3.5.5 Airphoto technique

See Table 3 for species-specific recommendations. Absolute Abundance can be obtained for concentrated non-breeding flocks of large bird species that contrast with their background (swans and Snow Geese).

Photographs of flocks of large conspicuous birds are taken from an airplane above ground and then birds in the photo are counted later. This technique is suitable for obtaining an accurate absolute abundance estimate of numbers and sometimes age ratios of large conspicuous birds concentrated in a defined area (e.g., Snow Geese, Boyd pers. comm., swans, Sandhill Cranes).

Advantages:

• Provides accurate counts of large flocks concentrated in an area that are difficult to estimate by sight from the air or ground.

Disadvantages:

• Takes more time than counts from the air e.g., two days to count photos of snow geese in flocks of 40,000; more time if flock sizes are larger (Boyd, pers. comm.).

Office Procedures

• Review the introductory manual No. 1 Species Inventory Fundamentals.
• Obtain relevant maps of the project area (e.g., 1:50 000 air photo maps, 1:20 000 forest cover maps, 1:20 000 TRIM maps, 1:50 000 NTS topographic maps). Any map which is used to record data should be referenced to NAD83.
• Outline the Project Area on a map and determine Biogeoclimatic zones and subzones, Ecoregion, Ecosection, and Broad Ecosystem Units for the Project Area from maps.
• Delineate the Project Area on topographic maps or air photos.

Sampling Design

• For Absolute Abundance surveys, both the area of the wetland sampled and the Study Area size must be known. Note that these surveys can only be considered estimates of total abundance if all biases have been eliminated. Biases that can not be eliminated should be measured (usually with more survey effort) and used to correct counts.
• Total counts of defined areas, or if photos are extensive, a suitable probability sample of photographs, or defined areas within the photographs.

Sampling Effort

• The time it takes to photograph flock(s) in an area(s), plus processing time for counting flocks.

Personnel

• A pilot with previous aerial survey experience in the study area.
• One highly trained and experienced observer with experience in taking photographs from the plane.

Equipment

• 35 mm SLR auto-wind camera equipped with a 30-110 mm zoom lens
• 35 mm SLR auto-wind camera equipped with a 300 mm lens
• 1600 ASA colour print or slide film for overcast days
• 400 ASA colour print or slide film for sunny days
• Dissecting microscope (12x power)
• Modified pen (a pin attached to a microswitch/digital tallier) for use with print film
• Hand tally counter for use with slide film
• Projection equipment, a large sheet of paper to attach to the wall, and a fine-tipped felt pen for use with slide film
• Air photos of the study area
• Topographic maps of the study area
• Coloured grease pencils and lead pencils

Field Procedures

• Weather:
• Do not survey in winds greater than 25 km/h, in rain or fog.
• Overcast days are best for discriminating between white and grey birds (adult and young geese/swans).
• Fly at speeds of 130-170 km/h depending on the fixed wing aircraft
• Fly at an altitude of 400 m to minimize disturbance to the birds.
• Upon locating a flock, manoeuvre the airplane to within 200 m and bank for the photo sets. This altitude will ensure good coverage of large flocks, good photo resolution and little interference from clouds.
• Shutter speed should be a minimum of 1/500 s to overcome movement from the airplane vibration (especially given the long lens).
• Take enough photos to cover the entire flocks with 25-50% overlap between photos - only a few photos are needed for small flocks (<500 birds) but > 30 photos are needed for large flocks (>20,000 birds).
• Do not photograph birds in flight because photo-delineation will be more difficult and there will be an increased chance of missing birds and double counting birds.
• If the flock moves prior to or during the photo set, fly > 2 km away, wait for the birds to settle, and then gradually spiral inwards.
• Take flock photos with the 110 mm lens to produce photo scales of between 1:4,000 and 1:6,000.
• Take overview photos with the 30 mm lens to help locate and delineate each flock.
• Take photos with a 300 mm lens randomly throughout the flock to obtain pictures used to estimate age ratios.
• All photos should be automatically inscribed with a number using the camera data back.
• Record flock numbers and their corresponding photo numbers onto maps of the study area along with the exact route flown.

Data Entry

The Design Components for this survey are blocks (polygons = Study Area). When digitally entering your survey data, choose `Block' from the `Design Component Type' picklist.

Data Analysis

• Counting - print film method (preferred method):
• Print film on 10.2 cm x 15.2 cm paper at three times normal contrast to help discriminate between grey birds (young) and background features.
• For overlapping photos, identify common points on adjacent prints and draw lines around the geese to be counted.
• Entire photos or portions of photos can be used as sample units for age ratios.
• Count birds in photo under a dissecting microscope (12x power).
• Punch holes through each goose image with a modified pen (a pin attached to a microswitch/digital tallier) to avoid duplication.
• Counting - slide film method:
• Project slide onto a large sheet of paper taped to a smooth wall
• Register the image on the paper to enable realignment
• For overlapping photos, identify common points on adjacent slides and draw lines around the geese to be counted.
• Entire photos or portions of photos can be used as sample units for age ratios.
• Count birds in photo from projected image
• Mark each counted bird with a fine-tipped felt pen to avoid duplication, and count with a hand tally counter
• Density estimates may be calculated by dividing the number of birds observed by the area photographed if a complete count on the photographs is done. If a sample of photos is counted, or a sample of areas within photos is counted, then appropriate estimates will need to be used based on the method of sampling. These can be extrapolated to estimates of total abundance if the entire population or a known proportion of the population was photographed.