Assessing avian diversity and red squirrel occurrence in fragmented high-altitude mountain pine forests of the central French Pyrenees: A dataset of point counts

In the spring of 1987, point-count surveys of breeding birds (passerines and picidae) were conducted, resulting in a dataset of 197 counts. The purpose was to analyze the effects of forest fragmentation on bird community composition in a mountain pine forest located in the Néouvielle National Nature Reserve in the central French Pyrenees between 1800 and 2400 metres. The study aimed to differentiate between the impacts of landscape factors (patch area, isolation) and habitat characteristics (altitude, vegetation structure). Additional information was gathered regarding the presence of Common Crossbill (Loxia curvirostra), Great Spotted Woodpecker (Dendrocopos major), Red Squirrel (Sciurus vulgaris), and Capercaillie (Tetrao urogallus) in the forest. The sampling design ensured that the selected patches represented a wide range of sizes and distances to the nearest large pine patch or low-altitude forest stand. Bird sampling utilized the point-count technique [3], focusing on singing passerines and Picidae within a 50-metre radius. The altitude, the percentage of open areas, of stones, boulders and of herbaceous and ligneous plant cover at various heights, the canopy height and number of dead trees, along with landscape variables describing patch size and isolation from large pine stands or low-altitude forests, were assessed for each point count. This dataset offers insight into the breeding bird community and squirrel occurrence in a typical high-altitude mountain pine forest in the Pyrenees in 1987, serving as a baseline for future comparisons to study changes in bird and squirrel populations, the impact of climate change, habitat fragmentation, and conservation priorities. These data aim to inspire further research and enhance our understanding of bird and squirrel ecology in mountain regions.


a b s t r a c t
In the spring of 1987, point-count surveys of breeding birds (passerines and picidae) were conducted, resulting in a dataset of 197 counts.The purpose was to analyze the effects of forest fragmentation on bird community composition in a mountain pine forest located in the Néouvielle National Nature Reserve in the central French Pyrenees between 1800 and 2400 metres.The study aimed to differentiate between the impacts of landscape factors (patch area, isolation) and habitat characteristics (altitude, vegetation structure).Additional information was gathered regarding the presence of Common Crossbill (Loxia curvirostra), Great Spotted Woodpecker (Dendrocopos major), Red Squirrel (Sciurus vulgaris), and Capercaillie (Tetrao urogallus) in the forest.The sampling design ensured that the selected patches represented a wide range of sizes and distances to the nearest large pine patch or low-altitude forest stand.Bird sampling utilized the pointcount technique [3], focusing on singing passerines and Picidae within a 50-metre radius.The altitude, the percentage of open areas, of stones, boulders and of herbaceous and ligneous plant cover at various heights, the canopy height and number of dead trees, along with landscape variables describing patch size and isolation from large pine stands or low-altitude forests, were assessed for each point count.This dataset offers insight into the breeding bird community and squirrel occurrence in a typical high-altitude mountain pine forest in the Pyrenees in 1987, serving as a baseline for future comparisons to study changes in bird and squirrel populations, the impact of climate change, habitat fragmentation, and conservation priorities.These data aim to inspire further research and enhance our understanding of bird and squirrel ecology in mountain regions .
© • These data should be of interest to researchers concerned with the evolution of biodiversity or the abundance of species of interest since 1987 in mountainous areas, due to several drivers of change such as climate change or forest fragmentation.Each point count is marked on a map and new counts could easily be carried out at the same locations.• These data should be useful for biogeographical comparisons with other mountain or lowland sites in terms of bird communities and squirrel occurrence.

Background
The extent and pattern of mountain pine forests are limited by geomorphology, altitude, fire and grazing.As a consequence, pine forests are fragmented into patches of different size, surrounded by a more or less rocky grassland and by heaths.Pine fragmentation in Néouvielle, a massif in the central French Pyrenees, represents a current situation in high altitude forests.Pine forests are sometimes connected with low-altitude forests, which harbour silver firs (Abies pectinata L.), beeches (Fagus sylvatica L.) and larch (Larix decidua L.).
The surveys carried out give a good picture of the bird communities and squirrel occurrence in the fragmented mountain pine forests of the high Pyrenees at the end of the 1980s.The climate was colder then, and our data could be used as a reference for studies on the evolution of bird communities and squirrel occurrence as a result of climate change that has taken place in recent decades.
Interestingly, these data could be compared to those recorded in the early 1980s in mountain pine forests of the eastern Pyrenees [ 1 ].

