3.7 Territory Length Method (American Dipper)
Recommendations: The territory length method is recommended at the watershed level scale for relative abundance and estimating absolute abundance of breeding and, in some cases, wintering dippers (a territorial bird). This technique is best used during walking surveys. Works well on rivers with moderate or high densities of dippers.
Similar to the consecutive flush method for grassland passerines (Wiens 1969), this method involves walking along a river and flushing birds in one direction until they turn around, then flushing them in that direction until they turn around again. This method thus determines the upstream and downstream boundaries of the linear territories of dippers and kingfishers and can be used to estimate densities of territorial birds during the breeding season.
This method has been used successfully with kingfishers (Davis 1982), and dippers (Bakus 1959; Sunquist 1976; Vickery 1990). In British Columbia, however, it offers little benefit for purposes of kingfisher inventory because of the relatively low densities of kingfishers in the province compared to those found by Davis (1982). It may be most useful for estimating absolute abundance of dippers on streams with relatively high densities and where individuals have not been marked. This method is not feasible for harlequins.
Bakus (1959) and Price and Bock (1983) noted that dippers were not always consistent in turning at the edges of their territories. Price and Bock (1983) found that dipper territorial encounters were better indicators, and they chased birds from different directions to induce encounters. Dipper territories range from 400 m to 4 km (Kingery 1996). However, territories of isolated pairs were not easily determined and non-territorial floaters were not accounted for.
Dippers are also territorial on their wintering streams, but their territories are smaller and densities greater than during the breeding season, so this method may also be used in winter. For example, high counts on the Okanagan River included 35 dippers in 1 km or 13 dippers along 100 m of shoreline (Cannings et al. 1987). However, there is potential for confusion when flushed birds fly up and down stream.
Recommendations: Mark/recapture studies are recommended for all three riverine species if the objectives are to obtain data on absolute abundance, survival rates, demography, ecology, or behaviour of individuals. Recommended for kingfishers during the breeding season, and for dippers and harlequins for breeding and wintering populations. Mark/recapture is recommended at the local and management unit scales.
Mark-recapture methods have traditionally been used to help estimate population sizes, to determine migratory routes, to study individuals of breeding populations, and to determine individual fidelity to specific sites for many wildlife species (Verner 1985; Bibby et al. 1992). This technique has the inherent advantage of allowing population estimates with reasonable confidence limits without having to use expensive and time consumptive traditional census methods. Populations are estimated by using ratios of banded/unbanded birds and estimated annual mortality.
More recently, the estimation of survival rates for different age and sex classes has been feasible with a level of precision (Lebreton 1992). These data are crucial for management purposes, and can only be obtained from marked birds. For example, recent work by I. Goudie in British Columbia, has been linking breeding harlequins from streams in the Coast Range, southern interior, and Rocky Mountains with wintering sites in the Strait of Georgia.
In general, birds are captured in traps, then routinely aged, sexed, measured, and banded. Birds are marked using relatively permanent metal (usually aluminium) bands. Coloured tarsal bands, patagial tags, nasal saddles, and/or radio transmitters are also used to allow individual identification. Birds are "recaptured" by physically recapturing them, or by identifying them at a distance by their colour bands or other markers, or by detecting a radio signal. Statistical analyses are needed to process the data collected on "recaptures" in order to determine the probabilities of detection of a banded bird. These methods are now available through standard computer software. For discussions on statistics appropriate for mark-recapture studies consult Pollock et al. (1990) and Lebreton et al. (1992).
It is practical for harlequins, dippers, and kingfishers to be trapped and banded. During the past few years, there has been an extensive banding program for harlequins in the Pacific Northwest (I. Goudie pers. comm.). Alpha-numeric coded, colour tarsal bands have proven effective in allowing identification of individual harlequins at moulting and winter haulout sites and on breeding streams. Currently, there are a significant number of known-aged birds present on wintering and breeding areas and there are good opportunities for estimating survival rates and population trends. Regional wintering populations can now be estimated by comparing ratios of banded and unbanded harlequins at winter haul-out sites, especially where large numbers have been banded (e.g., Strait of Georgia).
It is practical to use mark/recapture techniques to inventory breeding populations at the watershed level, but is impractical at larger scales unless a massive banding effort is undertaken.
Little inventory or research has been conducted on dippers or kingfishers in British Columbia. Banding programs would be useful for surveys of breeding populations of both species, and wintering populations of dippers. Dippers do use traditional roost sites at night (Ormerod and Tyler 1990), and there is considerable potential for mark-recapture studies because they can be easily trapped and are a highly visible species. Dippers are usually banded with colour, alpha-numeric tarsal bands, as the legs of dippers are usually very visible to observers, especially when dippers perch on rocks or logs.
Kingfishers can be tempted to attack taxidermy mounts of kingfishers with playback calls during the breeding season (Davis 1980), which would facilitate capture in mist nets. Marking generally includes "painting" of wing feathers with various unique combinations of colour to identify individuals (Davis 1980). The legs of kingfishers are rarely visible, even when perched, so marking of the wings is the most appropriate technique.
Before conducting a mark/recapture survey ensure that mark/recapture data are necessary to meet the objectives of the inventory program, and justify the effort required to obtain necessary permits.