Incubation Rhythms of Ring-Necked Ducks ’

The Condor88:290-296 0 The CooperOrnithological Society 1986

INCUBATION RHYTHMS OF RING-NECKED DUCKS ’

WILLIAM L. HOHMAN~ Delta Waterfowl and Wetland ResearchStation, Rural Route 1, Portage la Prairie, MB RlN 3A1, Canada

Abstract. Incubation behavior of Ring-necked Ducks (Aythya collaris) was studied in northwestern Minnesota from 1978 to 1980. Incubation constancywas similar for all birds (85%), but recessduration and frequency differed for females nesting along cattail/open water edges(X = 47 min, 5.1 recesses/day)and in flooded sedge meadow (K = 73 min, 2.7 recesses/day)away from open-water feeding areas.Timing of recessesalso was influenced by nest site location. Nest attentivenessof Ring-necked Ducks apparently is influenced by nutrient reserve levels in females at the onset of incubation and food availability in wetlands used by breeding birds. My findings are consistent with Afton’s (1979, 1980) prediction that in smaller soecies. environmental factors increasinglyaffect anatid‘incubation rhythms, and they generally support his conclusion that the relationship of fasting endurance to body size has been very important in the evolution of avian incubation behavior. Key words: Ring-neckedDucks; Avthva . collaris; ecology,behavior; reproductive biology; incubation

INTRODUCTION anatids environmental factors should have more effect on incubation rhythms. The behavior of birds during incubation is an Ring-necked Ducks (Aythya collaris) are important aspect of their subsequent repro- small-bodied (500 to 900 g) inland diving ductive performance and success.Individuals ducks. They commonly nest in northern bog may improve hatching successby increasing marshes, wetlands characterized by low pri- nest attentiveness;however, investment by the mary production (Reader 1978). This paper parent(s) to meet the needs of developing em- examines the behavior of incubating Ring- bryos and to enhance hatching successmust necked Ducks and relates incubation behavior be weighed against risks (e.g., predation, de- to the breeding biology of the species. habilitation, or starvation) to future reproductive performance. STUDY AREA AND METHODS Ducks, geese,and swans(Anseriformes) ex- Breeding Ring-necked Ducks were studied hibit a wide rangeof incubation strategies(Kear from 1978 to 1980 on Roseau River Wildlife 1970). Eggslaid parasitically by some anatids Management Area (WMA) in northwestern (e.g., Black-headed Ducks, Heteronettaatri- Minnesota. Roseau River WMA is an im- capilla; Ruddy Ducks, Oxyura jamaicensis; poundment situated on the bed of glacial Lake and Redheads, Aythya americanaare incu- Agassizin the prairie/boreal-forest transition. bated by host species.Males and females share The management unit was described in detail incubation in Magpie Geese (Anserunassemi- by Hansen et al. (1980). palm&a), Whistling-Ducks (Dendrocygnini) The return of Ring-necked Ducks to north- and some swans (Anserini), but females incubate without male assistancein 133 of 144 westernMinnesota in early April coincideswith extant waterfowl species(Kear 1970). Whereas rapid snow melt and sheet-water formation on agricultural fields (Hohman 1984). Laying is large waterfowl species such as the Canada Goose (Brantacanadensis) utilize endogenous initiated from mid-May to mid-June with nutrient reserves and incubate at high con- broods usually appearing by the fourth week stancy (Cooper 1978, Raveling 1979, Aldrich of June. Nests are constructedover water along and Raveling 1983), nest attentivenessof small cattail/open water edgesand in flooded sedge waterfowl species is generally lower because meadow away (0.5 to 2 km) from open water they have reduced capabilities for storage of feeding areas. Nests were located by watching females fly nutrient reservesand must recessto feed. Lim- ited fasting endurance led Afton (1980) to pre- to their nests or by flushing hens during sys- dict that in smaller, as compared with larger, tematic searchesof the study area. Ring-necked Duck eggsrequire, on average, 26 days incubation to hatch, with hen and brood usually departing from the nest on the day after hatch I Received 20 May 1985. Final acceptance25 October (Mendall 1958). Day of incubation was esti- 1985. 2 Presentaddress: Department of Fisheriesand Wildlife, mated by back-dating from hatching date. Ter- University of Minnesota, 1980 Folwell Ave., St. Paul, MN minology (i.e., incubation constancy, nest at- 55108, USA. tentiveness, recess frequency and length,

