Credits & licences

This guide is built on public datasets and on images under a Creative Commons licence or in the public domain. Below, first where the data come from — the checklist, the family tree, the measurements, the habitats and the distribution maps — and then the full list of photographs, giving the author, the licence and the source page for each file. Some photographs carry a non-commercial (NC) licence; the guide itself is non-commercial.

Where the data come from

The guide rests on a handful of public datasets. They are gathered here, with what each contributes and on what terms.

• ADW — Animal Diversity Web

  Field measurements for part of the species. Animal Diversity Web is the species database of the Museum of Zoology at the University of Michigan; its accounts are written by students and checked by the editors, and give head-body length, tail length and, where relevant, shoulder height. Only the figures are taken, not the text.

• Aoun & Bouratbine 2014, cutaneous leishmaniasis in North AfricaCC BY 4.0

  Which rodents act as reservoir hosts of Leishmania major in North Africa, and in which countries natural infections have been established. For two species in this guide that is an essential part of the story: the Fat Sand Rat has been found naturally infected in Libya, Algeria and Tunisia, and Shaw's Jird is the main infected animal in southern Morocco and has likewise been found infected in Algeria and Tunisia. The review appeared in Parasite 21:14 and carries a free licence, so the guide can cite it without reservation.

• Area Marina Protetta Golfo di Palmas

  The measurements of the Sardinian hare. The Golfo di Palmas marine protected area in south-western Sardinia describes the park's fauna; outside Italy the hare of Sardinia and Corsica is hardly ever measured separately.

• Bihari, Balogh & Pető 2009, the blind mole-rats of Hajdúbagosvrij toegankelijk in het REAL-archief van de Hongaarse Academie van Wetenschappen

  The field criterion by which a mole-rat mound is separated from a molehill. In Természetvédelmi Közlemények 15: 46-56, Zoltán Bihari, Péter Balogh and Noémi Pető describe the Hungarian population size and the space use of the species using the Hajdúbagos site, and give the rule this guide applies in the tracks-and-signs block of all eight species: mounds with a base diameter of more than sixty centimetres, tunnels of more than four centimetres across, and mounds spaced farther apart than a mole's point to the blind mole-rat. The authors add explicitly that certainty requires practical experience and is never complete — a caveat this guide carries over.

• Bugarski-Stanojević et al. 2022, the cryptic diversity of the leucodon complexCC BY

  The review from which this guide takes the assessment of the individual forms. In Animals 12(9): 1097, Vanja Bugarski-Stanojević and colleagues tabulate the chromosomal forms of Nannospalax leucodon with their 2n, fundamental number and distribution, and attach to each a judgement of threat: montanosyrmiensis endangered to critically endangered, montanoserbicus a form requiring monitoring. From this source also comes the central complaint that recurs on all eight pages: as long as these animals carry no official species name they cannot be taken up into any conservation instrument.

• Bugarski-Stanojević et al. 2024, the rediscovered blind mole-rat of SremCC BY

  The diameter of the burrow system — about five to seven centimetres — given in the tracks-and-signs block of all eight species, and the description of the habitat as steppe-like grassland, mountain steppe and sand steppe, with marshy ground avoided. In Animals 14(5): 774 the authors also show, with DNA from archived material and new captures, that the syrmiensis form, written off as extinct in the literature, still exists near Belgrade and Smederevo, while the type locality Stara Pazova and the Srem sites are empty — the clearest picture there is of how quickly these animals vanish from a landscape.

• CABI Compendium, the datasheet for Finlayson's Squirrelde databank zelf is niet vrij; alleen geciteerd

  The introduction history of Callosciurus finlaysonii in Italy, with the figures. The datasheet records that in 1981 four animals of the subspecies bocourti were released in a two-hectare town park at Acqui Terme (Piedmont) and that in the mid-1980s three to four pairs got out near Maratea in Basilicata; that both populations are increasing, the Maratea one exponentially; and that bark-stripping damage in the park of the northern introduction eventually affected some eighty per cent of the trees, with stone pine, oak, olive and carob as the chief victims and with the death of the tree where a stem is ringed right round. Without this sheet the guide could say that the species is in Italy but not since when, with how many animals, or to what effect.

• Biodiversity Conservation Center, Moscow (biodiversity.ru)

  The measurements of the Caucasian mountain souslik. The Moscow Biodiversity Conservation Center publishes species accounts from its own fieldwork and from the Russian-language literature.

