Degrees of Breeding Evidence and Survey Activity

Degrees of breeding evidence

Degree of breeding evidence in a given grid has been expressed using indices from 1 to 8. Indices 6–8 have been divided into sub-indices. The same indices with the same definitions were used also in the first and second breeding bird atlases.

A.  Breeding unlikely (index 1)

  • 1. Species detected in the grid during the breeding season, but almost certainly does not breed there. This class includes e.g. birds that have stopped for several days during migration or that are clearly non-breeders. Birds detected in migration flight or at a short stop are not included.

B. Possible breeding (indices 2–3)

  • 2 . A solitary bird detected once (e.g. a singing male) in suitable breeding habitat, and breeding of the species in the grid is possible. The site has been visited only once or the bird has been observed only once despite multiple visits.
  • 3 . A pair detected once in a suitable breeding habitat, and breeding of the species in the grid is possible.

C. Probable breeding (indices 4–6, subindices 61–66)

  • 4 . A singing or a displaying male observed at the same site in different days.
  • 5 . A female or a pair observed at the same site in different days .
  • 6 . A bird or a pair observed
    • 61: visiting frequently at the probable nest,
    • 62: building a nest,
    • 63: giving alarm calls because of proximity to nest or brood,
    • 64: displaying broken wing -act, or
    • 65: attacking the observer.
    • 66: Nest found with fresh nest material or remains of food; no direct evidence of eggs or young found.

D. Confirmed breeding (indices 7–8, subindices 71-75 ja 81-82)

  • 7 . Indirect evidence of verified breeding detected :
    • 71: nest found with signs indicating that is has been used in the same year (eggs or egg remains, or remains of nestlings)
    • 72: a bird seen entering or coming out from the nest in a way that suggests breeding (eggs or nestlings not seen)
    • 73: fledglings or young detected so that they can be assumed to have hatched within the grid
    • 74: a parent carrying food to nestlings or faeces of nestlings away from the nest (it is likely that the nest was located in the grid)
    • 75: an incubating bird seen in the nest.
  • 8 . Direct evidence of a verified breeding detected:
    • 81: begging or other calls of nestlings heard from the nest
    • 82: a nest found with eggs or nestlings.

Survey activity

Survey activity of each grid has been calculated as a weighed sum of degrees of breeding evidence for each species detected in the grid. Species with confirmed breeding were given score 3, probable breeding resulted in score 2 and possible breeding resulted in score1. Thus, survey activity of a given grid is influenced by both number of species and degree of breeding evidence of each species. For example, a combination of 15 confirmed breeding species, 10 probable breeding species and 12 possible breeding species will result in survey activity of 77.

The survey activity was classified into six categories: 0 = no observations in the grid, 1 = only occasional observations, 2 = the grid was fairly-well surveyed, 3 = the grid was satisfactorily surveyed, 4 = the grid was well-surveyed and 5 = the grid was thoroughly surveyed. These categories are used on the atlas maps to illustrate the survey efficiency. Lower and upper limits of weighed sums of degrees of breeding evidence have been determined for each category. In general, the limit values are lower in the north because the number of potential breeding species is lower there. Further, also the amount of land area has been taken into account when determining lower and upper category limits.