I2901 RING-NECKED DUCKS INCUBATION 291

TABLE 1. Incubation rhythm components of nine Ring-necked Duck females recorded in northwestern Minnesota, 1978 to 1980. Components given are for all nests combined, and by two habitat types.

Component MeaIl SE Median n Range

Incubation constancy(% of day) 85.2 0.4 85.4 197 68.7-100 Sedgemeadow 86.1 0.4 86.7 142 69.8-98.6 Open-water edge 83.1 0.9 84.0 55 68.7-100 Total time off nest per day (min) 212.7 6.0 210 197 O-450 Sedgemeadow 200.6 6.0 192 142 20-435 Open-water edge 244.0 12.8 230 55 O-450 Recessfrequency per day 3.4 0.1 33 197 O-9 Sedgemeadow 2.7 0.1 142 l-7 Open-water edge 5.1 0.2 5 55 O-9 Duration of all recesses(min) 62.4 1.2 60 716 5-315 Sedgemeadow 73.1 1.7 70 421 5-315 Open-water edge 47.1 1.2 45 295 lo-120 Duration of AM recesses(min) 52.5 1.4 zi, 307 5-170 Sedgemeadow 57.1 2.1 163 5-170 Open-water edge 47.3 1.6 45 144 lo-120 Duration of PM recesses(min) 69.8 1.8 65 409 5-315 Sedgemeadow 83.2 2.3 78 258 5-315 Open-water edge 46.9 1.6 45 151 lo-115 Sessionduration (min) 365.0 11.2 267 708 lo-2,095 Sedgemeadow 459.8 15.1 395 414 15-1,560 Open-water edge 231.5 13.1 155 294 lo-2,095

sessionlength) used in this paper follows that significantcorrelations were found between the of Afton (1980). day of incubation and incubation rhythm com- Presenceor absenceat the nest was detected ponents: nest attentiveness, recessfrequency, and recorded using a remote infrared therm- recesslength and sessionlength (P > 0.05). istor sensorsystem (Cooper and Afton 198 1). Ring-necked Duck incubation rhythms ap- Only data from complete day recordswere used peared to be influenced by nest site location. to calculate constancy and frequency of re- Birds incubated at similar constancyat cattail/ cesses/day.The relationship between day of open-water edge and sedge-meadownest sites incubation and incubation rhythm compo- (P > 0.05), but females nestingat cattail/open- nents (nest attentiveness,recess frequency, re- water edge sites adjacent to feeding areas recesslength, and sessionlength) was examined cessedmore frequently (P < 0.05) for shorter for the complete data set by using simple cor- durations (P < 0.05) than did females nesting relation analysis.The distribution of recessini- in sedgemeadow (Table 1). Timing of recesses tiation times by habitat or year was compared was also influenced by nest site location (P < usinga two-sided k-sample Smirnov test (Con- 0.01). Females nesting at cattail/open-water over 1980). Multiple and pair-wise statistical edge sites tended to recess during daylight comparisons were performed using Kruskal- hours, while sedge-meadow nesters generally Wallis rank sums multiple comparisons tests took a predawn recessand one or two recesses and Mann-Whitney U-tests, respectively from 1200 to 2200 (Fig. 1). Morning recesses (Conover 1980). were shorter than those taken in the afternoon for sedge-meadow-nestingbirds (P < 0.001). RESULTS Incubation rhythms for a single individual Eleven nest records were obtained from nine nesting in sedge meadow (1978, 1979, and Ring-necked Duck females. Nest attentiveness 1980) varied from year to year (Table 2, Fig. of one hen was monitored in three consecutive 2). Incubation constancy was lower in 1980 years. An average of 18 complete day records than that recorded in the two previous years (median = 20; range, 8 to 22 complete day rec- (P < 0.05). Whereas frequency of recesses/day ords) were obtained per female. All monitored was similar in all years(P < 0.05), recesslength nests were successfulfirst-nest attempts initi- increased significantly in 1980 (P < 0.001). ated between 18 May and 22 June. Timing of recessesalso changedannually (P < Incubation constancyaveraged 85%, but fre- 0.02). This female took predawn recessesdur- quency, timing, and duration of recessesvaried ing 1979 and 1980, but only diurnal recesses greatly among individual hens (Table 1). No in 1978 (Fig. 2). 292 WILLIAM L. HOHMAN

