Birds are usually captured so that they can be banded and/or marked, and to gather information on physiological condition and morphometrics. Banded birds then allow biologists to gather more detailed information on population sizes and demographics than is possible with other methods. Capturing of birds for inventory purposes must be carefully rationalized, as capture can be stressful or injurious to individual birds and the value of marking individuals should be high.
Special banding permits must be obtained from federal (Canadian Wildlife Service) and/or provincial (Ministry of Environment, Lands and Parks) agencies, and workplans must undergo a peer and veterinary review or obtain the approval of an animal care committee. It is very important that efforts to explain capture activities to the public are made to reduce negative reaction. It is equally important to obtain permission to enter private property, ecological reserves, and other restricted areas.
Capture of harlequins must be supervised by trained professional biologists who have been issued capture and banding permits from the Canadian Wildlife Service (CWS). Harlequins use traditional sites for moulting and can be most easily trapped at this time in late summer when they are flightless. Birds are best captured by drive-trapping: several kayaks and a motor-driven canoe (6 boats are ideal) "drive" swimming birds into a double-winged drive trap with one-way access (Figure 2). This method has been used to trap hundreds of birds in the Strait of Georgia (I. Goudie pers. comm.).
Important points to consider include: proximity to access for boat launching, local weather conditions and exposure, strength of tidal currents, shoreline topography, wave action, other human disturbance factors, and safety for trapped birds.
Mortality of trapped birds must be minimized. This can be best accomplished by watching for birds getting caught in a net and possibly drowning and trapping only as many birds as can be handled promptly by the crew. Avoid trapping during adverse conditions. Capture mortality for harlequins is <1% in the Strait of Georgia (I. Goudie pers. comm.).
Figure 2. Possible position for a drive trap to capture harlequin ducks at sea.
Riverine birds can be trapped on nesting streams by stringing mist nets across streams or shorelines. Note that an additional permit from Canadian Wildlife Service is required for mist-netting birds. This method is most feasible on smaller streams, or larger streams that are shallow and not too turbulent, because birds must be immediately retrieved from nets to avoid drowning. Dippers and kingfishers can be captured with nets with 40-50 mm mesh. Larger (100 mm); heavier gauge mesh is required for harlequins, but will also catch the other species.
For harlequins, mist-netting must occur before males abandon their mates and return to the coast (after incubation begins). Harlequins are not easily trapped when swimming, although they can be flushed into traps, so traps should be set where birds are most likely to be flying. Mist nets should be set-up downstream of observed birds. Ideally, a passive setup is best which intercepts birds as they ascend the watershed in spring. Localized hen and brood captures is possible in late summer.
For dippers, nets can be strung perpendicular to the shorelines that they use for foraging, or on their approach routes to their nest sites. Dippers can also be captured at night at roost sites. There, when using a flashlight, they can be picked up by hand (Ormerod and Tyler 1990). Although they do not often roost communally, this method is an alternative to netting, especially where they roost under bridges. Young dippers in nests should not be handled because of their tendency to abandon the nest prematurely when disturbed (Price and Bock 1983). Young dippers can be captured in mist nets after they fledge.
For kingfishers, mist nets can be strung perpendicular to shorelines where they tend to fly, near hunting perches, or on approaches to their nesting burrows. Several traps have been designed to capture cavity-nesting birds like woodpeckers and swallows and some of those traps can be used to capture kingfishers at their burrows (Rendell et al. 1990; Jackson and Parris 1991). For a review of mist-netting techniques see Keyes and Grue (1982) and Bleitz (no date, distributed by Avinet, Inc.).