Data Description
The dataset, which is available on Recherche Data Gouv [ 2 ], includes 197 records of Red Squirrel and breeding birds ("Neouvielle_signs_of_presence.tab" and "Neouvielle_birds.tab")from mountain pine forests at altitudes between 1800 and 2400 m in the Néouvielle National Nature Reserve in the central French Pyrenees ( Fig. 1 and "Neouvielle_maps.pdf").A total of 16 birds' species (14 by song and 2 by other signs of presence) were recorded in spring 1987 ( Tables 1  and 2 ).
The forests are fragmented into patches of varying sizes surrounded by rocky grasslands and heaths.Some pine forests are connected with lower altitude forests.For each record, the area of  the forest stand containing the record and the distance to the nearest low-altitude forest were estimated.Forest patches of more than 50 ha were classified as large.Then, for records in forest stands smaller than 50 ha, the distance to the nearest large pine stand was estimated, otherwise it was set to zero ("Neouvielle_fragm.tab").
The meaning of the rows and columns in the four files of the dataset is explained in a readme file ("Readme.pdf").

Experimental Design, Materials and Methods
Birds were sampled using the point-count technique [ 3 ] within a limited distance of 50 m around the observer.Singing passerines and picidae were recorded for 20 min in spring mornings under fair weather conditions (no wind or rain).The bird species were identified by expert ornithologists (F.L. and M.G.).
Due to an exceptionally low number of pine cones in 1987, the Common Crossbill, a typical bird of these forests, was absent.The occurrence of pine cones consumed by crossbills in the previous year was noted on the ground within 50 m around the observer, as well as those consumed by woodpeckers and squirrels.Capercaillie, which are difficult to count using the point count technique, were recorded as droppings within 50 m of the observer.
Points-counts were located in three areas of the Néouvielle National Nature Reserve ( Fig. 1 ).Their positions are indicated on Figs.2-4 .Habitat descriptors were evaluated within a 50-metre radius of the point-count site.Plant cover was estimated through comparison with reference drawings depicting imaginary cover levels of 5 %, 10 %, and so on [ 4 ].The altitude was measured using an altimeter and the IGN map at a 1:25,0 0 0 scale.
The values of the landscape variables, describing both patch size and isolation from either large pine stands or low-altitude forest, were evaluated from 1/25,0 0 0 IGN maps and from 1/20,0 0 0 IGN aerial photographs .

Limitations
Not applicable .

Fig. 1 .
Fig. 1.Location of the central Pyrenees and the three main study areas on the topographic map provided by openstreet map.The current forests are represented in green (this coverage may differ from that of 1987).

Fig. 2 .
Fig. 2. Location of the point-counts in the first study area.

Fig. 3 .
Fig. 3. Location of the point-counts in the second study area.

Fig. 4 .
Fig. 4. Location of the point-counts in the third study area.
These data provide an overview of bird communities and Red Squirrel occurrences in the mountain pine forests of the central Pyrenees in the late 1980s.•Additionally, these data indicate the altitude, cover of open areas, stones, boulders and vegetation at different heights, canopy height and number of dead trees, which characterize the surveyed habitats, together with forest patch area and isolation.• These data can be valuable for researchers studying bird communities, biodiversity, Red Squirrel occurrence, and typical mountain species such as Capercaillie, and for conservation actors.

Table 1
Frequency of birds recorded using the point count technique (% of total point-counts).

Table 2
Frequency of capercaillie droppings and pine cones consumed by birds and squirrels in 1986 (% of total point counts).

Table 3
Habitat and landscape variables estimated for each sampling point.