Open Water Edge 1978 N-58 N - 304

Sedge Meadow

N=413

All Nests

HOUR OF DAY 8 10 12 14 15 FIGURE 2. Distribution of recessinitiation times for an HOUR OF DAY individual Ring-necked duck female monitored in three FIGURE 1. Distribution of recess initiation times for consecutiveyears, 1978 to 1980. Ring-necked Duck females nesting in cattail/open-water edge and sedge-meadowsites. Except for Black Ducks, Redheads, and cavity nesterssuch as Wood Ducks and Common Goldeneyes, nest attentiveness of anatids in- DISCUSSION creaseswith body size, as observed by Afton Incubation constancy for Ring-necked Ducks (1980). In general, birds have a substantialca- (this study) is similar to that reported (Afton pability for storage and utilization of energy 1980, Ringelman et al. 1982) for Northern reserves, primarily in the form of fat (Blem Shovelers(Anus clypeata) and American Black 1976). Large waterfowl species have a pro- Ducks (A. rubripes).Captive Trumpeter Swans portionately greatercapacity for fat storageand (Cygnus buccinator), Canada Geese, Wood retain sufficient reserves after laying to main- Ducks (Aix sponsa),and captive Mallard Ducks tain body metabolism throughout incubation (Anas platyrhynchos) incubate at greater than (Ankney 1984). Perhaps equally important, 90% constancy (Stewart 1962; Caldwell and large body size may enable individuals to de- Comwell 1975; Cooper 1978, 1979). Lesser fend themselves and their eggsagainst poten- Snow Geese (Chen caerulescens)and Com- tial predators. Other factors, especially avail- mon Eider (Somateria mollisima), which fast ability of food to females during incubation, during incubation (Milne 1976, Ankney and influence incubation behavior as well. Contin- MacInnes 1978), alsoprobably incubate at high uousincubation is important in tundra-nesting constancy (> 90%); however, Green-winged waterfowl in preventing nest loss to avian Teal (Anas crecca carolinensis), Blue-winged predators (Ryder 1970, Harvey 197 1, Mac- Teal (Anas discors),Redheads, Ruddy Ducks, Innes et al. 1974). Body reserves of Brant and Maccoa Ducks (Oxyura maccoa) incubate (Bran& bernicla) at the onset of incubation are at less than 82% constancy (Low 1945, Miller insufficient to permit constant incubation 1976, Siegfried et al. 1976, Afton 1978). Es- (Ankney 1984). Brant delay reproduction and timates of incubation constancy for Common nest in areas that provide new green vegeta- Goldeneyes (Bucephala clangula) range from tion. This enables recessing females to feed 75% (Siren 1952) to 85 to 89% (Semenov-Tyan- near the nest while remaining vigilant against Shanski and Bragin 1969). potential nest predators (Ankney 1984). Fa- RING-NECKED DUCKS INCUBATION 293

TABLE 2. Incubation rhythm components of an individual Ring-necked Duck hen monitored in three consecutive years (1978-l 980) in northwestern Minnesota.