• cicon.ru — the regional Red Data Books of Russia

  The measurements of the great jerboa and of Strand's birch mouse. This site gathers the species accounts from the regional Red Data Books of Russia, each with head-body length, tail length and weight.

• Compendium voor de Leefomgeving, the Muskrat indicator 1950–2025CC BY 4.0 (Compendium voor de Leefomgeving)

  The long series of figures behind Dutch muskrat control. The Compendium — the joint statistical resource of Statistics Netherlands, the Netherlands Environmental Assessment Agency, Wageningen University & Research and the National Institute for Public Health — gives the first Dutch record (1941, at Valkenswaard), the catch series from 1950, the peak of three to four hundred thousand animals a year at the start of this century, the decline since 2005, and the 84,438 animals caught in 2025 with the twenty-eight per cent rise on 2024. This guide takes the figures in the muskrat's status block from it.

• Cserkész 2011, new record of the Hungarian birch mouse

  The measurements of the Hungarian birch mouse. Hardly any measured animals of this species are known; this paper describes the capture that rediscovered it in Hungary and gives that animal's measurements.

• Cucchi et al. 2006, the description of the Cypriot mousehet artikel zelf is niet vrij; de gebruikte figuur is door de auteurs onder CC0 op Zenodo en Wikimedia Commons gezet

  The species Mus cypriacus itself. In Zootaxa 1241, Cucchi, Orth, Auffray, Renaud, Fabre, Catalan, Hadjisterkotis, Bonhomme and Vigne described the first new European mammal in decades, found in the vineyards and fields of Cyprus and recognisable by its larger ears, eyes and teeth and its two-coloured tail. This guide takes from the paper the type locality (the village of Alassa), the year and the authors, and the finding that the species is the last surviving endemic rodent of the island's Pleistocene fauna. The main photograph on the species page is figure 3 of that paper, released by the authors under CC0; the measurements in this guide do not come from here but from the Handbook of the Mammals of the World, so that a single tradition is kept.

• The Union list: Implementing Regulation (EU) 2016/1141 and its amendmentsHergebruik van EU-wetgeving is toegestaan (Besluit 2011/833/EU); de tekst zelf is niet auteursrechtelijk beschermd

  Which species went on the Union list, and when. The first list of 13 July 2016, in force from 3 August 2016, brought the Grey Squirrel, the Eastern Fox Squirrel, Pallas's Squirrel, the Siberian Chipmunk and the Coypu, among others, under the prohibitions; the first extension, Implementing Regulation 2017/1263, added the Muskrat on 2 August 2017, later amendments (2019, 2022) added further species, and Implementing Regulation 2025/1422 of 17 July 2025 added, among others, the North American Beaver and the American Mink, for those two species with effect from 7 August 2027. This guide uses those dates literally in the status blocks, and uses the list also to show who is not on it: the Eastern Chipmunk and the American Red Squirrel may still be kept and traded freely in Europe.

• Die Säugetiere Oberösterreichs, species account of the Alpine Field Mousevrij te lezen in het archief Zobodat (Biologiezentrum Linz); alleen geciteerd, de tekst zelf is niet vrij

  The natural history of the Alpine Field Mouse, the one species in this guide confined to the Alps and the one the ordinary works of reference pass over. The species account in the mammal atlas of Upper Austria supplies the year and authors of the species' recognition (Storch & Lütt, 1989), the habitat description up to and above the treeline, the breeding data (April to August or September, two to three litters averaging five to six young), the seasonal shift in diet with over half insects in April, the finding that tree seed counts for little in the winter store, and the two threats named: the isolation of woodland blocks and selective rodent control in forestry. The measurements in this guide do not come from here but from kleinsaeuger.at, so that a single tradition is kept.

• DREAL Provence-Alpes-Côte d'Azur on Pallas's Squirrelauteursrechtelijk beschermd; alleen geciteerd

  The French side of Pallas's Squirrel. The regional environment and housing directorate of Provence-Alpes-Côte d'Azur gives the two French seats of the fire — the Cap d'Antibes peninsula, where the species has been present since the late 1960s and now occupies the communes of Antibes-Juan-les-Pins and Vallauris, with stray animals as far as the Valmasque park north of the A8, and a second nucleus at Entressen (Istres) in the Bouches-du-Rhône discovered at the start of this century. It also names the damage this guide refers to: ringing of trees and shrubs, gnawing of telephone cables and garden hoses, eating of citrus fruit, and the suspicion of competition with the Red Squirrel; and the control plan launched in 2010.

