Effects of saline environments on the survival of wild goslings (Branta canadensis).
Fish Springs National Wildlife Refuge (Fish Springs NWR) was established in 1959 to provide nesting, wintering and migratory habitat for waterfowl. Creation of impoundments and other developments of the marshlands was completed in 1964. It is not known whether Canada geese (Branta canadensis) nested in this area before the establishment of the refuge (Annu. Rep., Fish Springs NWR, 1982; J. Banta, Fish Springs NWR, pers. comm.); however, they were not nesting in the refuge area in 1959. Refuge managers used a captive flock to entice wild geese to Fish Springs and, through release and unintentional escape of captives, established a year-round population. From 1989 to 1995 refuge personnel monitored breeding birds to obtain production numbers and survival rates (Table 1). Overall fledging success (weighted average) for these 6 y was 34% with annual gosling production averaging 26 (Fish Springs NWR records).
Populations of Canada geese generally experience higher fledging success rates than the 34% found at Fish Springs NWR (Table 2). Young birds raised in saline environments may be predisposed to mortality from other causes. For example, low gosling survival rates may be the result of stochastic events, e.g., disease epidemics (Sherwood, 1966), storms or unusual weather conditions (Sargeant and Raveling, 1992). Other causes of mortality include environmental contaminants (Blus et al., 1979; Ohlendorf et al., 1986; Stephens and Waddell, 1989; Sargeant and Raveling, 1992), predation (Geis, 1956; Brakhage, 1965; Sherwood, 1966; Mickelson, 1973: Wang, 1982; Sargeant and Raveling, 1992; Sedinger, 1992), human disturbance (Sherwood, 1966), inadequate nutrition (Sedinger, 1992) and poor parenting skills (Raveling, 1981; Afton and Paulus, 1992). Most gosling mortality occurs in the first 10 to 14 d following hatching (Geis, 1956; Steel et al., 1957; Martin, 1963; Dey, 1964; Brakhage, 1965; Mickelson, 1973; Krohn and Bizeau, 1980; Ball et al., 1981; Zicus, 1981; Eberhardt et al., 1989; Sargeant and Raveling, 1992).
TABLE 1. - Production and percent survival of Canada goose goslings at Fish Springs NWR, 19891995 Number nesting Goslings Goslings Percent Year pairs hatched fledged survival 1989 18 63 22 34.9 1990 19 65 33 50.7 1991 18 67 18 26.8 1992 22 95 31 32.6 1993 21 99 34 34.3 1994 No data 69 No data No data 1995 No data No data 17 No data Average 20 75 26 34.2
Adult geese and ducks are able to drink saline water because they possess nasal salt glands that excrete excess salt from the bloodstream. The kidneys alone are incapable of excreting sufficient salts to ensure the survival of a bird exposed to hypertonic saline drinking water (Bradley and Holmes, 1972). Goslings and ducklings develop fully functioning salt glands about 6 d after hatching (Ellis et al., 1963; Riggert 1977; D. Stolley, pers. obs.). Domestic [TABULAR DATA FOR TABLE 2 OMITTED] ducklings given solutions of NaCl experienced depressed growth (Ellis et al., 1963; Schmidt-Nielsen and Kim, 1964; Riggert, 1977; Wink and Hossler, 1979; Wink, 1980).
