Breeding and wintering populations are monitored using internationally standardized methods described by, among others, Walsh et al. 1995, and translated to a simplified Norwegian version intended for a limited number of species by Follestad & Lorentsen in 2011 (PDF, 4.0 MB). The practical work is simply all about counting birds or nests.
Nests and individuals in sampling plots
When monitoring breeding seabird populations, the standard unit for most species is ‘apparently occupied nest or nest site’. This is usually a nest containing or capable of holding eggs or chicks. For the Atlantic puffin, the unit is ‘apparently occupied burrow’, while for others (guillemots) it is the number of adult individuals in the colony (or sampling plot). Counts are either made at the colony scale (as for gulls) or in permanently defined sampling plots covering small parts of the colony (e.g. for kittiwakes, puffins and guillemots). The sampling plots are delineated on photos (a copy is kept by the fieldworker, while the original is saved for future reference), and relevant information regarding the sampling plot is noted. This includes a thorough documentation of the point from which the counting is made, to ensure that the work is conducted the same way each year. The objective is to document the work well enough to enable anyone to pick up the notes and photos 100 years later and count in the exact same way as we do it today.
Counting at the breeding sites
For most species, the population monitoring entails colonies being visited physically, but for species with a more scattered nest distribution (e.g. the great cormorant), counts are made from a boat or aircraft. Most of the work in the colonies is conducted by scientific staff from the Norwegian Institute for Nature Research (NINA) and the Norwegian Polar Institute (NPI), but private individuals, local branches of the Norwegian Ornithological Society (NOF), Norwegian Nature Surveillance (SNO) and several other institutions also take part.
Counting in the winter
We usually monitor wintering seabirds in February (South Norway) and March (North Norway). The coastal areas of interest are divided into sections, usually 1-2 km long. The borders between them are so defined that the sections are easily distinguished, for example as a straight line from a headland to a navigation mark. Field workers count all waterbirds within each section through binoculars or telescope.