• Dubey et al. 2007, the white-toothed shrews of the Mediterraneanhet artikel zelf is niet vrij; alleen geciteerd

  The whole story of Crocidura cypria. In Molecular Ecology 16:3438–3452, Dubey, Cosson, Magnanou, Vohralík, Benda, Frynta, Hutterer, Vogel and Vogel compared one hundred and forty-three cytochrome b sequences of white-toothed shrews around the Mediterranean and found a result that separates the islands: the Cypriot shrew reached the island about 1.54 million years ago, in the early Pleistocene, and so belongs to the rare group of island mammals of that age that have survived to the present, whereas the populations of Crete, Corsica and Menorca were introduced independently from the Middle East only in the Holocene, six to eight thousand years ago. This guide takes from it the species status, the age, and the observation that the appearance of a Mediterranean white-toothed shrew says nothing about its origin.

• El-Farhati et al. 2021, the history of the two North African hedgehogsCC BY 4.0

  The provenance of the North African Hedgehog in Europe, and the arrangement of both North African hedgehogs. In Vertebrate Zoology 71:799–811, El-Farhati, Khaldi, Ribas, Hizem, Nouira and Nicolas examined the mitochondrial DNA and the climatic suitability of Atelerix algirus and Paraechinus aethiopicus. This guide takes from it that A. algirus reached Spain, the Balearics and the Canary Islands recently and almost certainly through human agency, that in North Africa the species consists of two haplogroups and at the Last Glacial Maximum sat in separate refugia in south-western Morocco, along the Moroccan-Algerian coast and in Tunisia-Libya, that P. aethiopicus shows no phylogeographic structure and that nearly the whole Sahara was climatically suitable for it even then, and that the subspecies distinguished within North Africa do not hold — in either species. The paper is CC BY 4.0.

• EUNIS

  The habitats. EUNIS is the habitat classification of the European Environment Agency; this guide uses the A–J version, with ten main groups from open sea to built-up land and a few dozen formations beneath them. Each species carries only the habitats where it genuinely lives and feeds, at most seven. It is the same classification and the same set of photographs as in the European bird guide: the same continent, the same window.

• Gazzard, Macdonald & Rasmussen 2025, the state of Europe's hedgehogsCC BY 4.0

  The review on which the status block of the four hedgehog pages in this chapter rests. In Biological Conservation 304:111033, Abigail Gazzard, David W. Macdonald and Sophie Lund Rasmussen set Europe's five hedgehog species side by side and give for each the regional European assessment of 2023–2024, the known threats and the gaps in knowledge. This guide takes three things from it that are nowhere else assembled: that the Long-eared Hedgehog is Vulnerable in the European assessment and thus the continent's most threatened hedgehog, that it has gone from Ukraine and within Europe holds only in southern Russia and on Cyprus with an estimated fewer than thousands of animals; that Erinaceus concolor within Europe is confined to Chios, Samos, Kos and Rhodes and that genetic work is needed to fix its boundary with E. roumanicus; and that in one studied contact zone up to twenty per cent of hedgehogs carried a mixed genotype of E. europaeus and E. roumanicus. The paper is CC BY 4.0.

• GBIFCC BY 4.0

  The records behind the distribution maps. GBIF gathers data from museums, research projects and observer networks into one searchable whole; the maps in this guide draw the density of those records, not a drawn range boundary. Mammals are reported far less often than birds, so each cell is divided by the total number of mammal records in that same cell — otherwise the map shows where the observers walk. GBIF also mirrors the IUCN Red List, and the status of every species was checked along that route. Records from the Low Countries largely arrive through Observation.org.

• Handbook of the Mammals of the World (via Plazi)

  Field measurements for the species no European source gives a figure for — after Wikipedia the most used measurement source in this guide, above all for the voles, the ground squirrels and the bats. The Handbook of the Mammals of the World (Lynx Edicions) treats every mammal species in the world; the species treatments are available as separate text blocks in Plazi's TreatmentBank and were consulted along that route, not from the book itself. Where a name stands in brackets after the key, that is the name the treatment is filed under there.

• Hortobágy National Park — the Natura 2000 species account of the blind mole-rat

  The field measurements of the blind mole-rats of the Hungarian lowland, under the key HNP: head-body length 19 to 27 cm, weight 140 to 220 grams, and — the field on which almost no source says anything — a tail length of 0 to 0.2 cm. That last figure is why this source is here: the Handbook of the Mammals of the World, the Animal Diversity Web and the German reference works all simply state that a blind mole-rat has no external tail, without a measurement, and the Hungarian species account is the only source consulted that actually measures the rudimentary tail. The account also supplies the Hungarian distribution (Békés, Hajdú-Bihar, Bács-Kiskun and Jász-Nagykun-Szolnok), the description of the burrow system with shallow galleries at ten to fifteen centimetres and deep chambers to a hundred and fifty or a hundred and eighty, and the species' protected status in Hungary.