Field and laboratory studies established dosage responses of mallard (Anas platyrhynchos) and other ducklings to saline drinking water (Swanson et al., 1984; Mitcham and Wobeser, 1988a, b). Swanson et al. (1984) exposed 4 groups of 10, 1-d-old mallards to saline lake water diluted with nonsaline well water in 1000 [[micro]seconds]/cm increments from 17,000 to 20,000 [[micro]seconds]/cm for 9 d to determine effects on growth, measured by body mass. They compared results with data from ducklings given well water and found significantly reduced growth as specific conductivity increased. They observed no mortalities at 17,000 [[micro]seconds]/cm, 10% mortality at 18,000 and 19,000 [[micro]seconds]/cm and 30% at 20,000 [[micro]seconds]/cm. In a different experiment, they supplied 10, 1-d-old mallard ducklings with lake water measuring 16,000 [[micro]seconds]/cm for 12 d and recorded 10% mortality after 4 d. Mitcham and Wobeser (1988b) gave water from 10 saline Saskatoon wetlands to mallard ducklings under laboratory conditions. All ducklings given water with conductivities of 35,000 and 67,000 [[micro]seconds]/cm died within 60 and 30 h, respectively. They found 60% mortality at 20,000 [[micro]seconds]/cm by the sixth d of a 14-d trial; no additional mortalities occurred after the sixth d. Ducklings raised on water with conductivities ranging from 3750 to 7490 [[micro]seconds]/cm grew as well as control birds supplied with fresh water in 14-d trials. However, when those supplied with water measuring 4000 [[micro]seconds]/cm were monitored to day 28, they had a significantly lower growth rate during the second 14 d. We observed (Stolley et al., in press) that saline drinking water (12,000 [[micro]seconds]/cm) caused slower growth in captive wild-strain goslings. The daily mean values for body mass, wing length and culmen length for goslings given 12,000 [[micro]seconds]/cm water were consistently less than goslings given tap water. However, most of the differences were not statistically significant. We observed 33% mortality (n = 9) at 18,000 [[micro]seconds]/cm and statistically significant reductions in growth at 12,000 [[micro]seconds]/cm. We expected that free-ranging wild goslings would experience mortality at lower conductivities than laboratory birds because of other environmental stresses and the hazards of living in the wild, and would die soon after hatching. The literature supports this conjecture.
Fish Springs NWR is fed by moderately brackish springs; there is no fresh water in the marsh. The small amounts of rainfall this area receives are incorporated immediately into the larger bodies of saline water. In the brood-rearing impoundments preferred by geese, salinity levels can rise to sublethal and lethal levels. Thus, salinity is a potential cause of gosling mortality on the refuge.
We investigated the effects of naturally occurring saline conditions that goslings encountered from day 1 through day 15 on mortality levels. We (1) identified hydrologically distinct locations within the marsh and quantified salinity levels at each location during the breeding season, (2) determined daily the location and number of goslings in every brood from hatching through day 15 and (3) tested whether salinity of naturally occurring drinking water available to goslings was correlated with mortality.
Study area. - Fish Springs NWR is located at the southwest edge of the Great Salt Lake Desert in Juab County. Utah. The refuge is at an elevation of 1311 m, and receives an average of 20 cm of rain annually, although there is high variation from year to year. Temperatures range from -26.1 to 42.7 C. The refuge is 7282 ha and contains approximately 3604 ha of saline marsh, 2867 ha of mud and alkali flats and 811 ha of semidesert uplands. At optimum water level there are about 1416 surface ha of water in a complex of pools, sloughs and springs. As ancient Lake Bonneville lake bottom, the refuge is flat and the soil is saline and alkaline.
Five major and several minor thermal springs arise from a fault line running parallel to the east side of the Fish Springs Mountain Range and supply the refuge with water [ILLUSTRATION FOR FIGURE 1A OMITTED]. The springs are moderately brackish with specific conductivity measurements that range from 2900 to 3400 [[micro]seconds]/cm, except for North Spring which measured 5100 [[micro]seconds]/cm.
An aerial photograph taken before modification of the wetlands began (ca. 1960) shows an area of sloughs and narrow waterways lined with emergent marsh vegetation [ILLUSTRATION FOR FIGURE 1B OMITTED]. After the refuge was established in 1959 nine large shallow pools, impounded by dikes and fed from the springs through canals, were created, enlarging and modifying the natural marsh. Much of the area of the more southern impoundments, viz., Avocet, Mallard, Curlew, Egret and Shoveler, was part of the original slough and contains numerous islands and peninsulas. The southernmost impoundments are also closer to the springs that provide their water. Because of this, and because the soil underlying these impoundments is flushed continually with springs most of the year, the water in these pools is only slightly to moderately saline. The impoundments contain typical emergent marsh vegetation, e.g., Olney's three-square bulrush (Scirpus americanus), cattail (Typha domingensis), hardstem bulrush (S. acutus), alkali bulrush (S. maritimus), wirerush (Juncus arcticus) and saltgrass (Distichlis spicata). Abundant mats of vegetation, primarily wigeongrass (Ruppia maritima), muskgrass (Chara spp.), pond naiad (Najas marina) and coontail (Ceratophyultum demersum) grow in the springs, canals and pools. Additionally, Phragmites sp. has expanded into the marsh.
