hunting pressures (Raveling 1978, Frederick and Klaas 1982. Humburg et al. 1985 .... Energetic costs were then converted from watts to kilojoules per minute.
21
Diurnal Flight Time of Wintering
Canada Geese: Consideration of
Refuges and Flight Energetics
JANE E. AUSTIN! and DALE D. HUMBURG Gaylord Memorial Laboratory, School of Natural Resources,
University of Missouri, Puxico, MO 63960 (JEA)
Missouri Department of Conservation, Columbia, MO 65201 (DOH)
ABSTRACT - We monitored individual radio-equipped Canada geese (Branta canadensis) associated with a federal refuge to assess flight activities from late fall through spring. The number of flights per day was lowest in late fall when most geese remained within the refuge and highest in spring when they moved increasingly beyond the refuge area. The only significant seasonal difference in fli£ht time occurred between late fall and late winter 1986. Over all seasons, diurnal flight time ave~ged 9.4 ± 2.4 min (SE) and ranged from 0 to 33 min. Geese spent more time flying in afternoon periods during late winter 1986 and early winter 1987. Because of low goose populations on the refuge and abundant food resources in 1986-87. flight activity was probably lower than in most other years. Conservative estimates of average daily energy expenditures for flight ranged from 65 kJ/day in late fall to 200 kJ/day in early winter and were as high as 450 KJlday. Additional energy costs for flight, when expressed as a percentage of daily energy expenditures, increased from fall (3%) to spring (10%). Highest estimates total daily energy costs (2987 kJ/day, equivalent to 178 g corn)appear to be within reasonable estimates of daily energy consumption. During periods of severe cold or limited food availability, however. additional energy demands for flight (e.g.. due to disturbances or long foraging flights) may become important in the daily energy balance of individuals.
Key words: Branca canadensis. Canada geese, flight energetics, winter. refuge
Movements, activities, and distribution of migrant and wintering geese are often strongly influenced by the presence of refuges, primarily because of hunting pressures (Raveling 1978, Frederick and Klaas 1982. Humburg et al. 1985, Harvey 1987). During the hunting season, activity patterns of geese are altered, and movements are often limited to areas in and around refuges (Koerner et al. 1974, Zicus 1981, Frederick et al. 1987). After the hunting season, birds tend to forage farther from the refuge, and may establish new roost areas outside of refuges. This general pattern follows that outlined in the concept of "refuging" (Hamilton and Watt 1970, Frederick et al. 1987). Birds fIrst exploit foods nearest the core refuge area and, as foods nearby are depleted, they must move ever greater distances to meet their energy requirements. Energy gains must be greater than or balanced with the energy costs of moving to the feeding area. If the energy costs exceed gains, geese can move to a new core area where food is more plentiful. e.g., shifting a roost area or emigrating from the a r e a . I
Present address: u.s. Fish and Wildlife Service, Northern Prairie Wildlife Research Center, Rt. 1, Box 96C, Jamestown, ND 58401-9736
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Prairie Naturalist 24(1) March 1992
A large portion of migrant Canada geese winter farther north than they did traditionally, responding to increased availability of food, open water, and refuges (Humburg et al. 1985). These birds are more likely to encounter periods of severe conditions limiting their movements or foraging, such as snow or ice cover, than geese that winter in southern regions. The ability of geese to balance energy gains and expenditures may be constrained during these periods, de pending on food availability and distribution, weather. and disturbances. At such times the distance birds must move from a roosting area to feed may be come increasingly important. A direct measure of bird movements is time spent in flight. Flight is the most energetically costly activity of waterfowl (King 1974) and thus can be an important component of daily energy expenditures (DEE). Daily flight time has not been directly measured for waterfowl, although it has been estimated to be 0.5 hr for breeding American black ducks (Anas rubripes) (Wooley and Owen 1978), postbreeding redheads (Aythya americana) (Bailey 1981), and snow geese (Anser caerulescens) at a migration stop-over area (Frederick and Klaas 1982), and 1.3-1.5 hr for wintering and spring staging snow geese (Davis et al. 1989). More accurate determination of daily fight time would be helpful to assess overall daily energy expenditures or seasonal allocation of energy, espe cially during severe winter weather or the hunting season. A large proportion of migrant and wintering Canada geese (Branta cana densis) of the Eastern Prairie Population (EPP) are associated with managed state and federal refuges in the western portions of the Mississippi Flyway. ~any of the EPP geese migrate through or winter at Swan Lake National Wild life Refuge (NWR) in north central Missouri (Mississippi Flyway Council Technical Section 1986). We describe seasonal and daily patterns of diurnal flight time determined for individual Canada geese wintering on Swan Lake ~ during 1986-87, and evaluate daily energy expenditures of flight. STUDY AREA AND METHODS
