409
FEEDING BEHAVIOUR OF'BREEDING WIGEON Anas penelope IN RELATION TO SEASONAL EMERGENCE AND SWARMING BEHAVIOUR OF CHIRONOMIDS
ODD W. JACOBSEN
ABSTRACT Emergence ofchironomids started in mid-April, and reached a peak at the end of April and in the beginning of May. Most "spring" chiro nomids emerged around noon, whereas the majority of chironomids emerg ing later in the season, appeared at night. In general, there was a positive correlation between the seasonal emergencl~ of chironomids and gleaning frequency by individual Wigeon. Gleaning was observed exclusively on emergent vegetation in the morning and evening. During midday, gleaning occurred most frequently on water surface probably due to the diel emergence and swarming patterns ofchironomids. Gleaning was most frequently used by females, which is mainly due to their higher energetic requirements during the breeding seasons. I conclude that the increasing abundance of emerging chironomids in the spring is one important factor affecting time of nesting by Wigeon. Dept. of Animal Ecology, Museum of Zoology, University of Bergen, N 5007 Bergen, Norway.
INTRODUCTION several weeks and months before migration to the Arctic (Raveling 1979, Ankney 1984). Most dab Patterns in avian reproduction ultimately are adapt bling ducks, however, obtain their requirements ed to and proximately generated by variations in (lipids, proteins, minerals) for breeding by storing food supply (Lack 1966, Daan et al. 1988). In order reserves and by utilizing resources on their breed to understand avian breeding strategies, it is impor ing grounds (Drobney 1980, Krapu 1981). Although tant to know how resources are distributed in space recent studies have shown that food quality in the and time and how the birds obtain them during their non-breeding season may influence timing and re breeding cycle (Alisauskas & Ankney 1985). In productive output in ducks (e.g. Brodsky & Wea vestigations on wildfowl (Anseriformes) have de therhead 1985), little attention has been paid to con monstrated that females have much greater energy sider the relative importance ofhow availability of requirements than males during reproduction, and exogenous resources may affect timing ofbreeding that invertebrates account for a greater proportion (Drent & Daan 1980, Alisauskas & Ankney 1985). of the females' diet (Krapu 1981, Noyes & Jarvis The Wigeon Anas penelope is a medium-sized 1985, Ankney & Afton 1988). Krapu (1974) found dabbling duck. Wigeon has been considered as that the consumption of invertebrates increased vegetarian (Cramp & Simmons 1977), mainly be from 56% during prelaying to 77% during laying cause its main food on the wintering grounds con in the diet of Pintail Anas acuta. Wildfowl have sists ofgrasses, seeds and algae (Owen 1973, Owen evolved different strategies to store nutrients for & Thomas 1979, Campredon 1984, van Eerden reproduction. Most arctic-nesting geese are unique 1984, Mayhew 1985, Rijnsdorp 1986). However, re among precocial birds because ofthe short season cent studies on their breeding grounds in western and harsh conditions that prevail on their breeding Norway have shown that Wigeon prey exclusively grounds. Reproductive output in these birds is de on chironomids when they emerge in large num pendent upon energy reserves which are stored bers. One could predict that Wigeon would vary
Received 7 May 1991, accepted 16 August 1991. ARDEA 79: 409-418 410 ARDEA 79 (3), 1991 their foraging effort during the breeding season The breeding season was divided into the fol according to abundance and biomass ofpotentially lowing phases (Dwyer 1975, Afton 1979): Pairs in available invertebrate prey, because invertebrates arriving flocks were considered to be in the spring are temporally and spatially variable (Kaminski & arrival phase until intraspecific intolerance result Prince 1981), The seasonal relationship between ed in their dispersal from the flock. They were de chironomid emergence and Wigeon foraging fined as being in the prelaying phase until the day behaviour is the subject of the present study. prior to laying of the first egg. Laying dates were estimated by using the first day ofincubation when females were seen in recesses for one or two hours. STUDY AREA AND METHODS Four nests were found so that the exact laying date couldbe backdated from the first day ofincubation. Description ofthe study area Behaviour ofWigeon pairs was recorded by fo Data were obtained at Lake Bjellandsvatn cal animal sampling (Altmann 1974), during which (59°33'N, 5°21 'E) in western Norway. The climate one pair was observed