4. HOW TO DETERMINE BREEDING STATUS OF RIVERINE BIRDS
Data on breeding populations can be collected either indirectly (behaviour of adults) or directly (nests, eggs, or young).
Harlequins form pairs on winter grounds and arrive in spring on the nesting rivers. All pairs detected should be considered to be potential breeding pairs. Harlequin populations have a sex ratio significantly skewed to males. Unpaired males are often present in proximity to pairs. Nests can be found by watching from a blind as females go to the nest to lay eggs, by systematic searches of river banks, tree cavities, and canyons, by using pointing hunting dogs to detect incubating females, or by radio-telemetry tracking of females. However, nests are very difficult to find and generally should not be searched for because of the danger of abandonment and the very high cost/benefit ratio related to inventory.
Broods are reasonably visible after they leave the nest. Brood counts are useful in estimating populations but significant proportions of pairs defer breeding in any given year (e.g., mean = 0.44 in Iceland, Bengtson 1972). In some years young survival during the first week is very poor, so broods may not be found if surveys occur after mortalities. Females are not known to renest (Goudie et al. 1994a).
Dipper nests can be found, but many may be in inaccessible places. Searches for nests should be concentrated along canyon walls, rock bluffs, bridges, log jams, boulder piles, and high cut gravel banks of nesting streams. Nests are most easily found during the construction phase (late March through mid April depending on region) and when parents are feeding young in the nest. Watch for birds flying back and forth and follow them to their origin. Observers may need to hide when close to the nest because dippers can be wary of going to the nest when being observed.
Kingfishers nest in excavated cavities in river banks or lake banks, where they burrow into soft sedimentary material. Nest burrows are usually easily spotted but, at times, the entrance hole may be partially obscured by overhanging roots or located a considerable distance from water. Active burrows are best identified by the presence of adults and the presence of fresh markings around the entrance hole: the shuffling feet of the kingfisher leaves a distinctive set of two grooves along the bottom of the burrow. Unused or old burrows will likely have had the grooves sloughed away by rain or wind. Kingfisher entrance holes are several times larger than bank-nesting swallow burrows, but natural holes may be confusing at times. Some burrows are used for roosting. Although one or more burrows may be present in a territory, only one will be used for nesting in a given year.