Survey Methods | How Many? | Aerial Surveys: Disadvantages

A map of Africa that shows the aerial survey area for the Zambezi Valley in north Zimbabwe with layers that can be selected to show the area of the Strata, Blocks, Transects, and Flight Paths.

The Strata map layer shows a large survey area on the left and a smaller one below it to the right. The larger survey area is divided into 24 different irregularly shaped strata. The smaller survey area is divided into three different irregularly shaped strata.

The Blocks map layer shows a roughly circular area of irregularly shaped and spaced blocks on the left-hand side. From there, a scattering of blocks appears going diagonally to the upper right and diagonally to the lower left. A separate cluster of six blocks appears on the right-hand side of the map.

The Transects map layer shows a roughly triangular area on the left-hand side of the map with closely spaced horizontal lines. To the right of it is a roughly trapezoidal area with vertical lines that are even more closely spaced than those in the area to the left. These closely spaced vertical lines continue in a roughly finger-shaped area extending to the right from the top of the trapezoid. Below this area is an area with closely spaced horizontal lines at the top with three more widely spaced lines in the middle and more closely spaced lines below it. Areas with increasingly widely spaced horizontal lines extend beyond it to the right-hand side of the map. Above this area of horizontal lines is an area with widely spaced vertical lines. Above this area of vertical lines is an area of widely spaced horizontal lines.

The Flight Paths map layer shows a roughly triangular area on the left-hand side of the map with closely spaced horizontal lines. To the right of it is a roughly trapezoidal area with vertical lines that are even more closely spaced than those in the area to the left. These closely spaced vertical lines continue in a roughly finger-shaped area extending to the right from the top of the trapezoid. Below this area is an area with closely spaced horizontal lines at the top with three more widely spaced lines in the middle and more closely spaced lines below it. Areas with increasingly widely spaced horizontal lines extend beyond it to the right-hand side of the map. Above this area of horizontal lines is an area with widely spaced vertical lines. Above this area of vertical lines is an area of even more widely spaced horizontal lines. Clustered areas with higher concentrations of intersecting lines appear on the lower left-hand side of the map extending diagonally to the top right and horizontally to the right. A separate area with clusters of higher concentrations of intersecting lines appears at the lower right.

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Aerial Surveys

Aerial surveys are most effective on relatively flat ground with sparse vegetation. They cannot be used to survey forest elephants, which are difficult to see from the air. Aerial surveys require significant resources including an airplane and specialized equipment, as well as a pilot and experienced observers.

Sample counts assume that the count performed in the sampling area can be extrapolated to the entire survey area. Nonuniform elephant distributions can lead to undercounting or overcounting, depending on the herd distribution at the time of the survey. Undercounting can also occur when calves hide under an adult's belly or in the center of the herd. Overcounting can occur when elephants that have already been counted move to an uncounted transect and are counted again. Total counts can be more accurate but are too expensive and time-consuming to undertake in a large survey area.

Population estimates based on aerial surveys can be imprecise due to variations in the landscape and elephant distribution, and human sampling error. However, researchers can reduce errors by selecting the appropriate type of aerial survey for the landscape and elephant distribution, by keeping flight speed and height consistent, and by double-checking observers' identifications.

The map shows the survey area for the Zambezi Valley in Zimbabwe, with transect sample counts in strata with flat terrain and block sample counts in strata with hilly terrain. The total count method was not used in this survey area.

Suggestions for viewing the map:

Select the flight paths layer to see the actual path that the airplane flew during the survey. To best view the block and transect layers, unselect the flight paths layer.