2.1 Special Inventory Considerations for Waterfowl and Allied Species

Within this manual, timing of surveys for waterfowl and allied species in BC is described in terms of the four stages of the lifecycle - breeding, moulting, migration and over-wintering. Different populations of birds in each species are inventoried during each of these stages. Many aspects of waterfowl biology and distribution influence the way in which they should be inventoried at each of these times.

2.1.1 Breeding

Wide Distributions and Low Densities

In general, populations of breeding waterfowl and allied species are widely distributed across the province, much of their habitat is inaccessible by road, and birds occur at low densities in remote areas. It is costly and time-consuming to inventory the entire breeding range. Therefore, breeding inventories concentrate on accessible areas with the highest densities of birds. These inventories can not be used to provide an unbiased estimate of population size for the entire province, but they are useful for estimating population size within clearly defined areas of specific habitat types.

Types of Breeding Surveys

Breeding waterfowl and allied species are commonly surveyed in three ways: (1) breeding pair counts, (2) nest counts, and (3) brood counts. In addition to being able to identify distinguishing characteristics of different age and sex classes, conducting these surveys requires knowledge about the behaviour, operational sex ratio, and nesting habits of each species being surveyed.

1. Breeding Pair Counts

• Territorial Behaviour: Breeding pair counts are based on the knowledge that established breeding pairs of dabbling ducks localize their activities to one or two ponds (Eng 1986). Thus, counting the number of breeding pairs on each pond repeatedly over the breeding period (from pair bonding until the female is well into incubation) is a valid way to estimate the size of breeding populations. Breeding pair counts are less valid for species that move around in large home ranges (e.g., Canvasbacks, Redheads, Green-winged Teal) during the breeding season. Movements may cause birds to be counted twice and thereby lead to overestimates of the population size.
• Timing of Counts: Ideally, pairs are counted after migrants have departed, but before males desert their incubating females. Counts of multiple species should be timed to include the pre-nesting, laying and early incubation stages of the species of interest. This may extend over a period of at least 20 to 30 days to include early- and late-nesting ducks. Dzubin (1969) proposed that lone males, grouped males and males in aerial flights should be included as pairs before a certain date. After that date, grouped males are more likely to be post-breeding males from another location. Different cut-off dates have been established for early nesters (Northern Pintails and Mallards), intermediates (wigeons and Northern Shovelers) and late nesters (Blue-winged Teal and Gadwalls).
• Operational Sex Ratio: The "indicated breeding population" is based on the operational sex ratio of the species (Dzubin 1969). For example, only half the grouped males are considered pairs in species known to have 2:1 sex ratios (e.g., Hooded Mergansers, Lesser Scaup). Sugden and Butler (1980) recommend that lone male and pair counts provide the best index to breeding populations for Canvasbacks and total female counts provide the best index for Redheads. Recommendations for counting "indicated pairs" of other duck species await further study. Breeding geese, swans and cranes remain paired throughout the nesting season which extends the time available to survey breeding populations. Lone males indicate pairs only during incubation and males in groups are never considered pairs (Eng 1986).
• Recording Breeding Pair Counts: Record the number of pairs, lone males, and males in groups noting the number of males in each separate group.
• Pairs - The number of pairs presumed to be breeding pairs. Pairs are usually seen close to shore and may exhibit pair-bonding behaviour such as display, courtship, etc.
• Lone males - The number of resident males that may be defending a territory. These males will commonly be seen repelling conspecific males.
• Lone females - The number of females feeding intensively between incubation periods. These females are usually seen late in the season.
• Males in groups - The number of males in an isolated group. For Mallards, these are post-breeding drakes and each individual indicates a breeding pair. These groups are seen late in the season after incubation begins.
• Mix flock (sex ratios in a mixed flock) - It can be useful to record the number of females and males present where mixed flocks of both sexes are present. This situation is most often seen early in the season.
• Isolated pair - The number of pairs observed to be isolated from other waterfowl. This is only useful for Goldeneye and Bufflehead. Isolated pairs are usually found near the shoreline and will strongly defend their territory.
• Immature group - The number of immature males and females observed. This is only useful for some diving duck species such as Barrow's Goldeneye, Buffleheads, etc.

2. Nest Counts

• Nesting Habitat: Although it is time-consuming, counting nests can provide estimates of the size of a breeding population in a defined area of habitat. Habitats must be searched thoroughly to find nests that are usually hidden in vegetation. Waterfowl nests in open upland habitat can be found more easily by dragging a cable chain (Higgins et al. 1969). Nests near water require searches on foot in chest waders, by canoe or by kayak.
• Timing of Counts: Nests are counted by systematically covering nesting areas at specified time intervals to locate early and late nesting birds. Nest searches in dense cover should be conducted while females are still incubating so that flushing females will indicate a nest's location. Not all pairs initiate laying at the same time and some nests may be destroyed between search periods. Consequently, not all nests are found, while renesting attempts may result in some duplication. Total counts usually represent minimum estimates.

3. Brood Counts

• Index of Annual Waterfowl Production: Brood counts provide an index of annual waterfowl production, possibly a measure of breeding success, and possibly an index of breeding population size. Gillespie and Wetmore (1974) also suggest that brood surveys provide a better index of an area's capability to support waterfowl than do pair counts. However, the high vulnerability of broods to adverse weather conditions and predation (Breault pers. comm.) reduces the accuracy of brood counts as estimates of either annual breeding population size or habitat capability. Brood surveys provide an index of annual waterfowl production, although multi-year surveys may help answer the question of habitat capability. Brood counts can also provide a measure of annual breeding success if conducted in conjunction with breeding pair or nest counts.
• Timing of Counts: There is greater flexibility in the timing of brood surveys because birds are sedentary longer than during spring pair counts (Gillespie and Wetmore 1974). Brood counts should occur after hatching but before fledging. Many species in this inventory group are asynchronous breeders, and each species has its own chronology (refer to Table 1); therefore, the timing and duration of inventories will vary depending on which species are being inventoried.
• Brood Behaviour and Movements: Broods are usually more secretive than adults and by the time most broods have hatched, the emergent vegetation is lush and visibility is reduced. Repeated surveys are recommended to increase opportunities for brood detection. However, broods of most waterfowl species move from pond to pond, increasing the likelihood of double counting. Therefore, in repeated surveys, appropriate analytical methods must be used to avoid overestimating population size.
• Brood Identification: Gollop and Marshall (1954) recommend that the age of each brood be recorded for waterfowl species so that they can be re-identified on subsequent counts. Ageing the young of asynchronous hatchers, e.g., coots and grebes, is imprecise because young of the same age are usually different sizes. The problem is exacerbated by the fact that some young are preferentially fed. Similarities between the female plumage of different species of waterfowl (e.g., Red-breasted Mergansers resemble Common Mergansers) make it difficult to identify older broods.