The northern impoundments, viz., Ibis, Pintail, Harrison and Gadwall were constructed on the northern edge of the original wetlands and contain little of the original marsh structure. Most of the water feeding these pools comes from the more southern pools. Because of evaporation and leaching of salts from the original playa the water in the northernmost impoundments is more saline than in the southern impoundments: salinities range from 4700 to over 25,000 [[micro]seconds]/cm during the breeding season (Fish Springs NWR unpub. records). These impoundments become dry or reduced during the summer because the volume of spring input does not match evaporation rates. The bordering vegetation is characterized by saltgrass (Distichlis spicata), pickleweed (Allenrolfea occidentalis) and annual samphire (Salicornia europaea). The pools contain little emergent or submergent vegetation.
To identify hydrologically distinct locations within the marsh and quantify the salinity levels of each location throughout the Canada goose breeding season, we measured salinity levels with a temperature-corrected specific conductivity meter (YSI model 30). From 15 April to 15 July 1997 we took weekly conductivity measurements at 17 water control structures along canals and at the edges of each impoundment.
To determine the location and number of goslings in every brood daily from hatching through day 15 after hatching, we found and marked adults in nine impoundments and found and monitored nests. We placed individually marked plastic neck collars on molting breeding adults and put radio-collars on nesting females when their eggs were pipping. We used telemetry and observations to locate broods. We conducted all observations and radio tracking from the dikes surrounding each impoundment.
We used a chi-square analysis to test the relationship between salinity of drinking water available to goslings and mortality. We first calculated daily estimates of specific conductivity at each of the 11 hydrologically distinct locations. We then classified each location on a daily basis as either low ([less than]8200 [[micro]seconds]/cm) or high ([greater than or equal to]8200 [[micro]seconds]/cm) conductivity areas. We chose 8200 [[micro]seconds]/cm as a dividing point because it was the approximate midpoint of the range of specific conductivities experienced by broods from day 1 to day 15 following hatching (range = 4000-12,230 [[micro]seconds]/cm) on our study site. Although no direct mortality has been documented below 12,000 [[micro]seconds]/cm, ducklings monitored to 28 d on 4000 [[micro]seconds]/cm had significantly lower growth rates (Mitcham and Wobeser, 1988b), predisposing them to other causes of mortality. Because there is virtually no data for goslings, we wanted to see if we could detect any effects at or above the mid-range of the salinities we recorded on our study site. We tabulated the day and location/conductivity classification of mortality for all deaths through day 15. We could not ascertain definitive cause of death because we observed no direct mortality nor did we recover any dead goslings. In our analysis we did not use records of goslings that we lost contact with for more than 2 d and who disappeared during that time. If a brood found mostly in high-conductivity locations was found in a low-conductivity location for more than 2 d, or vice versa, we did not use it in the analysis. We also looked at the effect of gosling location on mortality by calculating the number of gosling deaths per use-day at each location.
Specific conductivity. - Eleven of the 17 water control structures monitored were hydrologically distinct areas (Table 3) within the 9 impoundments (2 impoundments, Curlew and Gadwal, had discrete north and south pools separated by land and filled by different water sources). In many of the impoundments specific conductivity increased from the inflow area to the outflow area. Since we were not sure where the goslings drank within the pools, we used the lower measurements for conservative estimates. From 15 April to 15 July 1997 conductivity measurements ranged from 3080 to 25,350 [[micro]seconds]/cm within these areas (Table 3). [ILLUSTRATION FOR FIGURE 3 OMITTED] The general trend for all but three locations (Avocet, Mallard and S. Curlew) was an increase in salinity as the season progressed. Conductivity measurements for these three southernmost impoundments which received water more directly from the springs remained within [+ or -]400 [[micro]seconds]/cm of the first measurements of the season.