Mean k SE Comtwnent 1978 1979 1980

Incubation constancy(% of day) 87.6 + 0.9 86.7 + 1.1 82.5 + 0.9 n 22 8 22 Recessfrequency per day 2.3 -t 0.2 2.6 ? 0.2 2.6 * 0.1 n 22 8 22 Duration of all recesses(min) 76.3 k 3.0 72.0 * 3.7 97.7 ?z 3.3 n 58 25 59 Sessionduration (min) 534.7 + 54 515.2 f 58 459.6 f 37 n 55 24 59

vorable nest microhabitat (i.e., lower rate of to 90%, whereas Ring-necked Duck females egg cooling) and reduced predation risks pre- fed 57% of the time they were off the nest (W. sumably allow cavity nesters to spend more L. Hohman, unpubl.). The diet of Ring-necked time away from the nest, but high nest atten- Duck females during incubation consisted tiveness (93%) relative to body size in Wood mostly of invertebrate foods, especially cad- Ducks may shorten the incubation period disflies (Trichoptera), whose density and bio- (Breckenridge 1956) and also may be impor- mass changed seasonallyand annually (Hoh- tant in repelling parasitic laying attempts by man 1984, 1985). My hypothesis that other hens (Clawson et al. 1979). Food re- environmental food resourcesand body con- sources consumed by recessing Wood Duck dition of Ring-necked Duck females influence hens must be abundant and of high quality to incubation constancy is supported by annual permit constancy at such high levels because, variation in nest attentivenessof an individual in spite of high nest attentiveness,weight loss female. Nest attentivenessfor this female was by Wood Duck hens during incubation (11 O/o) significantly reduced in 1980, a year in which is less than that reported for other anatids birds entered reproduction at reduced body (Drobney 1982, Gatti 1983). Ringelman et al. weights and remained lighter throughout re- (1982) attributed low constancy(86%) in Black production, and invertebrate biomass during Ducks to small endogenousenergy reserves and the period birds were incubating (June) was the increased foraging time required by fe- depressed(Hohman 1984, 1986). males nesting in wetlands with low food den- Evidence linking nutrient reserve levels in sity. Becauseof limited metabolic reserve ca- incubating females to their nest attentiveness pacity and specializedfeeding habits, Northern is available for several other waterfowl species. Shovelers incubate at only 85% constancy Diurnal recess time of Redheads during (McKinney 1970, Afton 1980). Redheads are drought years was 25% greater than that ob- semiparasiticegg-layers; lower constancy(73%) served during a wet year (Sayler 1985). Sayler in this speciesmay be related to high levels of (1985) attributed lower nest attentivenessdur- disturbance at the nest and reduced maternal ing drought to reduced food abundance and investment in the incubated clutch, as well as lower endogenous reserves in breeding Red- environmental factors (Low 1945). head females. Female Canada Geese nesting I believe that incubation constancyof Ring- for the first time began incubation at a lighter necked Ducks is strongly influenced by nu- body weight and were less attentive than ex- trient reserve levels at the onset of incubation periencedfemales (Aldrich and Raveling 1983). and food availability in the wetlands used dur- Renesting waterfowl have depleted energy re- ing recesses.Ring-necked Duck females de- serves(Krapu 1974, Krapu 198 1) and incubate plete nutrient reserves during laying and thus at lower constancy than initial-nesting birds are almost entirely dependent during incuba- (Low 1945, Afton 1978, Afton 1980). Gatti tion on ambient food resourcesfor their met- (1983) found seasonaland annual variation in abolic requirements (Hohman 1986). Ring- body weight loss by incubating Mallards and necked Duck females feed intensively during speculatedthat condition of females at the on- incubation recesses,as do other small-bodied set of incubation may be an important factor waterfowl. The proportion of time spent feed- affecting nest attentiveness. ing by recessing Black Duck (Seymour and Ambient temperature was the most impor- Titman 198 l), Mallard (Titman 198 l), Blue- tant factor affecting Mallard incubation winged Teal (Miller 1976) and Northern rhythms (Caldwell and Cornwell 1975). Afton Shoveler (Afton 1979) hens averagedfrom 60% (1980) suggestedthat Northern Shoveler hens 294 WILLIAM L. HOHMAN