for as long as possible during is humid with mild winters. The lake is surrounded the light period of the day. I recorded the activity by farmland, with scattered stands of pine Pinus ofeach sex and assigned it to the activity categories silvestris, birch Betula pubescens and some planta used by Afton (1979). Feeding behaviour was di tions ofNorway spruce Picea abies. Upland fields vided into grazing (l): plucking and shearing leaves are dominated by heather Calluna vulgaris and or other parts ofterrestrial plants with the bill, sub scattered bushes of juniper Juniperus communis. surface feeding (2): feeding by parts of the body Lake Bjellandsvatn is 10.9 ha and shallow (maxi sub-merged and gleaning (3): picking objects from mum depth 3 m). The southern part of the lake is the water surface and/or from emergent vegetation. influenced by agricultural runoff, causing well de Birds were easilyrecognized by individual plumage veloped stands ofemergent vegetation, e.g. Carex characteristics. Males and females showed great rostrata, Phragmites communis and Equisetum variability in plumage characteristics on flanks, fluviatile. Among floating-leaved hydrophytes, head and back (see Cramp & Simmons 1977). Nymphaea alba andPotamogeton natans dominate completely. Otherplants, such as Glyceriafluitans, Sampling of chironomids Eriophorum angustifolium, Potamogeton pusillus The phenology of emerging chironomids was and Callitriche spp. form sparse stands. sampled throughout the breeding seasons with The most abundant chironomid species in the sweep nets (all years) and funnel traps in 1988. The lake are Chironomus annularius, C. (Camptochi funnel trap was pyramid shaped, and guided the ronomus tentans), C. pilicornis, Endochironomus emerging pupae into a jar fitted to the trap apex dispar, Microtendipes chloris, Einfeldia longipes, (Mundie 1971). The jar was in an inverted position Chryptochironomus psittacinus, Paratanitarsus and when sub-merged, the upper half was filled tenuis, Ablamesmyia monilis and Polypedilum with air and the lower part with water. Insects arundinetum. emerged through the water-air interface in the jar and were retained within it. Time budget The funnel traps were placedonthe bottom (0.5 Data were gathered from 4 pairs in 1983, one - 1m depth) at ten random locations. Each trap cov pair in 1984 and 3 pairs in 1988 during April- June. ered a bottom area of 0.5 m2. Traps were put out In order to minimize disturbance, observations every 4 or 5 days for 24 hrs throughoutthe breeding were made using binoculars (8 x40) and a telescope season in 1988. The trapped chironomids were pre (25-40x) from vantage points about 100 - 200 m served in 70% ethyl alcohol for later identification. from the lake. All behavioural data were recorded Seasonal variations of chironomids in emer on a portable tape recorder. gent vegetation was estimated from sweep net sam- Jacobsen: FEEDING BEHAVIOUR OF WIGEON 411
Data on diel variation of chironomids in the 800 ...... 1983 20 emergent vegetation were collected three times dur fr----o 600 p .... .- 15 ing the breeding seasons in 1983 and 1984 and four ~ .....--o;" times during the breeding season in 1988. Chironomids 400 ••d/ 10 .- were randomly collected in the emergent vegetation ___ 200 5 RESULTS ur::..-=-;;-;=----,r-~--;"M7":A~Y,-----,-~~---' 0 time of year Seasonal and diel emergence and swarming Fig.I. Seasonal variations in the total numbers ofchi behaviour ofchironomids ronomids in sweep nets (1983, 1984) and in sweep nets The emergence of chironomids started about and funnel traps (1988). Note the different scale on the Y-axis in 1984. Water temperature (stippled line) is plot mid April all years and peaked at mid May in 1983 ted and dates offirst egg laying are indicated by vertical arrows (? above vertical arrow in 1988 is ± 2 days). 160 1983 140 pIes (aperture 25 cm and mesh size 5 !lm). Sam 120 pling was done between 9.00 and 11.00 h a.m. ev (f) -0 "E 100 ery week in 1983 and 1984 and every 4 or 5 days in o c: 1988. Sweep nets were drawn through vegetation g 80 .c: belts consisting ofEquisetumfluviatile and Carex u o 60 rostrata, a regular feeding site of Wigeon during c: the breeding seasons. Ten samples were randomly 40 collected at different sites in the vegetation, and 20 each sample consisted of 3 rapid sweeps a 2 m. Since there was a positive correlation between chi o'-r--,--,--,--,--i--,--.-..--..--.---r-.-.