Dataset of Passerine bird communities in a Mediterranean high mountain (Sierra Nevada, Spain)

Abstract In this data paper, a dataset of passerine bird communities is described in Sierra Nevada, a Mediterranean high mountain located in southern Spain. The dataset includes occurrence data from bird surveys conducted in four representative ecosystem types of Sierra Nevada from 2008 to 2015. For each visit, bird species numbers as well as distance to the transect line were recorded. A total of 27847 occurrence records were compiled with accompanying measurements on distance to the transect and animal counts. All records are of species in the order Passeriformes. Records of 16 different families and 44 genera were collected. Some of the taxa in the dataset are included in the European Red List. This dataset belongs to the Sierra Nevada Global-Change Observatory (OBSNEV), a long-term research project designed to compile socio-ecological information on the major ecosystem types in order to identify the impacts of global change in this area.


Introduction
Birds are among the most suitable groups of organisms for assessing species vulnerability to climate change (Pacifi et al. 2015). There is scientific evidence of the impact of climate change on bird communities (Crick 2004, Pearce-Higgins and Green 2014, Pearce-Higgins et al. 2015. Most studies supporting such impacts are based on longterm datasets (e.g. Gregory et al. 2009). Long-term datasets have been recognized as a key component for monitoring biodiversity (Magurran et al. 2010), and are considered one of the major requirements to identify changes in phenology (Sanz 2002). However, long-term monitoring programs are often difficult to develop. In this sense, reviewing old studies can help to integrate short-term studies into long-term datasets, providing a potential source of data to assess changes in ecological communities (Sanz 2002, Müller et al. 2010. This is relevant for the Mediterranean region, where more bird studies as well as available long-term datasets (Sanz 2002) are needed, especially considering that predicted levels in species richness have shown a sharp decrease in the southern regions of Europe (Barbet-Massin et al. 2012).
In this paper, a dataset of passerine bird communities is described from Sierra Nevada, a Mediterranean high mountain region in southern Spain. The dataset comes from Sierra Nevada Global Change Observatory (OBSNEV), a monitoring programme designed to evaluate the potential impacts of global change in this mountain area. Monitoring methodologies of the OBSNEV include revisiting old plots to assess long-term population trends, changes in phenology, and shifts in community composition, among other parameters.
Studies of bird communities in the Sierra Nevada mountain region go back to the 1850s, with the first published records of field observations recorded by ornithologists (Pleguezuelos 1991, Garzón 2012. A recent review of the birds in the Sierra Nevada was made by Garzón and Henares (2012). All these works include passerines, but specific studies focusing specifically on passerine bird communities on this mountain region were conducted during the 1980s (Zamora and Camacho 1984, Zamora 1987a, 1987b, 1988a, 1988b, 1990. The dataset presented here contributes knowledge about the passerines in this area, enabling assessments of population trends (e.g. Zamora and Barea-Azcón 2015).
• Evaluate the functioning of ecosystems in the Sierra Nevada Nature Reserve, their natural processes and dynamics over a medium-term timescale. • Identify population dynamics, phenological changes, and conservation issues regarding key species that could be considered indicators of ecological processes. • Identify the impact of global change on monitored species, ecosystems, and natural resources, providing an overview of trends of change that could help foster ecosystem resilience. • Design mechanisms to assess the effectiveness and efficiency of management activities performed in the Sierra Nevada in order to implement an adaptive management framework. • Help to disseminate information of general interest concerning the values and importance of Sierra Nevada. The Sierra Nevada Global Change Observatory has four cornerstones: • A monitoring programme with 40 methodologies that collect information on ecosystem functioning (Aspizua et al. 2012(Aspizua et al. , 2014. • An information system to store and manage all the information gathered (http:// obsnev.es/linaria.html -Pérez-Pérez et al. 2012; Free access upon registration). • A plan to promote adaptive management of natural resources using the data amassed through the monitoring programme.  (Hoffmann et al. 2014), eLTER (H2020 project. www.lter-europe.net/projects/eLTER), ECOPOTEN-TIAL (H2020 project. www.ecopotential-project.eu/) and ADAPTAMED (Life project).

Taxonomic coverage
This dataset includes a total of 27847 records of the order Passeriformes with 16 families represented ( Figure 2). Nearly one third of the specimens belong to the family Fringillidae. A total of 44 genera are represented in this collection, with Emberiza, Cyanistes, Turdus, Fringilla and Parus having the highest number of records ( Figure  3). Of this dataset 70 species appear in the European Red List (BirdLife International 2015): 67 are categorized as Least Concern, 2 is considered Near Threatened, and 1 is considered as Vulnerable (Table 1). According to the Spanish Red List (Madroño et al. 2004), 3 species in this dataset are placed in the Near Threatened category, 1 is listed as Vulnerable and 1 as Least Concern (Table 1).

