3.3 Aerial Surveys

Recommended Use: This method is used at all 3 levels of inventory intensity depending on species and season. See Table 2 for species-specific recommendations.

Presence/Not detected

Aerial surveys provide an excellent means for detecting conspicuous birds. Species that are large, or occur in large flocks are appropriate targets for this method. Aerial surveys are particularly effective for determining the presence/ absence of:

• American White Pelicans in foraging areas;
• Great Blue Herons foraging on tidal flats, lakeshores and open fields;
• Western Grebe wintering or staging concentrations on lakes and at sea; and
• concentrations of nesting Red-necked and Eared grebes.

Relative Abundance

Data from aerial surveys can be effectively used to produce relative abundance indices for comparing waterbird populations temporally and geographically, especially for nonbreeding populations of Western Grebes and breeding and nonbreeding populations of Great Blue Herons along the British Columbia coast.

Absolute Abundance

For locations where the entire study area is exposed, estimates of total numbers of birds can be made. This is applicable to Great Blue Herons on tidal flats from spring through autumn, American White Pelicans on breeding and foraging lakes in spring and summer, and wintering concentrations of Western Grebes.

Aerial surveys have been used since the late 1940's to census wildlife populations (Caughley 1979). Waterbirds (mainly waterfowl) are regularly surveyed by fixed-wing aircraft in British Columbia, and this method is the most effective technique for acquiring data on waterbirds over large geographic areas, or where the birds are difficult to census by other methods due to problems such as ground access restrictions, heat haze, or angle of observation (e.g., Savard 1982, 1985; Butler et al. 1986; Butler and Campbell 1987; Butler 1989). Since counts are relatively instantaneous, biases caused by movement of birds between areas may be avoided.

Surveys are usually conducted using high-wing single or twin engine fixed-wing aircraft. Helicopters are not suitable, because of the high degree of disturbance caused by low-level flights. Flight altitudes usually range from 25-100 m above ground level at airspeeds that are as slow as feasible (110-240 km/hr) (e.g., Morrison et al. 1989).

Video cameras and aerial photography are sometimes used in conjunction with aerial surveys. Aerial photography can be used to obtain accurate estimates of flocks in limited areas, as well as provide valuable information about the habitat. Photographs can also be used to improve estimates made during flights and as training for estimation of numbers in flocks.

Factors to consider in the use of aerial surveys

Sources of Bias

• Savard (1982) and Pollock and Kendall (1987) cautioned against use of aerial surveys because of the difficulty in observing cryptic species (i.e., small grebes) and other observability biases such as the difficulty in identifying birds viewed at oblique angles, observer fatigue, missing birds that dive, and weather factors. Because of these biases, aerial surveys can often underestimate populations, compared to ground-based surveys, because birds are more often missed (Pollock and Kendall 1987).
• Bird behaviour and detectability will vary with weather, as will the ability of observers to detect birds under different conditions. It is generally recommended that surveys should not be conducted during periods of heavy rain, fog, snow, strong winds, or extreme temperatures. For example, grebes are difficult to count on water when winds create waves or swells.
• Other important sources of bias include:
• birds may flush (B-AWPE, B-GBHE) or dive (grebes) ahead of aircraft, which may reduce the accuracy of counts;
• variables such as light conditions, different observers, altitude flown, and precise route flown are difficult to control; and
• observer fatigue is inevitable in all but the shortest of surveys, affecting consistency of results.
• Briggs et al. (1985a) compared aerial surveys with ship surveys and found that aerial surveys recorded higher densities of waterbirds, but had lower rates of species-specific identification (77-96% vs 95-97%). Therefore, although total birds were more accurately estimated, identification of those birds was more difficult. Grebes are the only species in this inventory group that might be confused with other species during aerial surveys.
• Data from aerial surveys can be improved by ground-truthing subsets of the survey area and correcting for differences. Ground-based counts are presumed to be more accurate than aerial counts, because there is more time to observe birds at specific locations and repeat counts can be made. For Western Grebes and Great Blue Herons, count concentrations from land at the same time as aerial surveys are done.
• Aerial surveys of Red-necked and Eared Grebes on the coast during nonbreeding seasons are not feasible because of probable confusion with other waterbirds. Western Grebes in winter, American White Pelicans, and Great Blue Herons in open foraging habitats are distinctive and easily viewed from the air. It is not feasible to survey breeding colonies, for any of these species, for numbers of active nests. Surveys for breeding pairs of grebes are feasible, although confusion with ducks will cause biases.

Logistics and Cost

• Large areas can be effectively covered in a short period of time. Remote areas can be easily accessed, especially if surveys have to be repeated at regular intervals. Few trained personnel are required which greatly reduces inter-observer variability and improves the comparability of counts. Procedures can be more easily standardized between study areas and between years if fewer personnel are involved.
• Although aerial surveys appear relatively costly, they are usually the most cost effective method for censusing large and remote geographic areas. However, aerial surveys designed solely to count species included in this manual would not be a wise use of funds. Censusing all available birds in the survey area is more cost-effective.
• One additional factor to consider is that aerial surveys are probably relatively dangerous for personnel, compared to ground surveys.