Brood location and gosling mortality. - There were 20 broods at Fish Springs NWR in 1997. One brood was not used because we did not see it until the goslings were approximately 41-d-old; thus we monitored 19 broods from hatching through day 15 after hatching; 7 broods were with females wearing coded collars and radio transmitters, 5 broods were with 1 or more collar-marked parents and 7 broods were with unmarked parents; we identified those broods by age of goslings and location. The first brood hatched on 25 April, the last on 25 May. From day 1 to day 15 after hatching, the broods used locations with specific conductivities ranging from 4200 to 12,400. Nine of the 19 broods remained on the impoundment where they hatched for the full 15 d. Three broods went to 1 other location, 7 broods used 3 or more locations. The 19 broods contained 77 goslings on hatch day. Eleven deaths occurred before day 2; 24 more deaths occurred from day 2 through day 15. These 35 deaths accounted for 87.5% of all prefledgling gosling mortalities at the refuge in 1997.
We compared gosling mortality to specific conductivity of location with data from 15 of the 19 broods. Two broods of 1 gosling each were not used because the goslings either died or disappeared on day 1; we suspected that predation was responsible. Two other broods were not used because they were in unknown locations for more than 2 d each. The 15 broods we analyzed contained a total of 63 hatched goslings; 27 died before day 16.
We used a chi-square analysis to test the null hypothesis that gosling mortality from hatching through day 15 was independent of salinity classification (Table 4). If salinity was responsible for the mortalities, we expected more deaths in the high conductivity group. Although we rejected the null hypothesis ([[Chi].sup.2] = 9.35, P = 0.0093) we found more mortalities in the low conductivity group. Thus, high salinity was not correlated with higher levels of gosling mortality.
TABLE 4. - Comparison of mortality from day 1 to day 15 of Canada goose goslings at high ([greater than or equal to]8200 [[micro]seconds]/cm) and low ([less than]8200 [[micro]seconds]/cm) conductivity, locations at Fish Springs NWR, 1997, using a chi-square test of independence(a) Number dead(b) Number alive Observed Expected Observed Expected Low conductivity 20 (74) 14 (52) 13 (36) 19 (53) High conductivity 7 (26) 13 (48) 23 (64) 17 (47) Totals 27 (100) 27 (100) 36 (100) 36 (100) a [[Chi].sup.2] = 9.35; P = 0.0093 b Percentages of column totals in parentheses
We calculated the number of gosling deaths through day 15 per use-day at 9 locations (Table 5). We included in our calculations a small pool ("Green Pond") north of the refuge, fed by runoff from Harrison impoundment, that was unexpectedly and briefly used by one brood. We used all 19 broods that we monitored from hatching for this analysis. Of the three locations with the lowest number of deaths per use-day, 2 (Harrison and Pintail) had the highest specific conductivity of all locations used by broods. We also recorded deaths from broods 'in transit'. Eight goslings died or changed broods while in transit from one impoundment to another.
[TABULAR DATA FOR TABLE 5 OMITTED]
Only two broods used the three least saline locations, and only for a few days. The second most saline impoundment, N. Gadwall, was used for a total of only 3 d (12 use-days). On these days its specific conductivity ranged from 9500 to 9600 [[micro]seconds]/cm. We found no goslings under the age of 16 d on pools with water measuring more than 12,400 [[micro]seconds]/cm. This is well below the 18,000 [[micro]seconds]/cm that we found (Stolley et al., in press) caused 33% mortality in caged wild-strain goslings, and that Swanson et al. (1984) found caused 10% mortality in caged ducklings. However, lower levels of salinity cause sublethal effects (Swanson et al., 1984; Mitcham and Wobeser, 1988a, b) that could contribute to mortality.