• IUCN Red ListCC BY-NC-ND 4.0 (teksten); de categorieën en jaartallen zijn feiten en worden hier alleen genoemd

  The category and the year of assessment for every species. The Mammal Diversity Database gives the category but not the year in which it was set, and that year often says more than the category itself: for the spiny mice and most of the gerbils in this guide the assessment dates from 2016, for Flower's Gerbil from 2008 — older than the taxonomic revision that changed that species' range. For each species the assessment was checked through the Red List reference recorded with the species.

• IUCN SSC Cat Specialist Group

  Field measurements for the cats. The Cat Specialist Group is the cat working group of the IUCN and keeps a fact sheet for every species with measurements, weight and range.

• kleinsaeuger.at

  The measurements of the northern birch mouse. This Austrian site describes the small mammals of central Europe with identification in the hand in mind, and gives the measurement series used in trapping work.

• Kruger Park (krugerpark.co.za)

  Alongside Wikipedia, the measurements of the Cape hare. That is an African species reaching into North Africa; the South African park accounts give measurements for it, the European sources do not.

• Kryštufek & Vohralík 2012, revision of the Palaearctic squirrels

  The measurements of the sousliks and of the Siberian chipmunk. This revision — Taxonomic revision of the Palaearctic rodents. Sciuridae: Xerinae 1 (Eutamias and Spermophilus), in Lynx (n.s.) 43 — remeasures museum material and gives head-body and tail length per species. For Spermophilus taurensis no other source carries measured series.

• Mammal Diversity DatabaseCC BY 4.0

  The sequence and arrangement of orders, families, genera and species, and for every species the author, the year, the authority parentheses, the original name combination and the type locality. The Mammal Diversity Database is the checklist of the American Society of Mammalogists and is updated continuously; this guide follows version 2.5 of 28 July 2026, with 6904 species. One source, including where it departs from GBIF: the MDD follows recent splits that the GBIF backbone has yet to adopt. The IUCN category for each species comes from the same file.

• Mammalian Species

  The measurements of the Anatolian souslik. Mammalian Species is the American Society of Mammalogists' series of species monographs: one species per account, with the measured series, the distribution and the literature.

• MarineBio

  The total length of the Mediterranean monk seal. MarineBio is an American marine education organisation. Note the measurement: for seals almost every source measures snout to hind-flipper tip rather than head-body length, and where that is so the guide says as much beside the figure.

• MITECO — Spanish Inventory of Terrestrial Species

  Field measurements of the Iberian and Macaronesian species. In the Inventario Español de Especies Terrestres the Spanish ministry for ecological transition publishes a sheet per species with measurements, weight, distribution and status. For the Barbary ground squirrel, the Basque vole, the peninsular field vole and the Iberian rabbit it is the most exact source within reach.

• Mossy Earth — the Croatian blind mole-rat project

  The only information this guide has on Croatia. The project page describes how the blind mole-rat was considered extinct in Croatia from 1984 and was found again in 2023 at Vučedol on the Danube, and how environmental DNA and fieldwork were then used to try to map the country's only known population. The page also names the local threats: agricultural intensification, urbanisation, infrastructure, and the chance that the animal will once more be treated as a farm pest. Which of the eight species is involved there has not been established, and this guide says so.

• Natural Earthpubliek domein

  The country outlines of the distribution maps. The boundaries are projected with a Lambert azimuthal equal-area projection centred on the window 29–71°N, 26°W–37°E, the same window as in the European bird guide, and reduced to a single drawing file. Natural Earth is public domain and asks for no attribution; it is listed here because a reader ought to know where the lines come from.

• Norwegian Polar Institute

  The measurements of the walrus, taken from the Svalbard animals. The Norwegian Polar Institute carries out the research on Svalbard's marine mammals and publishes a sheet per species with length and weight. For a species of which the map window sees almost none but wanderers, that is the fairer source.