remained at the nest from 1000 to 1300 to sedge-meadow-nesting females. Because of protect the eggsfrom solar radiation and high rapid egg cooling and the inefficiency of re- midday temperatures,which could kill the em- warming eggs (Drent 1973), the incubation bryos (Snart 1970). Heavy rainfall modified pattern followed by cattail/open-water nesting incubation rhythms of both Mallards and birds of frequent, short recessesis probably Northern Shovelers (Caldwell and Cornwell more energy costly than that of sedge-meadow 1975, Afton 1980). These environmental fac- nesters (i.e., infrequent, long recesses). Re- tors (ambient temperature, solar radiation and cessingduring daylight hours when ambient rainfall) appear to have relatively little effect temperatures are elevated and covering eggs on Ring-necked Duck incubation rhythms. with nest material may help reduce the rate of Ring-necked Duck females recessed at night egg cooling (Caldwell and Cornwell 1975). (2200 to 0500) when ambient temperatures Moreover, females nesting adjacent to open- were lowest and at midday when solar radia- water feeding sites may benefit through lower tion was most intense. Moreover, I have ob- costs (time and energy) moving to and from served incubating females recessing during feeding areas. Ringelman et al. (1982) found moderate rain showers. differencesbetween the incubation rhythms of Timing of recessesmay be influenced by the Black Ducks nesting near wetlands and at up- behavior of their invertebrate prey. Northern land sites. Hens nesting at upland sites took Shovelersfeed extensively on planktonic crus- less frequent but longer recessesthan wetland taceans,Cladocera (Swanson and Nelson 1970, nesters.The rate of energyexpenditure by Black Swansonand Sargeant 1972), many of which Ducks in flight is over ten times greater than undergo die1 vertical migrations within the the estimated cost of incubating and rewarm- water column (Cushing 195 1). Recessestaken ing a clutch (42.7 vs. 3.8 kcal/hr). Ringelman before sunriseand at sunsetby Northern Shov- et al. (1982) hypothesized that upland-nesting elers may be a responseto higher food avail- birds compensate for increased flight costsby ability (Afton 1980). Invertebrates eaten by taking fewer, longer recesses. incubating Ring-necked Ducks are not known Ruddy Duck nestsare constructedover water to show die1 migrations, but females recessing in stands of emergent vegetation in semiper- before sunrise and at sunset may feed oppor- manent/permanent wetlands(Gray 1980). Like tunistically on emerging insects. Peak feeding cattail/open-water-edge nesting Ring-necked activity of breeding ducks on a northern Swed- Ducks, incubation rhythms of Ruddy Duck ish lake coincided with periods of chironomid females are characterized by frequent, short emergence (Sjoberg and Dane11 1982). Swan- recesses(Siegfried et al. 1976, Cooper and Af- son and Sargeant(1972) noted that nighttime ton 198 1). Siegfried et al. (1976) suggestedthat (2 100 to 0400) feeding activity of ducksbreed- 30 to 60 min was adequate for Ruddy Ducks ing in the prairies of North Dakota appeared to feed to the capacity of the esophagusand to be correlated with time and intensity of chi- proventriculus, but this probably is not true ronomid and mayfly (Ephemeroptera) emer- for Ring-necked Ducks. My estimates of food gences. consumption rate for Ring-necked Ducks are Predation also may influence incubation be- one-third to one-half those reported for Ruddy havior of Ring-necked Ducks. Low recessfre- Ducks (Gray 1980, Tome 198 1, Hohman quency and initiation of recesseswhen light is 198 5). Nonetheless,because of their proximity dim may be advantageousfor Northern Shov- to open water feeding areas, females nestingat