Survey years	1999-2002
Participants	518
Participants who censused 1x1 UTM squares	239
Participants who have only returned complementary sheets	256
Total sheets	4.184
UTM 10x10 square sheets	439
Complementary sheets	3.745
Total data	1.129.078
Breeding evidences (e.g. male singing persistently,nest-building...)	108.838
Presence in 1x1 UTM censuses	92.673
Absence in 1x1 UTM censuses	927.567
Surveyed 10x10 UTM squares	385
1x1 UTM squares with diurnal censuses	3.077
1x1 UTM squares with nocturnal censuses	1.204
1x1 UTM squares with diurnal censuses made by semi-professionals	522
1x1 UTM squares with nocturnal censuses made by semi-professionals	233
Breeding evidences (possible, probable, confirmed, summer records of non-breeding birds) shown in the distribution maps	60.281
Shown in 1999-2002 distribution maps	32.238
Without considering summer records of non-breeding birds	30.864
Shown in 1975-1983 distribution maps	28.043
Breeding species included in the book's main body	232
Complementary species	94
New breeding species	21
Threatened species (CR, EN or VU)	67

Species per 10x10 UTM squares in the 1999-2002 atlas

The map shows the number of breeding species recorded for each 10x10 UTM square in this atlas (1999-2002). The mean number of species recorded for each 10x10 UTM square is 80 (range = 6-123, n = 384); if we consider only the squares with more than 50% of Catalan territory (thus excluding many of the coastal and border squares), this mean is 86 (range = 48-123, n = 321). The square CH54, the artificial breakwater in Tarragona harbour, was surveyed, but no breeding species were found. At 10x10 UTM scale there is no clear geographical pattern regarding the number of species recorded. Nevertheless, it seems that the northern third of the country has higher values, and that some areas such as the plains of Lleida, Les Guilleries or Les Gavarres, characterised by homogeneous landscapes, have fewer number of breeding species per square.



Species per 10x10 UTM squares in the 1975-1983 atlas

The map shows the number of breeding species recorded for each 10x10 UTM square in the previous atlas (1975-1983). The mean number of species recorded for each 10x10 UTM square was 73 (range = 9-118, n = 392); if we consider only the squares with more than 50% of Catalan territory (thus excluding many of the coastal and border squares), this mean was 76 (range = 20-118, n = 231). The three blank squares correspond to squares that were not surveyed in the 1975-1983 atlas. The higher number of species recorded in each 10x10 UTM square in the 1999-2002 atlas compared with the 1975-1983 atlas can be attributed essentially to the greater sampling effort in the present atlas and should not be interpreted as a real increase in the number of species breeding in each 10x10 UTM square. However, there is a common marked spatial pattern, with a higher concentration of species in many Pyrenean areas in the first atlas than in the present one.



Field sheets per 10x10 UTM

The map shows the number of field sheets that contributors returned for each 10x10 UTM square. In total, 439 UTM 10x10 square sheets and 3,745 complementary sheets were submitted by participants. The geographical distribution of the number of UTM 10x10 square sheets is very similar to that of the number of contributors, and most sheets were received for zones such as the Barcelona conurbation, the Lleida plains, the Pyrenees and the country's main wetlands.