• Netherlands Food and Consumer Product Safety Authority, Pallas's Squirrel factsheetauteursrechtelijk beschermd; alleen geciteerd

  The Dutch story of Pallas's Squirrel. The factsheet of the Office for Risk Assessment and Research of the Netherlands Food and Consumer Product Safety Authority gives the first Dutch record in the wild (1998), the damage the species did here — ringing of stout branches, damage to roof structures and to plastic piping in gardens — the finding that the population in the Weert region had been trapped out in 2017 and that the species was probably no longer present in the country afterwards, and the listing on the Union list from August 2016 with the transitional arrangement for private keepers. This guide takes the whole Dutch part of the species' range and status blocks from it.

• Németh et al. 2013, the revision of the blind mole-rats of the graecus grouphet artikel zelf is niet vrij; alleen geciteerd

  The three species into which the old Spalax graecus breaks up. In Zoological Journal of the Linnean Society 169(4):903–914, Németh, Homonnay, Krízsik, Csorba, Pavlíček, Hegyeli, Hadid, Sugár, Farkas and Csorba showed with mitochondrial DNA and skull measurements that antiquus of Transylvania and istricus of the Wallachian Plain are not subspecies but well-defined species of their own, forming with graecus a separate clade within Spalax. This guide takes from the paper the species status of three of its eight blind mole-rats, the skull characters on which it rests — the backward-extending nasals in graecus, the rostrum narrowed above and widened below in istricus — and the finding that the molecular data confirm the old, size-based separation of the greater blind mole-rats (Spalax) from the lesser (Nannospalax). Without this revision three species in this chapter would still stand under one name, and the Red List would still give a single comfortable verdict on a group one of whose species may be extinct.

• Németh et al. 2024, the revision of the European blind mole-rats

  The taxonomy that makes these eight pages possible. In Molecular Phylogenetics and Evolution 190: 107958, Attila Németh, Edvárd Mizsei, Levente Laczkó, Dávid Czabán, Zsolt Hegyeli, Szabolcs Lengyel, Gábor Csorba and Gábor Sramkó sampled all but three of the twenty-five described forms and, on several genetic markers, arrived at eleven species in three superspecies, six of them within Nannospalax superspecies leucodon. The Mammal Diversity Database follows this revision, and so therefore does this guide: it is the reason N. bulgaricus, N. hellenicus, N. hungaricus, N. insularis, N. montanoserbicus, N. montanosyrmiensis and N. monticola have pages of their own here instead of a line on the Lesser Blind Mole-rat's. The newly described subspecies nopcsai of N. hellenicus comes from the same work.

• Parker et al. 2012, the North American Beaver in Eurasiahet artikel zelf is niet vrij; alleen geciteerd

  The scientific basis behind the status block of the North American Beaver. In Wildlife Biology 18(4):354–365, Parker, Nummi, Hartman and Rosell set out what the 1937 release in Finland produced, why hybridisation with the Eurasian Beaver is impossible — forty chromosomes against forty-eight — why the two species cannot be separated in the field, and what would be needed to remove the species from Eurasia. That proposed eradication was never carried out, and that fact stands in the guide.

• Paturzo et al. 2025, the expected spread of Finlayson's Squirrel in Italyhet artikel zelf is niet vrij; alleen geciteerd

  The spatial side of the alien story for Callosciurus finlaysonii. In Biological Invasions 27:179, Paturzo, Buglione, Rivieccio, Biondi, De Filippo, Troisi, Gregorio and Fulgione modelled the suitable habitat of the species in Italy, forty years after the southern release, and establish that the suitable area is far larger than what the species now occupies and that its centre of gravity lies in the coastal strip and in settlements. This guide takes from it that the expansion along the Tyrrhenian coast is far from over, and the authors' recommendation that eradication be started now rather than later — the argument set in the status block against the lesson of the Grey Squirrel in Piedmont.

• Red Data Book of Ukraine

  The measurements of the Ukrainian birch mice. The online edition of the Червона книга України gives a description per species with measurements, distribution and status; for Sicista loriger and Sicista severtzovi no western source treats them separately.

• San Diego Zoo Wildlife Alliance Library

  The measurements of the polar bear. The San Diego Zoo Wildlife Alliance library compiles a fact sheet per species from the scientific literature, with the provenance of every figure; for the polar bear female and male are given separately, and so they stand in this guide.

• Sea Watch Foundation

  Measurements for part of the cetaceans. The Sea Watch Foundation is a British research organisation that has counted the cetaceans around the British Isles since the 1970s and publishes a sheet per species with length, weight, distribution and life history. For cetaceans the length is the total length, from snout tip to fluke notch; there is no head-body length as in a land mammal.