elers in reducing the likelihood that a predator edge sites probably are able to better assess would discover the nest by sight (Afton 1980). changesin food availability and exploit tem- Patterns of recess initiation times for Ring- poral abundancesof foods (e.g., emerging in- necked Ducks nesting in the sedge-meadow sects).Disturbance from other birds using the and Northern Shovelers (Afton 1980) are sim- open water area (e.g., courting males) also may ilar. Ring-necked Ducks nesting in sedge- influence incubation patterns of edge nesters. meadow must fly to and from feeding areas If hens nesting at the edge of open-water and may be subject to predator constraints feeding areas are able to minimize behavioral similar to those of nestingNorthern Shovelers. costs and optimize foraging (and thereby re- Females nestingat the cattail/open-water edge duce risks of dehabilitation or starvation) while recess throughout daylight hours. They may maintaining incubation constancy, then why be able to do so because they can swim to do birds nest in the sedgemeadow? Unfortu- feeding areas and, therefore, may be less sus- nately, I lack sufficient data to assessthe rel- ceptible to predator detection. ative successof birds nesting in the two hab- Although birds incubated at similar con- itats, but I speculate that nests located at the stancy in both habitats, costs of incubation cattail/open-water edge are subject to greater probably differ for cattail/open-water edgeand risks of predation than nests dispersed in the RING-NECKED DUCKS INCUBATION 295 sedgemeadow. Gates and Gysel(l978), study- ANKNEY,C. D., AND C. D. MACINNES. 1978. Nutrient ing nest dispersion, clutch size and fledging reserves and reproductive performance of female successof 21 speciesof passerinesin relation Lesser Snow Geese. Auk 95:459-471. BIDER.J. R. 1968. Animal activitv in uncontrolled ter- to field-forest ecotones, found increased pre- r&trial communities as determined by sand transect dation rate with decreaseddistance from edge. technique. Ecol. Monogr. 38:269-308. This they attributed primarily to a functional BLEM,C. R. 1976. Patterns of lipid storageand utiliza- responseby predators to greater nest density tion in birds. Am. Zool. 16:67l-684. BRECKENRIDGE,W. J. 1956. Nesting study of Wood and predator activity in the vicinity of habitat Ducks. J. Wildl. Manage. 20: 16-21. discontinuities. The raccoon (Procyon lotor) is CALDWELL,P. J., AND G. $ CORNWELL.1975. Incuba- an important predator on nestsof Ring-necked tion behavior and temperaturesof the Mallard Duck. Ducks (W. L. Hohman, unpubl.) as well as Auk 92~706-731. those of other over-water-nesting waterfowl CLAWSON,R. L., G. W. HARTMAN,AND L. H. FREDRICK- SON. 1979. Dump nestingin a Missouri Wood Duck species(Stoudt 1982). In upland habitats, rac- population. J. Wildl. Manage. 43:347-355. coon foragingactivity focuseson ecotonal areas CONOVER,W. J. 1980. Practicalnonparametric statistics. (Bider 1968). Advantagesassociated with nest- John Wiley & Sons, New York. ing away from ecotonal areas, however, may COOPER,J. A. 1978. The history and breeding biology of Canada Geese of Marshy Point, Manitoba. Wildl. be offset by increased mortality of offspring Monogr. No. 61. after hatch, e.g., duckling mortality resulting COOPER,J. A. 1979. Trumpeter Swan nestingbehaviour. from long distance brood movements (Rin- Wildfowl 30:55-71. gelmanet al. 1982). I proposethat reservelevels COOPER,J. A., AND A. D. AFTON. 