The second largest concentration of common terns (Sterna hirundo) in North America is found on Tern Islands, a set of three small barrier islands separated by water at high tide located within Kouchibouguac National Park. These seabirds are indicators for the condition of coastal, marine, as well as estuarine ecosystems due to the use of these nesting and/or breeding grounds, and their reliance on the distribution of small fish populations in lagoons or along the outer beaches of barrier islands throughout the breeding season. The purpose of the common tern colony monitoring program is to determine the annual total number of nests and estimate mean clutch size in order to evaluate long-term breeding population health. The methods for this measure involve an annual systematic census on Tern Islands over a 1-2 day period in mid-to late June during the late incubation stage. Observers are separated by 2 m along a line that transects each island in a sweeping NE-SW direction, and record the number of nests that contain ≥ 1 egg between them and the nearest observer; either to their right when walking in a NE direction or to their left when walking in a SW direction. In addition, clutch sizes of 3 or 4 randomly selected nests are recorded by each observer during these individual transects. Field crew leaders delineate covered island areas with survey flags at frequent intervals along census line extremities to ensure coverage of the entire colony.