The study area on Swan Lake NWR (4,318 hal and the surrounding private and state lands provided a variety of habitats for wintering waterfowl, including grain crops, winter wheat and other green forage. seasonal wetlands, and flooded timber. Further descriptions of the area are provided by Kahl (1980) and Austin (1988). Adult Canada geese were selected at random from cohorts captured with cannon-nets (Dill and Thornsberry 1950) in mid-November 1985 (8 males and 13 females), late October 1986 (9 males and 9 females), and early February 1987 (1 male and 1 female). These geese were marked with individually coded neck collars and fitted with back-mounted radio transmitters (Dwyer 1972) that had an effective range of 3-10 km. We monitored individual radio-marked geese during January-February 1986 and from November 1986 to early March 1987. Radio tracking began 7-10 days after geese were marked and continued through early March. We tracked geese 4-6 days each week using a vehicle equipped with a null-peak antenna system. On each tracking day, one radio
Austin and Humburg: Canada Geese
23
equipped goose was chosen at random, and its movements and flight times were monitored continuously from 30 min before sunrise to 30 min after sunset. We located geese immediately after each flight or change in signal direction. A sudden change in the signal volume and direction distinguished flight from other activities. We confirmed these changes by visual observations of the goose or flock when possible. If no apparent movement occurred within two hours after a location, the location of the goose was rechecked. We summarized total flight time and number of flights each day. Geese whose locations were unknown at the beginning or end of a day or for more than 2 hr during a day were excluded from analyses of daily activity. We summarized data each day for three periods: morning (30 min before sunrise-lOOO hr CST), mid-day (1000-1400 hr CST), and afternoon (1400 hr CST-30 min after sunset). We excluded observations of geese whose locations were unknown for more than 1 hour from analyses for that period. Four seasons were delineated based on temperature and ice conditions: (1) late fall November until freeze-up (1 Nov-23 Dec 1986); (2) early winter during freeze-up (24 Dec 1986-28 Jan 1987); (3) late winter - a period ofvari able freeze-thaw conditions (15 Jan-24 Feb 1986 and 28 Jan-22 Feb 1987): and (4) spring - after the final thaw (after 22 Feb 1987). The goose hunting season occurred entirely in late fall. Data were summarized for each season as average flight time per day and average number of flights per day (hereafter referred to as average flight time or average number of flights). Differences in average flight time and average number of flights among seasons and periods were tested using repeated measures analysis of variance (ANOV A) (Milliken and Johnson 1984:378-4(7) to account for the repeated observations of individuals among periods. If differ ences from Al\fOVA tests were significant, we used Scheffe's multiple compari son test to compare among seasons. Results were expressed as least square means. Conservative estimates of daily energy expenditures for flight IDEE F) were calculated from the flight times of geese in this study. The energetic costs of flight were calculated using the formula developed by Masman and Klaassen ( 1987): where et.::flight costs (W), M=body mass (g). bw=wing span (cm), and sw=wing area. Energetic costs were then converted from watts to kilojoules per minute. We calculated ef for each season and sex: because resulting values varied by less than Soc, we report the average ef of sexes combined. Sex- and season-spe cific values are presented in Appendix 1. We used average body mass of adult males (n=103) and females (n=101), by season, collected on Swan Lake NWR during 1983-87 (Austin, unpub!' data). Wing spans and wing areas were determined from hunter-killed adult geese during November-December 1991. Wing spans of males (n=26) and fe males (n=16) averaged 146.7 ± 1.1 cm (x ± SE) and 144.1 ± 1.8 cm. respective ly. Wing areas of males and females averaged 2920 ± 56 cm2 and 2998 ± 137 cm'. respectively. Wing measurements were not Significantly different between sexes (t-test. P > 0.05).
Prairie Naturalist 24(1) March 1992
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Williams and Kendeigh (1982) estimated daily existence metabolism of adult male Canada geese in late fall (average ambient temperature ca. 9°C), early winter (ca. -19°C), and spring (ca. 5°C) at 1955,2537, and 2039 kJlbirdl day, respectively. These estimates, hereafter referred to as daily energy expendi ture (DEE), did not include flight activity. Body weights of geese from Wil liams and Kendeigh (1982) were similar to those used here (see Appendix 1). We used Storey and Allen's (1982) value of apparent metabolizable energy for com (16.81 kJ/g air-dry weight) to estimate energetic costs in terms of com consumption; all measures of com are expressed as air-dry weight. We estimated that geese fly about 1 kmImin (Frederick et al.1987, Austin 1988). .
RESULTS We monitored Canada Geese during 80 days, including 70 days of complete observations. Daily patterns of activities tended to vary from day to day, and no consistent patterns of activity were apparent for individuals. The number of flights per day was variable among days, ranging from 0 to 14 flights (Table 1). Some flights were very brief, such as when a goose flushed and landed in the same field following a disturbance or when it moved within a field. Average number of flights differed among seasons (F=5.564, 4, 75 df, P0.05i as analyzed using repeated measures ANOVA. bRange of values. cNo. bird-days'" 12.
Over all seasons, Canada geese averaged 9.4 ± 2.4 min (x ± SE) in flight each day. Although the interaction of season and period was marginally signifi cant (F = 2.025, 8, 136 df, P = 0.048), we compared average seasonal flight times using all periods. Seasonal differences in average flight time were signifi cant (F=6.370, 4, 77 df, P