-r-hr' 6 8 10 12 14 16 18 20 22 ronomids collected in funnel traps and sweep nets time of day during the breeding season in 1988 (r = 0.72, N = s Fig. 2. Diel variation in mean number (± SD) ofchiro 15, P < 0.005) (Fig. 1), I concluded that there also nomids collected in sweep nets from the emergent vege should be an association between emergence of tation (Carex rostrata and Equisetum fluviatile) three chironomids and numbers collected in sweep nets times during the breeding seasons in 1983 and in 1984 in 1983 and 1984. and four times during the breeding season in 1988. 412 ARDEA 79 (3), 1991 and at the end of April and early May in 1984 and Seasonal and diel variation in Wigeon gleaning 1988 (Fig. 1). Towards the end of May, there was behaviour a second, but lowerpeak ofemerging chironomids Mean date of arrival was 3 May (± 15 days) in in 1984 and 1988. Chironomids were, especially in 1983, 16 April in 1984 (one pair) and 18 April (± 9 May, extremely abundant in relation to the total days) in 1988. When the first pairs appeared, they numbers of invertebrates collected in funnel traps and sweep nets, making up more than 90% of the catches. AttheendofApril andthe second weekinMay, ,=0.823 most chironomids emerged around mid-day, but P 100 r=O.790 '=0.862 p 1983 M 42.3** 37.1 NS 20.6** 1457 • F 20.9 37.7 41.4 2418 o 100'--'=0-.-76-7 D 32.7** ------,,1""; 2 M 34.1 NS 33.2** 627 • '=0.670 F 21.2 37.7 41.1 1489 p<0.05 • • p grazed mostly on terrestrial vegetation in agricul whereas most gleaning occurred from the water sur tural areas and along lake shores. However, when face during mid-day and in the afternoon (Fig. 4). chironomids emerged in large numbers, individual There was a positive correlationbetweenthe diel birds switched feeding behaviourfrom grazing and catches ofchironomids in the vegetation (Fig. 2) and sub-surface feeding to gleaning. 7 of8 females for per cent gleaning by 3 of 4 females in 1983 and by aged proportionally more by means of gleaning than males during the breeding seasons (Table 1). In general, there was a positive correlation be tween the numbers of chironomids collected in 100 r=0.681 I$ ,=0.802 1 sweep nets during the breeding seasons and the pro NS p kindly assisted in the field in 1983 and 1984. The study resources, females are able to produce larger was supported financially by the University of Bergen clutches and thereby raise more young (Schoener and the Directorate for Protection and Management of 1971, Batt & Prince 1979). Bengtson (1972) found Nature. that the breeding success of dabbling and diving ducks were low if chironomids were scarce. The low numberofchironomids collectedin sweepnets REFERENCES in 1984 as compared to 1983 and 1988 may probably explain why only one Wigeon pair "settled" in the Afton, A.D. 1979. Time budget of breeding Northern Shovelers. Wilson Bull. 91:42-49. lake this year, and why there was a longer period A1isauskas, R.T. & C.D. Ankney 1985. Nutrient reserves between peak abundance of chironomids and lay and the energetics of reproduction in American ing date in 1984 than in 1983 and 1988 (Fig. 1). Coots. Auk 102:133-144 Despite the fact that gleaning frequencies in fe Altmann, J. 1974. Observational study of behaviour: males were significantly higher than their mates, Sampling methods. Behaviour 49:227-267. Ankney, C.D. 1984. Nutrient reserve dynamics ofbreed the sexes responded, however, in a similar way by ing and molting Brant. Auk 101:361-370. gleaning throughout the breeding season (Fig. 3) Ankney, C.D. & A.D. Afton 1988. Bioenergetics of and throughout the day (Fig. 5). The most likely breeding Northern Shovelers: Diet, nutrient re explanation to this fact is that a male and female serves, clutch size, and incubation. Condor 90:459 Wigeon are closely associated to each other and 472. Aschroft, RE. 1976. A function of the pairbond in the thus feed in the same microhabitats during the Common Eider. Wildfow127:101-105. breeding season. The constant attendance of the Batt, B.D.J. & H.H. Prince 1979. Laying dates, clutch Wigeon male is an important factor to the female's size and egg weight ofcaptive Mallards. Condor 81: attempt to feed undisturbed and increase her daily 35-41. food intakeduring the breedingphases (M. Ugelvik Bengtson, S-A. 1972. Reproduction and fluctuations in the size of duck populations at Lake Myvatn, Ice pers. comm.). Similar arguments have been out land. Oikos 23:35-58. lined for other ducks, e.g. CommonEiderSomate Brodsky, L.M. & P.J. Weatherhead 1985. Time and ener ria mollisima (Ashcroft 1976) and Mallard (Mjel gy constraints on courtship in wintering American stad & S Driver, EA, L.G. Sugden & RJ. Kovach 1974. Calo Palmen, E. 1955. Diel periodicity ofpupal emergence in rific, chemical andphysical values ofpotential duck natural populations ofsome chironomids (Diptera). foods. Freshwat. BioI. 4:281-292. Suom. Elain-ja Kasvitiet. Seuran Vanamon Julk. 17: Drobney, RD. 1980. Reproductive bioenergetics of 1-30. Wood Ducks. Auk 97:480-490. Raveling,D.G.1979. The annual cycle ofbody composi Drobney, RD. & L.H. Fredrickson 1979. Food selection tion of Canada Geese with special reference to by Wood Ducks in relation to breeding status. J. control of reproduction. Auk 96:234-252. Wildl. Manage. 