Survey methods

In most atlas squares, a breeding Black Redstart is easy to find, whereas detecting the Eurasian Woodcock may require considerable effort and special surveys. To account for such differences, we divided all breeding species into five categories. In addition to the categories «widespread species», «rare species» and «colonial species» used in 1993–1996, the 2013–2016 atlas defined two additional groups, namely «rare species on the Central Plateau and in the Jura» and «colonial species in settlements».

Since our aim was to record all breeding species present in each atlas square, we set a minimum target of one valid record per atlas square for all species. The habitats of species not classed as widespread were to be surveyed with special care, so that data on these species would be available from as many square kilometres as possible. The following guidelines applied to the five categories (category codes use the first letter of the German category names):

Widespread species (W)

93 species were classed as widespread species (W). These are species considered widespread throughout Switzerland or at least in certain regions. They were mainly recorded using simplified territory mapping in preselected kilometre squares. If the species were not found during the surveys, the search was extended to the remaining areas of the atlas square.

Rare species (R and R*)

The «rare species» category (R) comprised 126 species. All observations had to be recorded with their exact location. Fieldworkers were asked to search as many potential habitats as possible in each atlas square. The aim was to obtain records from several square kilometres per atlas square, if possible. Eleven of these rare species (mainly nocturnal species) were considered difficult to record (R*). To prevent fieldwork effort from becoming too onerous, one valid record per atlas square was sufficient for these species. Observers were advised to use call playback very sparingly, if at all.

While one valid record per species was considered sufficient for all rare species during the 1993–1996 surveys, observers for the 2013–2016 atlas were encouraged not to reduce the search effort once a species had been detected, but rather to extend their search to further potential habitats. The additional records gave us a more comprehensive picture of the species' distribution and allowed us to generate more accurate distribution maps.

Rare species on the Central Plateau and in the Jura (RPJ)

This category (RPJ) comprised nine species that are more or less widespread in the Alps, but rare or in steep decline on the Central Plateau and/or in the Jura: Common Cuckoo, Eurasian Wryneck, Eurasian Crag Martin, Water Pipit, Northern Wheatear, Ring Ouzel, Wallcreeper, Citril Finch and Redpoll. In an approach similar to the «rare species» category, observers were asked to visit as many potential habitats as possible per atlas square within the biogeographical regions of the Central Plateau and the Jura.

Colonial species (C)

The following ten species were classed as colonial species (C): Great Cormorant, Grey Heron, Northern Lapwing, Black-headed Gull, Yellow-legged Gull, Common Tern, Alpine Swift, Collared Sand Martin, Eurasian Jackdaw, and Rook. All known colonies of rare colony breeders such as Great Cormorant, Northern Lapwing, Black-headed Gull, Yellow-legged Gull and Common Tern have been well documented for many years via the Swiss Ornithological Institute's ongoing monitoring schemes. The atlas surveys therefore focussed on Grey Heron, Alpine Swift, Collared Sand Martin, Eurasian Jackdaw and Rook, whose populations are only systematically monitored in a few areas. Special priority was accorded these five more common colony breeders in 2014, when we asked observers to search for the species throughout the atlas square and record colony size and location as accurately as possible. In many cases, the colonies were counted every year. Our aim was to record distribution and colony size as fully as possible in each atlas square.

Colonial species in settlements (CS)

Common Swift and Northern House Martin mainly breed in colonies in settlements (CS), often in scattered sites. Attempting to count all colonies of these two species throughout their range would not have been realistic. We therefore focussed on colonies of at least ten pairs while welcoming records of smaller colonies.