1981. A multiple sensor of birds entering reproduction influence nest systemfor monitoring avian nestingbehavior. Wilson Bull. 93:325-333. site selectionand predisposesome individuals GUSHING,D. H. 1951. The vertical migration of plank- (those with low metabolic reserves) to take tonic crustacea.Biol. Rev. 26: 158-192. greater risks (i.e., selectnest sitesclose to open- DRENT,R. H. 1973. The natural history of incubation, water feeding areas). Female experience also p. 262-311. In D. S. Famer [ed.], Breeding biology of birds. National Academy of Sciences,Washington, may influenceincubation rhythms (Aldrich and DC. Raveling 1983) and settlement patterns. DROBNEY,R. D. 1982. Body weight and composition In conclusion, environmental factors play changesand adaptations for breeding Wood Ducks. an important role in shapingRing-necked Duck Condor 84:300-305. incubation strategies. Because of body size GATES,J. C., AND L. W. GYSEL. 1978. Avian nest dispersion and fledging successin field-forest ecotones. constraintson nutrient storagecapabilities, en- Ecology 59:87 l-883. vironmental factors impacting female nutrient GATTI,R. C. 1983. Incubation weight lossin the Mallard. reserve levels at the onset of incubation and Can. J. Zool. 61:565-569. female energy expenditure during incubation GRAY, B. J. 1980. Reproduction energeticsand social structure of the Ruddy Duck. Ph.D.diss., Univ. of are especially influential on the incubation be- California, Davis. havior of small waterfowl species(Afton 1980). HANSEN,J. L., J. M. PARKER,AND K. R. HENNINGS. 1980. Roseau River Wildlife Management Area Master ACKNOWLEDGMENTS Plan, 1980-89. Minnesota Department of Natural Resources,St. Paul. I am grateful to R. D. Crawford, L. L. Hawkins and M. HARVEY,J. M. 1971. Factors affecting Blue Goose nest- W. Weller for their helpful comments on earlier drafts of ing success.Can. J. Zool. 61:565-369. the manuscript. I was assistedin the field or laboratory HOHMAN.W. L. 1984. Asoects of the breeding bioloav by J. Barzen, D. Carlson and J. Dixon. J. A. Cooper gen- of Ring-necked Ducks -(Aythya collaris). Ph.D.di&, erously shared his nest monitoring equipment with me. Univ. of Minnesota, St. Paul. Financial support was provided by the North American HOHMAN,W. L. 1985. Feeding ecology of Ring-necked Wildlife Foundation through the Delta Waterfowl and Ducks in northwesternMinnesota. J. Wildl. Manage. Wetlands ResearchStation, by the Minnesota Department 49:546-557. of Natural Resources,by the University of Minnesota De- HOHMAN,W. L. 1986. Changesin the body weight and partment of Fisheries and Wildlife, Computing Center, body composition of breeding Ring-necked Ducks Agricultural Experiment Station, and Graduate School, (Aythya collaris). Auk 103:181-188. and by the Minnesota Waterfowl Association. KEAR, J. 1970. The adaptive radiation of parental care LITERATURE CITED in waterfowl, p. 357-392. In J. H. Crook [ed.], Social behavior in birds and mammals. Academic Press, AFTON,A. D. 1978. Incubation rhythms and egg tem- New York. peraturesof an American Green-winged Teal and re- KRAPU, G. L. 1974. Feeding ecologyof Pintail hens dur- nesting Pintail. Prairie Nat. 10:115-l 19. ing reproduction. Auk 91:278-290. AFTON,A. D. 1979. Time budget of breeding Northern I(RApu, G. L. 1981. The role of nutrient reserves in Shovelers.Wilson Bull. 9 1:42-49. Mallard reproduction. Auk 98:29-38. AFTON,A. D. 1980. Factorsaffecting incubation rhythms Low, J. B. 1945. Ecology and management of the Red- of Northern Shovelers.Condor 82: 132-l 37. head, Nyroca americana, in Iowa. Ecol. Monogr. 15: ALDRICH,T. W., AND D. G. RAVELING. 1983. Effects of 35-69. experience and body weight on incubation behavior MACINNES,C. D., R. A. DAVIS, R. N. JONES,B. C. LIEFF, of Canada Geese. Auk 100:670-679. AND A. J. PAKULAK. 1974. Reproductive efficiency ANKNEY, C. D. 1984. Nutrient reserve dynamics of of McConnell River small Canada Geese. J. Wildl. breeding and molting Brant. Auk 101:361-370. Manage. 38~686-707. 296 WILLIAM L. HOHMAN

