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 north- western 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 atten- tivenessof 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; incu- bation 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 reproduc- tive 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 in- cubate 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 incu- bation 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 re- cesslength, 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 cav- ity 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).