f flightlessness (means and ranges fr the beginning and end f flightlessness), and masses f individuals remaining flightless lnger due t remlt f remiges damaged during capture. bdy mss {g) Fig. 7. Remex grwth rate and bdy mass in male Mallards. Bdy mass f individuals at first capture was cmpared with remex grwth rate between the first and secnd capture. cases (Yung and Bag 1982, DuBwy 1985), but samples were small. The csts f feather replacement prbably d nt cause nutritinal stress as suggested by Hansn (1962) and are nt the chief reasn fr the decrease in bdy mass in Mallards. We fund that individuals that remained flightless lnger because f damaged remiges cntinued t lse mass, althugh nly a few remiges were being replaced. The remex mlt is preceded by mlt f bdy plumage whse mass is 2.5 times that f the feathers replaced during the flightless perid (Yung and Bag 1981, 1982). Hwever, increased bdy mass befre the remex mlt ccurs in dabbling ducks (Flk et al. 1966, Oring We think that prlnged bdy-mass lss may be caused by an increase in secretive behavir after capture, and by the mve t new sites where fraging was less effective. The Ankney (1979) hypthesis (t explain decrease f bdy mass as lss f superfluus reserves) cannt be applied t ur case. We fund that individuals that remained flightless lnger cntinued t lse mass, and their mass was much lwer than ducks during nrmal mlt (Fig. 6). They did nt feed mre intensively t maintain bdy mass when they depleted reserves. In ur pinin, limited fraging and the use f bdy reserves during flightlessness are respnses t high predatin n dabbling ducks that frage 1969, Duthwaite 1976, Yung and Bag 1982, in shallw waters. Secretive behavir and shrt DuBwy 1985, Pehrssn 1987). This may be related t the use f resurces during flightlessness. The areas where dabbling ducks mlt appear t have abundant fd resurces (Gavrin frays ut f shelter minimize expsure t predatin. Greater predatin and limited mvements shuld prmte a shrter flightless perid. This 1970, Lebret 1971, Krtegaard 1974, SjtSberg is supprted by the bservatins that ducks be- 1988). By implicatin, the decrease f bdy mass is nt a result f limited fd supply. Pehrssn (1987) fund that captive Mallards fed ad libitum increased bdy mass befre remiges were shed and lst bdy mass during flightlessness, regardless f fd quality. We think that lss f bdy mass during wing mlt results nt frm high nutrient requirements r limited fd supplies, but frm cnstraints n fraging time. We fund increased lss f bdy mass after capture until at least the ninth day. This cannt be related t nly handling r mvements after release, althugh lss f bdy mass was higher in individuals that mved lnger distances. gin t fly befre cmpleting remiges grwth. Lw bdy mass may favr earlier flight. Pehrssn (1987) calculated that tw grups f Mallard males that differed in bdy mass n average 80 g started t fly within 0.5 day f each ther. This des nt supprt strngly the hypthesis that limited fraging during mlt is related t a decrease f bdy mass which wuld allw birds t fly sner. We believe that hiding during the day is a mre imprtant respnse t predatin than reductin f the flightless perid by lsing bdy mass. Owen and King (1979) fund a significant, psitive crrelatin between the early grwth