MCKINNEY, F. 1970. Displays of four speciesof blue- SIEGFRIED,W. R., A. E. BURGER,AND P. J. CALDWELL. winged ducks. Living Bird 9:29-64. 1976. Incubation behavior of Ruddy and Maccoa MENDALL,H. L. 1958. The Ring-necked Duck in the ducks. Condor 78:5 12-5 17. Northeast. Univ. of Maine Studies,Second Series 73. SIREN, M. 1952. Undersijkningar iiver knipans, Bu- MILLER,K. J. 1976. Activity patterns,vocalizations, and cenhaluclanmla, fortvlantninabiologi. Riistatiet. Jul- site selection in nesting Blue-winged Teal. Wildfowl kaisuja8:10i-111. _ - -’ 27~33-43. SIBBERG, K., AND K. DANELL. 1982. Feeding activity of MILNE, H. 1976. Body weights and body composition ducks in relation to die1 emergenceof chironomids. of the Common Eider. Wildfowl 27: 115-122. Can. J. Zool. 1383-1387. RAVELING,D. G. 1979. The annual cycle of body com- SNART,A. E. 1970. The effects of heat on Mallard em- position of Canada Geese with special reference to bryos. M.S.thesis, Univ. of Florida, Gainesville. control of revroduction. Auk 96:234-252. STEWART,P. A. 1962. Nest attentivenessand incubation READER,R. J. 1678. Primary production in northern bog period of a Wood Duck, J. Field Omithol. 33:85-89. marshes, p. 53-62. In R. E. Good, D. F. Whigham, STOUDT,J. H. 1982. Habitat use and productivity of and R. L. Simpson [eds.], Freshwater wetlands: eco- Canvasbacksin southwesternManitoba, 1961-1972. logical processesand management potential. Aca- U.S. Fish Wildl. Serv. Spec. Publ. No. 248. demic Press, New York. SWANSON. G. E.. AND H. K. NELSON. 1970. Potential RINGELMAN,J. K., J. R. LONGCORE,AND R. B. OWEN,JR. influknce of fish-rearing programs on waterfowl 1982. Nest and brood attentivenessin female Black breeding habitat, p. 65-71. In E. Schneberger[ed.], Ducks. Condor 84:110-l 16. A symposiumon the managementof midwestem win- RYDER,J. P. 1970. A possiblefactor in the evolution of terkill lakes.Am. Fish. Sot., North Central Div., Spec. clutch size in Ross’ Goose. Wilson Bull. 82:5-l 3. Publ. SAYLER, R. D. 1985. Brood parasitism and reproduction SWANSON, G. A., AND A. B. SARGEANT.1972. Obser- of Canvasbacksand Redheads on the Delta Marsh. vation of nighttime feedingbehavior of ducks.J. Wildl. Ph.D.diss., University of North Dakota, Grand Forks. Manage. 36:959-961. SEMENOV-TYAN-SHANSKI,0. I., AND A. B. BRAGIN. 1969. TITMAN,R. D. 1981. A time-activity budgetfor breeding Incubation conditions for some precocialbirds in the Mallards (Anus &zt~~rhynchos)in Manitoba. Can. subarctic. Byull. Mosk. 0-Va. Ispyt. Prir. Otd. Biol. Field-Nat.‘95:266-2?1.. ’ 74150-66. TOME. M. W. 1981. The revroductive bioenereetics of SEYMOUR,N. R., AND R. D. TITMAN. 1981. Changesin female Ruddy Ducks in Manitoba. M.S.the&, Univ. activity patterns,agonistic behavior and territoriality of Maine, Orono. of Black Ducks (Anas rubripes) during the breeding seasonin a Nova Scotia tidal marsh. Can. J. Zool. 56:1773-1785.