Taxonomic ranks
Kingdom: Animalia Phylum: Chordata Subphylum: Craniata Class: Aves Order: Passeriformes Family: Aegithalidae, Alaudidae, Certhiidae, Cinclidae, Corvidae, Fringillidae, Laniidae, Motacillidae, Muscicapidae, Paridae, Passeridae, Phylloscopidae, Sittidae, Sturnidae, Sylviidae, Turdidae    (Gutiérrez et al. 2012, De Juana et al. 2004, 2007, 2009a, 2009b, 2010a, 2010b). e English common names (Gill and Donsker 2015).  also for winter-visiting species due to a great production of fruits from the end of the summer to the beginning of winter. Transects (n=4) in this habitat are located between 1450 and 2060 m a.s.l. (average: 1790 m a.s.l.). • Common juniper and Spanish juniper scrublands: vegetation in these localities is composed mainly of common juniper (Juniperus communis), Spanish juniper (Juniperus sabina). Cytisus galianoi and Genista baetica are also im-portant species in these ecosystems. These scrublands rarely exceed 60 cm in height and appear intermingled with rocks and stony ground. Transects (n=4) located in this ecosystems cover an elevational range from 2000 to 2300 m a.s.l. (average: 2150 m a.s.l.). • High-summit ecosystems: composed by typical Alpine landscape. These ecosystems are characterized by rocky outcrops that originated from glacial activity, pastureland, small snow beds, and glacial lagoons. The four transects representing this Mediterranean high-mountain habitat span an elevational gradient from 2280 to 3100 m a.s.l., with an average elevation of 2580 m a.s.l. Sampling description: The sampling procedure was the line-transect method (Verner 1985), with a bandwidth of 100 m, with 50 m on each side of the line ( Barea-Azcón et al. 2014). Each 50 m band was divided into five ranges parallel to the line transect (comprising a 10 m width each one). A total of 16 transects were sampled with lengths of 1.9 to 3 km ( Table 2). Sight and sound records within the sample area were considered contacts. All transects were sampled in the early morning, under appropriate climatic conditions. The observer walked at a constant speed of 2 to 4 km/h. Transects are repeated at least once per month, snow cover permitting. This implies that the sites located at the higher elevations were sampled only from late spring to early autumn.

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Method step description: All data were stored in a normalized database (Post-greSQL) and incorporated into the Information System of Sierra Nevada Global-Change Observatory. Taxonomic and spatial validations were made on this database (see Quality-control description). A custom-made SQL view of the database was performed to gather occurrence data and other variables associated with occurrence data, specifically: • Bird Count: number of individuals recorded by the observer within transect (see Sampling description) • Distance: distance of the contact (bird) from transect line. The distance was estimated by eye. The occurrence and measurement data were accommodated to fulfil the Darwin Core Standard (Wieczorek et al. 2009(Wieczorek et al. , 2012. We used Darwin Core Archive Validator tool (http://tools.gbif.org/dwca-validator/) to check whether the dataset met Darwin Core specifications. The Integrated Publishing Toolkit (IPT v2.0.5) (Robertson et al. 2014) of the Spanish node of the Global Biodiversity Information Facility (GBIF) (http://www.gbif.es/ipt) was used both to upload the Darwin Core Archive and to fill out the metadata.
For the measurement data, the Darwin Core elements included were: occurren-ceId, measurementID, measurementType, measurementValue, measurementAccuracy, measurementUnit, measurementDeterminedDate, measurementDeterminedBy, meas-urementMethod. Quality control description: The sampling transects were georeferenced using a hand held GPS device (WGS 84 Datum) with an accuracy of ±5 m. We also used colour digital orthophotographs provided by the Andalusian Cartography Institute and GIS (ArcGIS 9.2; ESRI, Redlands, California, USA) to verify that the geographical coordinates of the transects were correct (Chapman and Wieczorek 2006).
For field identification, several field guides were used Varela 2000, Jonsson 2001). The scientific names were checked with database of the IOC World Bird List (v 5.52) (Gill and Donsker 2015). We also used the R package taxize Szocs 2013, Chamberlain et al. 2014) to verify the taxonomical classification.

Dataset description
Object name: Darwin Core Archive Dataset of Passerine bird communities in a Mediterranean high mountain (Sierra Nevada, Spain) Character encoding: UTF-8