The more saline locations at Fish Springs NWR were also the most open impoundments. Broods congregated on these, resulting in a higher number of adults that alertly scanned their surroundings, presumably for predators and other dangers. Because their view was unimpeded, adults were more likely to see a predator from farther away. Additionally, if broods were alarmed and scattered, goslings were less likely to be abandoned because there were more adults to follow. We often observed temporary brood mixing after broods had been startled off the dikes and into the water. In almost all cases goslings and their parents were reunited within a few minutes. Because salinity, levels were not high enough to cause direct mortality, the positive effects of grouping on large open pools appeared to more than compensate for any sublethal or longer term effects caused by the salinity. The great differences in number of deaths per use-day by location is not correlated with specific conductivity (Table 5). We speculate that broods using the less open impoundments, particularly those with shallow water such as Egret, experienced a higher level of predation by covotes which were ubiquitous at the refuge.
Human disturbance, such as that described by Sherwood (1966), may be a contributing factor in other locations such as N. Gadwall. All the impoundments are enclosed by raised dikes which are used by vehicles. At all locations we observed broods fleeing from approaching vehicles. In most instances broods ran from prime foraging and loafing areas on land into the water. However, sometimes a brood would scatter with several or all members running away from the water into mudflats or upland desert scrub. This made them extremely vulnerable to predation. Several instances of probable abandonment of slower goslings in poolside vegetation when broods were swimming away from vehicles were also noted. Avoidance of human disturbance may explain why the more heavily traveled but less saline southern impoundments of Avocet, Curlew and Mallard were rarely used by broods and even abandoned by the broods that hatched there.
The question of whether adult geese select against very saline locations to rear their broods warrants further investigation. In 1997, we saw no use of the most saline impoundment, Harrison, by broods younger than 16 d after 24 May, when the specific conductivity measured 12,400 [[micro]seconds]/cm. North Gadwall, the second most saline pool in 1997, was not used by goslings under the age of 16 d after 12 May, at which time specific conductivity measured 9500 [[micro]seconds]/cm. In 1996, specific conductivity ranged from 3300 to 11,600 [[micro]seconds]/cm in impoundments where broods under the age of 16 d were located. No broods of any age were on the most saline impoundments, Harrison and Gadwall, after 28 May and 27 May, respectively. At that time, specific conductivity levels were 10,100 and 14,000 [[micro]seconds]/cm, respectively.
The low fledging success rate experienced by goslings at Fish Springs NWR in 1997 was independent of salinity. In fact, at 2 of the 3 high conductivity locations, Harrison and Pintail, goslings experienced the least mortality of all locations. Harrison and Pintail appear to be preferred brood-rearing locations as illustrated by the high number of use-days. Six broods hatched on Harrison or Pintail; during the first 15 d following hatching only 1 of the 6 was observed away from these areas, and for only 3 d. These 6 broods were joined by 2 other young ([less than]15 d) broods. These broods may have benefitted from the unimpeded visibility at these pools and the alert behavior of numerous adults. During drought years we expect salinity levels on the refuge will be higher earlier in the year and may negatively impact gosling productivity.
Acknowledgments. - This project was funded by the U.S. Fish and Wildlife Service (USFWS) Contaminants Program. We thank B. Waddell, J. Banta and E. Gilbert for their help with this project. We are grateful for the help of B. Layland, R. Wright, K. Jenkins, J. Ontjes, M. Chabot-Halley, E. Bull Chief, D. Layland, F. Banta, J. Banta and M. Banta. We are indebted to K. Udy, P. Bemis, M. Pratt, M. Colson, S. Barras and M. Wilson for their assistance and advice. We greatly appreciate the expertise offered by M. K. Jackson and D. Coster. Many other individuals and organizations donated their time and skills to the project including T. Aldrich, S. Manes, R. Wilhelm, T. Neuman, D Stevens, J. Burruss and D. Anderson. We thank them. We gratefully acknowledge the Utah Chapter of the Wildlife Society for their provision of a scholarship grant, and a grant from the Utah Division of Wildlife Resources used to purchase telemetry equipment. Finally we appreciate the time and effort of two anonymous reviewers, whose incisive criticisms improved the ms.
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|Author:||Stolley, Dorie S.; Bissonette, John A.; Kadlec, John A.|
|Publication:||The American Midland Naturalist|
|Date:||Jul 1, 1999|
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