Office Procedures

• Review the section, Conducting a Wildlife Inventory, in the introductory manual Species Inventory Fundamentals (No. 1).
• Obtain any necessary permissions for over flying survey areas (e.g., restricted airspace near airports or military bases (contact Airport Operations); Ecological Reserves (contact local Ministry of Environment office). Contact landowners, for reasons of courtesy, if privately-owned wetlands are going to be overflown at low altitude.
• Select areas to be surveyed from 1:20 000 or 1:50 000 maps, making use of existing data, and experience with the study area.
• Obtain 1:50 000 air photo maps and plan flight lines according to available habitat. Plan survey route to minimize travel time between beginning and end points.
• Determine Biogeoclimatic zones and subzones, Ecoregion, Ecosection, and Broad Ecosystem Units for census areas from maps.
• Choose the appropriate flying altitude. Fly for American White Pelicans at about 500 m, for Great Blue Herons at about 50-100 m, and for grebes between 30-60 m.

Sampling Design

• Stratify habitat based on expected densities (low, medium, high) for the species under study.
• For large-scale studies, randomly select sample blocks from the three strata. For intensive studies of smaller areas, fly the entire area. Note: if the whole area within a stratum is being flown, label the stratum as one sample block.
• Survey lines (transects) should be flown to cover all habitat where birds are expected within predefined survey areas. Transect lines can be straight lines across broad expanses of water/mudflats/fields, or can follow contours of coastlines, lakeshores, or rivers. Count birds along survey lines from both sides of the aircraft out to a predetermined distance (25-200 m); include all available habitat by conducting several passes, while ensuring that areas are not counted twice. Narrower transect strips generally allow greater observation accuracy than broader strips (Briggs et al. 1985b), but narrow transects may increase biases when counting grebes because birds at close detection distance may dive more readily.
• When surveying wetlands, small lakes, or discretely bounded marine waters the entire body of water can be surveyed, even if several passes are required. This method provides estimates of total numbers per wetland. Survey bird concentrations by circling around several times and making several estimates.

Sampling Effort

• Approximately 600-1,000 kms of transects can be flown per day.
• Surveys should be repeated several times during the breeding or wintering season.
• Western Grebes - Annual monitoring is recommended for breeding and wintering populations.
• Red-necked/Eared Grebes - Major colonies should be surveyed every 3-5 years.
• American White Pelican - Annual monitoring is recommended.
• Great Blue Heron- Annual monitoring is recommended.

Sampling Standards

Time of day

• To avoid low sun angles and glare during spring, summer, and fall, schedule surveys on clear or overcast days, between three hours after dawn and three hours before dusk.
• Survey times along the coast should also take into account tidal cycles. Plan timing of coastal surveys to coincide with low to mid tide levels (B-GBHE) or between 1030-1400 hours (wintering B-WEGR)

Weather

• Surveys should not be conducted in winds greater than 30 km/hr, or during periods of rain or fog. On sunny days, orient flight paths to avoid glare.
• A certain amount of flexibility has to be planned into scheduling to accommodate delays caused by bad weather or mechanical problems.

Personnel

• To avoid observer fatigue, which will bias the accuracy of data collected, total daily air time should not exceed 6 hours. Each session should last no more than 2 to 3 hours with half hour breaks.
• Personal comfort note: Toilet facilities are not available in-flight. The survey team should restrict beverage intake, especially those with caffeine, during the hour prior to take off. However, during the flight, energy snacks (chocolate bars, fruit, etc.) are recommended to reduce spotter fatigue.

Personnel

• A pilot with previous aerial survey experience is preferred.
• In addition to the pilot, it is recommended that the crew should consist of a navigator, in the co-pilot seat, and two spotters in the left- and right-hand-side passenger seats.
• The survey crew members need to be trained in standard methods of flock size estimation and identification.
• Consistent biases in estimation can be improved with training. Spotters should practice making estimations of flock sizes and species composition from aerial photographs and video tapes. With discussion between the observers, this procedure can greatly reduce the error factor of inter-observer variability.
• Members of the survey crew must know exactly the specific data that they are responsible for collecting (see data forms). This will avoid oversights and duplication. Each crew member should be familiar with the flight route and be responsible for all the equipment that they will be using during the flight.
• All personnel must have a high tolerance for motions associated with flying. Gravol or other preventative medications should be taken prior to take-off if there is the slightest chance of motion sickness.

Equipment

• Overhead fixed-winged aircraft are recommended (e.g., Cessna 182 or 206; Beaver). The same type of aircraft should be used throughout a survey to standardize noise disturbance and speed.
• It is recommended that the aircraft be fitted with bubble windows to allow for better spotter visibility.
• The navigator should be equipped with a chronometer, Global Positioning System (usually available with the aircraft), detailed maps of routes, pencils to trace flight route, precision watch for noting time, and a tape recorder to record data.
• Each counter should have 7-10X binoculars, a tape recorder, extra blank tapes, maps of routes, a precision watch, extra batteries, and pencils and field note book in case of tape recorder failure.
• Video and/or still cameras may also be used to supplement the data. Again, carry spare film and batteries on board.