Loss of Feeding Time
Flushing often reduces the time waterfowl spend feeding by forcing them to change their food habits, feed at night, or leave prime feeding grounds (Hamann et al. 1999). Several studies on a variety of species have documented this loss of feeding time due to disturbance from motorized watercraft. Kaiser and Fritzell (1984) studied the behavior of green-backed herons in relation to the level of recreation on Missouri's Ozark Scenic Riverways. When the number of recreationists on the river increased, the herons often left for areas of dense habitat or less productive tributaries (Kaiser and Fritzell 1984). Kahl (1991) found that disturbance at Wisconsin's Lake Polygan resulted in 48-53% less daylight feeding time for canvasbacks. Galicia and Baldassarre (1997) studied the effects of tourboats on American flamingos in Yucatan, Mexico and discovered that the average 13 disturbances per day resulted in a daily loss of 13% in feeding time per individual per day. They also observed that on days when tourboat use was exceptionally heavy, feeding may have been totally prohibited (Galicia and Baldassarre 1997).
Knapton et al. (2000) found that because of disturbance, canvasbacks, redheads, and scaup leave the inner bay of Long Point Bay, Lake Erie during the day to feed in less productive areas. Tuite et al. (1983) observed that many wintering waterfowl were driven from their preferred feeding zones by powerboats and other disturbances in lakes in south Wales. During the highest level of activity at these sites, mallard, mute swan, wigeon, and pochard flocks were kept out of favored feeding locations completely (Tuite et al. 1983).
Energy Loss
Flushing increases the energy expenditure of waterfowl, which can be detrimental for migration and reproduction. The energy cost of flight is high, 12 times the basic metabolic rate of waterfowl (Ward and Andrews 1993). Therefore, waterfowl must increase their food intake to make up for the lost energy, which can be difficult when food supplies are limited (Ward and Andrews 1993). For example, during 287 hours of observation, BTlanger and BTdard (1990) found that disturbed snow geese spent an average of 55.9 seconds in flight per disturbance. They estimated the average disturbance rate caused a 5.3% increase in hourly energy expenditure due to flight alone (BTlanger and BTdard 1990).
Significant energy loss can be particularly harmful to incubating waterfowl. For example, common eiders do not eat for 25 days during incubation, relying on stored body reserves, to improve the success of their eggs. During this time, they lose 40% of their body weight (Gabrielson and Smith 1995). By rarely leaving the nest, they use little energy, losing only 20-25 grams of body weight per day. If they are flushed by disturbance, this routine is interrupted, and they must leave their nest to obtain additional energy (Gabrielson and Smith 1995).
Impact on Breeding Success and Survival of Chicks
Disturbance from motorized watercraft has also been shown to negatively impact the breeding success of waterfowl and the success of their eggs and chicks. Galicia and Baldassarre (1997) observed that disturbance from motorized tourboats reduced the courtship of flamingos from 23% to 7%. Bouffard (1982) also found that uncontrolled boating within 300 yards of a prime nesting area in Nevada's Ruby Lake National Wildlife Refuge caused courting ducks to flush. Boating can directly impact egg survival: in Montana, water skiers and powerboats have run over white-winged scoter hens and broods (Hamann et al. 1999). Motorboats have been found to tip over waterfowl nests near reeds or free-floating grebe nests (Reichholf 1976), or to swamp nests when going at high speeds (Ward and Andrews 1993). Disturbance from motorized boats can negatively impact egg survival indirectly, as well, by flushing incubating adults. For example, Bouffard (1982) found that when boats came within 300 yards of diving ducks, female ducks took flight, leaving their eggs exposed to chill or overheat.
Young waterfowl are also at risk of starvation and predation following disturbance. Boats can increase predation on nestlings and/or nestling starvation by separating broods. At the Archipelgo of Turko (Finland), Mikola et al. (1994) observed that when boats came within 30 meters of velvet scoter broods, the females left their ducklings and swam toward the boat. Gulls used this opportunity to prey upon the abandoned ducklings - the attack rate of gulls was 15 times greater after a disturbance than when broods were undisturbed (Mikola et al. 1994). ,hlund and G"tmark (1989) experimentally disturbed 113 broods of eider ducklings in Sweden and found that disturbance significantly increased gull encounters with ducklings. The total gull encounters and successful attacks were greater than 200 times higher on disturbed broods (,hlund and G"tmark 1989).
Comparison of Disturbance Based on Watercraft Type
Because watercraft vary in size, sound, speed, and use, the level of disturbance to waterfowl varies considerably based on watercraft type. For example, a study by Havera et al. (1992) showed waterfowl took flight in response to hunting and fishing craft, while few flushed because of barges. In addition, birds flushed farther in response to hunting and fishing boats than to barges (Havera et al. 1992). On Long Point Bay, Lake Erie, the primary cause of disturbance in the spring was commercial fishing boats, while hunting boats were the primary form of disturbance in autumn (Knapton et al. 2000). Korschgen et al. (1985) found that birds were more sensitive to boats with outboard motors.
The effect of personal watercraft (PWC) on waterfowl is a major concern because of their ability to operate at high speed in shallow areas, such as wetlands and near shorelines, where waterfowl feed and breed. Additionally, PWC may cause more disturbance to waterfowl than other boats because they produce a large vertical and horizontal spray due to their deep-V hull (Rodgers and Schwikert 2002). Rodgers and Schwikert (2002) studied 23 species of waterfowl on the east and west coasts of Florida and observed that the great blue heron flushed farther when approached by PWC than by boat, while anhinga, little blue heron, willet, and osprey exhibited significantly larger flush distances in response to the outboard powered boat (Rodgers and Schwikert 2002). Further studies on the impacts of PWC on waterfowl are needed.
Conclusions and Possible Management Solutions
The noise, speed, and proximity of boats influence their impacts on waterfowl. Researchers, therefore, have offered a number of methods to reduce disturbance, including the following:
- Reducing speed limits for boats and PWC
- Establishing buffer zones
- Establishing refuges (year-round or seasonal)
- Designating no-wake zone
- Educating the public
The best way to protect waterfowl varies by site, species, and time of year (Korschgen et al. 1993, Bratton 1990, Rodgers and Smith, 1995). However, Mori et al. (2001) found species composition, activity, and flock size also to be significant factors in the amount of disturbance to certain species. According to Rodgers and Schwikert (2002), when dealing with mixed species, buffer zones should be based on the largest flush distance or the species most sensitive to human disturbance. It would be ideal to conduct studies on individual waterbodies to establish management needs. However, if the time and money needed is not available, managers should take a precautionary approach and choose a refuge or a large buffer zone, which are most likely to reduce the impact of watercraft on waterfowl.
Regardless of which management option is selected for a given water source, public education should be included to improve compliance and overcome public disapproval. Any management option to reduce the impact of motorized watercraft on waterfowl is more likely to be successful if boaters understand the purpose behind restrictions and the consequences of violations.
-- Kate Cywinski is a graduate student in Environmental Studies at the University of Montana.
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