The online software is the main part of Biologer (Fig. 2) handling 1) user registration and privileges (being users, editors and administrators), 2) taxonomic database (list of taxa, their localised names, descriptions, threat and conservation status), 3) species observations (data entry, verification and publication) and 4) communication with other software through a web service. An Android application was also developed for use during the fieldwork (Fig. 1b). It enables easy data entry by automatically filling user data, location with coordinates and coordinate precision, date and time of each observation. Besides field observations, the software allows editors to enter species observations digitalised from available scientific literature, while the entry for collection data is in the final phase of development. Easy transition from other software solutions is possible, since Biologer offers the option to import structured data from CSV tables.

An important step in publishing biodiversity data is the review process (Costello et al. 2013), which involves taxonomic experts (editors) from the Biologer community. They are responsible for checking each observation, approving the identification of taxa (species complex, species or subspecies) or marking the finding as unidentifiable. Unidentifiable records could be supplemented later on with detailed evidence for species observations (i.e. images of certain body parts) or reviewed and identified by more experienced editors. To track these activities, the history of changes is logged along with each species observation.

Data access is principally controlled by the users’ settings defining separate licences for images and observations, but we strongly suggest choosing open data for its greater applicability in both science and nature conservation (Groom et al. 2016). Access can also be restricted by the editors for particular taxa, if the survival of endangered local populations could be threatened by showing detailed occurrences on the maps. The species observations for these restricted taxa is shown as 10×10 km square, without precise coordinates. All species observations with open access can be viewed from the Contributor Area and saved as Comma Separated Value (CSV) file by registered users. In order to enhance cooperation with existing biodiversity portals, data can be exported using standardised Darwin Core terms (Wieczorek et al. 2012). Data from Biologer was successfully used in several projects, ranging from collecting species observations of dragonflies, reptiles and butterflies, reporting on butterfly species for Emerald network, to providing data for the desktop analysis in designating Natura 2000 in Serbia (EuropeAid/139336/DH/SER/RS). We have already used Biologer as the prime source of data for analysing distribution of Hermann’s tortoise (Golubović et al. 2019) and brown frogs (Urošević et al. 2018) and for updating the Red List of butterflies of Serbia (published in Maes et al. 2019).

Finally, Biologer offers a simple data browser from its main page (Fig. 1c). Each species overview is designed as an online encyclopaedia providing scientific and vernacular name, short descriptions, threat and legal status on national and international level, phenological graph, map of records within the country and a gallery of photos. Species descriptions are published with a Creative Commons licence to promote sharing of intellectual knowledge and are being updated by the editors.

Future perspectives

With the growing support from several local communities, one of our prime goals is to make the taxonomic database a separate component of the platform. The taxonomic database will provide a list of synonyms, country specific checklists, conservation and legal status for each country involved, local species names and descriptions, as well as an endpoint for communication with other components of Biologer. After completion of this task, we will be able to provide a single multilingual encyclopaedia on regional species diversity along with a content aggregation of open access data from all officially-involved Biologer communities on a single data server. Aggregated observations will be free to download or redistribute to global biodiversity databases according to the licences chosen by the users. We plan to enhance user experience by showing usage statistics, providing more detailed data overview and facilitating direct communication amongst users. Biologer could also support adding different types of data, such as species counts along transects or within delineated areas (polygons).

Biologer has been collecting observation data from Serbia since 2018 at biologer.org. Croatia joined our initiative registering at biologer.hr in 2019, while in 2020 Bosnia and Herzegovina started their data portal at biologer.ba. Currently, each country maintains its own server for data collecting and has its own community of users, while the Biologer application for Android devices allows choosing the prefered community. At the time of writing this manuscript, we have gathered 536 users (64% from Serbia, 25% from Croatia and 11% from Bosnia and Herzegovina) and collected 163,843 records from the field (Serbia 71%, Croatia 27%, Bosnia and Herzegovina 2%). Additionally, the Serbian data portal imported 33,458 digitalised literature records. It is interesting to note that users predominantly choose open data licences for their observation records. Most of the records (89%) are delivered under open access licences, 10% of data is accessible on the scale of 10×10 km, while only 1% of data is closed. Being issued under the MIT licence, Biologer software is available to the public and any organisation or individual could run it on a dedicated server and modify it for their own needs. A good example for this is the "Biologer Otis" application adapted for monitoring the great bustard (Otis tarda) population in Serbia. Our Project team will work on acquiring more developers and volunteers and establishing other local Biologer communities within the region.