Census of breeding birds in the Pyrenees in the early 1980s: A publicly available dataset for ecological research

The Pyrenees is a mountain range in south-western Europe that supports a rich diversity of bird species. In 1981, point count surveys of breeding birds (passerines and picidae) were carried out in the Vanera valley, a valley in the eastern Pyrenees, resulting in a data set of 228 counts. These data provide valuable information on the distribution and abundance of bird populations on 5350 ha of heterogeneous land (including cropland, grasslands, heaths and river banks, and pine forest) at altitudes ranging from 1100 to 2600 meters. Additional point count surveys were carried out in the pine forest from 1982 to 1985, resulting in a data set of 144 counts. Habitat descriptors (percentage of herbaceous and ligneous plant cover at different heights - 0-1m, 1-4m and more than 8m; vegetation type) and altitude were assessed around each point count. This dataset provides a complete picture of the breeding bird community in a typical valley of eastern Pyrenees in the early 1980s, which could be compared with future censuses to contribute to a variety of research questions, such as quantifying changes in birds between the early 1980s and now in mountain areas, understanding the effects of climate change on bird populations, examining the effects of habitat fragmentation and land-use change, and identifying priority areas for conservation and management. These data could inspire new research and contribute to our collective understanding of bird ecology in the Pyrenees.


a b s t r a c t
The Pyrenees is a mountain range in south-western Europe that supports a rich diversity of bird species.In 1981, point count surveys of breeding birds (passerines and picidae) were carried out in the Vanera valley, a valley in the eastern Pyrenees, resulting in a data set of 228 counts.These data provide valuable information on the distribution and abundance of bird populations on 5350 ha of heterogeneous land (including cropland, grasslands, heaths and river banks, and pine forest) at altitudes ranging from 1100 to 2600 meters.Additional point count surveys were carried out in the pine forest from 1982 to 1985, resulting in a data set of 144 counts.Habitat descriptors (percentage of herbaceous and ligneous plant cover at different heights -0-1m, 1-4m and more than 8m; vegetation type) and altitude were assessed around each point count.This dataset provides a complete picture of the breeding bird community in a typical valley of eastern Pyrenees in the early 1980s, which could be compared with future censuses to contribute to a variety of research questions, such as quantifying changes in birds between the early 1980s and now in mountain areas, understanding the effects of climate change on bird populations, examining the effects of habitat frag-mentation and land-use change, and identifying priority areas for conservation and management.These data could inspire new research and contribute to our collective understanding of bird ecology in the Pyrenees. ©

Value of the Data
• These data give a picture of the bird communities in the Pyrenees in the early 1980s.They are useful for differentiating bird communities in different habitats and according to altitude.They are also useful for analyzing the stability of pine communities over 5 years.• In addition to birds, these data indicate the altitude, vegetation type and vegetation cover at different heights, which characterize the habitats surveyed • These data can be useful for researchers working on bird communities and biodiversity, but also on typical mountain species such as the Common Crossbill.• These data should be of interest to researchers concerned with the evolution of biodiversity or the abundance of species of interest since the 1980s in Mediterranean mountain areas.
Each point count is positioned on a map and new counts could easily be carried out at the same locations.• These data should be useful for biogeographical comparisons of bird communities with other mountain or lowland sites.

Objective
The surveys carried out give a good picture of the bird communities living in the different environments of a valley in the eastern Pyrenees, the Vanera valley, in the 1980s.The climate was colder then, and the region has experienced frequent heat waves and droughts in recent decades.The land cover is also slightly different today from what it was in the 1980s, due to changes in human activities.Our data could be used as a reference (possibly together with others collected at other sites in the Pyrenees in the same years) for studies on the evolution of bird communities as a result of global changes that have taken place in recent decades.

Data Description
The data presented here consist of records of breeding birds from fields, grasslands, heaths and forests at altitudes between 110 0 and 260 0 m in the Vanera valley, a typical valley in the eastern Pyrenees ( Fig. 1 ).A total of 60 species and 5305 individuals were recorded ( Table 1 ).In 1981, 228 bird counts were carried out on 5350 ha of heterogeneous land ( Fig. 2 ).In 1982In , 1983In , 1984In and 1985, 75, 22, 26 , 75, 22, 26 and 21 bird counts respectively were made only in the pine forest (30% of the study area).The percentage of herbaceous and ligneous plant cover at different heights (0-1 m, 1-4 m and more than 8 m) was assessed within a 50 m radius of the bird count site.In addition, altitude was recorded and nine vegetation types were defined: cropland, hill heath and river banks, montane heath, Scots pine (Pinus sylvestris L.) forest, montane mountain pine (Pinus uncinata Ram) forest, subalpine mountain pine forest, subalpine heath, subalpine grassland, and alpine grassland ( Fig. 2 ).

Experimental Design, Materials and Methods
Birds were sampled using the point-count technique with unlimited distance [1] .Singing passerines and picidae were recorded for 20 min in spring mornings.The bird species were identified by expertise ornithologist (F.L. and M.G.).
Point-counts were conducted in the centre of 0.025 km ² square cells in fair weather (no wind or rain).The cells were mainly situated on a grid that covered the study area ( Figs. 3-7 ).Habitat descriptors were evaluated within a 50 m radius of the point-count site.Plants cover were estimated through comparison with reference drawings depicting imaginary cover levels of 5%, 10%, and so on [2] .The altitude was measured using an altimeter and the IGN map at 1:50,0 0 0 scale.

Fig. 1 .
Fig. 1.Location of the Eastern Pyrenees and the study area in blue on the topographic map provided by openstreet map.Forested areas are shown in green.

Fig. 2 .
Fig. 2. Vegetation types found in the study area.

Fig. 3 .
Fig. 3. Location of the 228 point counts surveyed in 1981 on the topographic map of the Vanera valley.The name of the grid points is 1XY (X = abscissa and Y = ordinate).For example, the first point on the top left of the grid is 1EA.The labels of the points outside the grid are shown on the map.

Fig.
Fig. Location of the 75 point counts surveyed in 1982 on the topographic map of the Vanera valley.The name of the grid points is 1XY (X = abscissa and Y = ordinate).For example, the first point on the top left of the grid is 2EH.

Fig. 5 .
Fig. 5. Location of the 22 point counts surveyed in 1983 on the topographic map of the Vanera valley.The name of the grid points is 1XY (X = abscissa and Y = ordinate).For example, the first point on the top left of the grid is 1NL.

Fig. 6 .
Fig. 6.Location of the 26 point counts surveyed in 1984 on the topographic map of the Vanera valley.The name of the grid points is 1XY (X = abscissa and Y = ordinate).For example, the on the top the grid is 2NK.

Fig. 7 .
Fig. 7. Location of the 21 point counts surveyed in 1985 on the topographic map of the Vanera valley.The name of the grid points is 1XY (X = abscissa and Y = ordinate).For example, the first point on the top of the grid is 2NK.

Table 1
Total number of individuals recorded per bird species per year during point counts in the Vanera valley, Eastern Pyrenees.