43:109-120. Rijnsdorp, A.D. 1986. Winter ecology and food of Dwyer, T.J. 1975. Time budget of breeding Gadwalls. Wigeon in inland pasture areas in The Netherlands. Wilson Bull. 87:335-343. Ardea 74: 121-128. Eerden, M.R van 1984. Waterfowl movements in rela Reiss, E 1968. Okologische und systematische Unter tion to food stocks. In: PR Evans, J. Goss-Custard suchungen an Chironomiden des Bodensees. Arch. & WG. Hale (eds.) Coastal Waders and Wild Hydrobiol. 64: 176-323. fowl:84-100. Cambridge University Press. Schoener, T. 1971. Theory of feeding strategies. Am. Fisher, J. & S. Rosin 1968. EinfluB vonLichtund Tempe Rev. Ecol. Syst. 2:369-404. ratur auf die Schliipfaktivitat von Chironomus Siegel, S & N.J. Castellan 1988. Nonparametric statistics nuditarsus. Rev. Suisse Zool. 75:538-549. for the behavioral sciences. 399 pp. McGraw-Hill Hartman, G. 1985. Food of male Mallard, before and Book Comp., New York. during moult, as determined by faecal analysis. Sjoberg, K. & K. Danell1982. Feeding activity ofducks Wildfowl 36:65-71. in relation to diel emergence of chironomids. Can. Jonasson, P.M. 1970. 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The sex-ratios and the proportion of Syrjamaki, J. 1964. Swarming and mating behaviour of adult drakes of Teal, Pintail, Shoveler and Wigeon Allochironomus crassiforceps. (Kieft). Ann. Zool. in The Netherlands, based onfield counts made dur Fenn.2:145-152. ing autumn, winter and spring. Ardea 38:1-18. Thomas, G.J. 1982. Autumn and winter feeding ecology Mayhew, P. 1985. The feeding ecology and behaviour ofwaterfowl at the Ouse Washes, England. J. Zool. ofWigeon Anas penelope. Ph.D. thesis, University Lond.197:131-172. of Glasgow. Wartinbee, D.C. 1979. Diel emergence patterns of lotic Mjelstad, H. & M. Sretersdal1988. The effect ofdensity Chironomidae. Freshwat. BioI. 9:147-156. on time budget of breeding Mallard Anas platy rhynchos. Cinclus 11:11-18. Mundie, J. H. 1971. Insect emergence traps. In: W.T. Ed SAMENVATTING mondson & G.G. Winberg (eds.) A Manual on Methods in Assessment ofProduction in Fresh Wa De Smient, die tijdens het overwinteren in Nederland ters:80-108. Blackwell, Oxford. vrijwel uitsluitend plantaardig voedsel gebruikt, blijkt in Noyes, J.H. & RL. Jarvis 1985. Diet and nutrition of het broedgebied van het zuidwesten van Noorwegen een breeding female Redhead and Canvasback ducks in menu te hebben waarin chironomiden (vedermuggen, Nevada. J. Wildl. Manage. 49:203-211. niet-stekend) een zeer belangrijk onderdeel vormen. In Oliver, DR 1971. Life history of the Chironomidae. dat gebied ligthetbegin van hetuitkomenvan deze insec Ann. Rev. Entomol. 16:211-229. Owen, M. 1973. The winter feeding ecology ofWigeon ten rond het midden van april en wordt een piek in de at Bridgewater Bay, Sommerset. Ibis 115:227-243. aantallen bereikt omstreeks beginmei (Fig. 1). De mees Owen, M. & G. J. Thomas 1979. The feeding ecology te van de inhet voorjaarverschijnende chironomiden ko and conservation of Wigeon at the Ouse Washes, men rond het middaguur uit, maar later in het seizoen England. J. Appl. Ecol. 16:795-809. gebeurtdat vooral 's nachts. Inde vegetatie zijn de groot- Jacobsen: FEEDING BEHAVIOUR OF WIGEON 417 ste aantallen vooral in de vroege ochtend en avond te ochtend en de avond, maar ook van het oppervlak van vinden (Fig. 2). het water, vooral overdag rond de piek van uitvliegen In het algemeen blijkt er een duidelijk positief ver (Fig. 4). Wijfjes toonden deze vorm van fourageergedrag bandte bestaan tussen de met sleepnetten bepaalde dicht in het algemeen meer dan mannetjes (Tabell), wellicht heid van chironomiden en de frequentie waarmee indivi als gevolg van hun hogere energiebehoefte. duele Smienten deze insecten verzamelden, zowel wat De conclusie lijkt dan ook gerechtvaardigd dat de betreft de variatie in de loop van het seizoen (Fig. 3), als toenemende dichtheid van uitkomende chironomiden in die inde loop van de dag (Fig. 5). Datverzamelen gebeurt het voorjaareenbelangrijke invloed heeftop het moment vooral uit de vegetatie, en weI het meest gedurende de dat de Smient in staat is te beginnen met eileg (Fig. 1).