April 1990] Wing Mlt and Bdy Mass 259 rate f remiges and bdy mass f male Mallards during the wing mlt, but nt in female Mallards. We fund n such crrelatin fr males (Fig. 7). Remiges apparently grw independently f cncurrent reserves. Pehrssn (1987) fund n difference in remex grwth rati in Mallards fed n high and lw prtein fd. Lw prtein diet influenced remex grwth nly after the flightless perid and prduced shrter primaries. Fie als shwed that remex grwth rate decreased slightly during flightlessness, and that a distinct decrease began 30 days after the remiges were shed and when birds regained their flying capability. In ur pinin, flightlessness is shrtened by an apparently high grwth rate f remiges which is almst cnstant and independent f bdy mass. ACKNOWLEDGMENTS We are grateful t P. Beszterda, J. Engel, and P. Madry fr assistance in data cllectin, and F. Cke, J. Engel, G. S. Hchbaum, R. Mntgmery, Z. Pielwski, J. D. Reynldsß M. Richards, R. Rckwell, and A. Tamislet fr prviding cnstructive criticism n earlier drafts f this paper. We als thank D. Padley fr translating the manuscript. J. Swensn imprved the English. The study was supprted by Plish Ministry f Natinal Educatin--Prgram RR.II.17. LITERATURE CITED ANKNEY, C. D. 1979. Des the wing mult cause nutritinal stress in Lesser Snw Geese? Auk 94: 68-72. AUSTIN, J. E., & L. H. FREDRICKSON. 1987. Bdy and rgan mass and bdy cmpsitin f pstbreeding Lesser Scaup. Auk 104: 694-699. BAILEY, R.O. 1985. Prtein reserve dynamics in pstbreeding adult male Redheads. Cndr 87: 23-32. DEAN, W. R. J., & D. M. SKEAD. 1979. The weights f sme suthern African Anatidae. Wildfwl 30: 114-117. DOUTHWAITE, R.J. 1976. Weight changes and wing mlt in the Red-billed Teal Wildfwl 27: 123-127. DuBw¾, P. J. 1985. Seasnal rgan dynamics in pst-breeding male Blue-winged Teal and Nrthern Shvelers. Cmp. Blchem. Physil. 82 A: 899-906. FOLK, C., K. HUDEC, & J. TOUFAR. 1966. The weight f the Mallard (Anas platyrhynchs) and its changes in the curse f the year. Zl. Listy 15: 249-260. GAVRIN, G.F. 1970. Eclgical aspects f waterfwl multing in Kazakhstan. 8th Int. Cngr. Game Bil. Helsinki 1987. Finnish Game Res. 30: 74-77. HANSON, H. C. 1962. The dynamics f cnditin factrs in Canada Geese and their relatin t sea- snal stresses. Arctic Inst. Nrth Am., Tech. Pap. 12. KORTEGAARD, L. 1974. An eclgical utline f a multing area f Teal, Vejlerne, Denmark. Wildfwl 25: 134-142. LEBRET, T. 1971. Observatins f surface-feeding ducks (Anatidae) in wing mult in tidal habitat in the Biesbsh-Hllands Diep-Harringvliet-area. Limsa 44: 29-44. MAJEWSKI, P. 1981. Waterfwl ringing in Slnsk reserve (Pland). The Ring 106: 200-202. --. 1986. Breeding eclgy f the Mallard n a flded area f the Warta river muth, Pland. Wildfwl 37: 88-103. ORING, L.W. 1969. Summer bilgy f the Gadwall at Delta, Manitba. Wilsn Bull. 81: 44-54. OWEN, M., & R. KING. 1979. The duratin f the flightless perid in free living Mallard. Bird Study 27: 267-269. --, & M. A. OGILVIE. 1979. Wing mlt and weights f Barnacle Geese in Spitsbergen. Cndr 81: 42-52. PEHRSSON, O. 1987. Effects f bdy cnditin n mlting Mallards. Cndr 89: 329-339. ROWAN, M. K. 1963. The Yellwbill Duck Anas undulata Dubis in suthern Africa. Ostrich Suppl. 5. SHEWELL, E. L. 1959. The waterfwl f Barberspan. Ostrich Suppl. 3: 160-179. SJ SERG, K. 1988. The flightless perid f free-living male Teal Anas crecca in nrthern Sweden. Ibis 130: 164-171. YOUNG, D. A., & D. A. BOAG. 1981. A descriptin f mult in male Mallards. Can. J. Zl. 59: 252-259. ß & --. 1982. Changes in physical cnditin f male Mallards (Anas platyrhynchs) during mult. Can. J. Zl. 60: 3220-3226.