• Savić, Ćirović & Bugarski-Stanojević 2017, the chromosomal forms of the blind mole-ratsCC BY

  The chromosome numbers given with every split in this guide. In Genes 8(11): 292, Ivo Savić, Duško Ćirović and Vanja Bugarski-Stanojević set out the life's work of the Serbian karyological school: for each chromosomal form the diploid number 2n, the fundamental number NF and the area it occupies. From it this guide takes 2n = 56/84 for N. leucodon, 48/84 for N. hungaricus, 54/86 for N. montanosyrmiensis, 54/84 for N. monticola, 56/82 for N. montanoserbicus, 58/88 for N. hellenicus and 46 or 48 at NF = 76 for N. bulgaricus, along with the division into four main branches and the finding that crossings between different forms produced no embryos — the reason these forms are now treated as species.

• SECEM, the Spanish mammal atlasde databank zelf is niet vrij; alleen geciteerd

  The Iberian side of Crocidura iculisma, which appears in no handbook because the species still sits under the Lesser White-toothed Shrew there. The Sociedad Española para la Conservación y Estudio de los Mamíferos keeps a page per species in its online atlas, and the page for this shrew gives this guide three things: the fragmented Iberian distribution — eastern Cantabria, the north-west of the peninsula, the Serra de l'Albera, the Sistema Central and the marshes of the Gulf of Cádiz; the difference in habitat between the northern and central populations, in mountain woodland, dense scrub and mixed farmland, and those of Cádiz, in saltmarsh; and the national assessments, with Least Concern in Spain against Endangered in Portugal. The page also names two external tendencies that this guide carries over as tendencies and not as keys: a proportionally longer tail than in the Greater White-toothed Shrew, and dark ears.

• Seifert et al. 2012, skin shedding and tissue regeneration in spiny micealleen geciteerd; de tekst zelf is niet vrij

  The measure of what spiny mice do with their skin. Seifert and co-workers showed in two East African species, Acomys kempi and Acomys percivali, that the skin tears under very slight tension, that the animal loses large flaps of coat in the process, and that the wound closes without scarring; in an ear punch, hair follicles, sebaceous glands, dermis and cartilage were all regenerated. This guide cites it under the Cairo Spiny Mouse, and says there that it was measured in two other species of the same genus and not in that species itself.

• Finnish Association for Nature Conservation

  The measurements of the Saimaa ringed seal. The Finnish Association for Nature Conservation runs the protection of this species and gives the mean total length and the weight from its own work on Lake Saimaa.

• The Mammal Society

  Field measurements for the British species. The Mammal Society is the mammal society of the United Kingdom and gives a fact sheet with measurements and weight for every species.

• The Wildlife Trusts

  Field measurements for the British species, alongside those of the Mammal Society. The Wildlife Trusts are the county conservation charities of the United Kingdom; their species pages give length and weight in rounded form.

• Ultimate Ungulate

  Field measurements for the ungulates, including the shoulder height that the other sources often omit. Ultimate Ungulate is a reference work on the ungulates of the world, kept by Brent Huffman, with the measurements and their sources for every species.

• Dutch Association of Regional Water Authorities, muskrat and coypu managementauteursrechtelijk beschermd; alleen geciteerd

  Why the muskrat in the Netherlands is not a natural phenomenon but a question of flood safety, and what the policy actually is. The Association of Regional Water Authorities explains that muskrats and coypus dig burrows and galleries in dykes and can thereby cause breaches and floods; that in 2019 the water boards decided to push the muskrat back to the national border, the goal being that from 2034 fewer than five hundred animals a year are caught inland; that this goal has already been reached for the coypu; and that the continuing influx from Germany costs more than five million euros a year. This guide takes from it the figures and the policy line in the status blocks of both species.

• Regulation (EU) 1143/2014 on invasive alien speciesHergebruik van EU-wetgeving is toegestaan (Besluit 2011/833/EU); de tekst zelf is niet auteursrechtelijk beschermd

  The legal framework on which the status block of every alien in this guide rests. The Regulation of the European Parliament and of the Council of 22 October 2014 establishes the list of invasive alien species of Union concern and sets out what the list means: for a listed species there is a ban on introduction, keeping, breeding, transport, sale, use, exchange and release, and member states are required to carry out early detection, rapid eradication of new incursions and management of established populations. This guide takes from it the precise wording of those duties, and the reason why for an alien the global Red List status and the European status are two entirely different things.

• WikidataCC0 1.0

  The vernacular names. The Dutch, English and Spanish name of every species were taken from Wikidata, which links names per language to the scientific taxon. Where Wikidata was silent the name was looked up by hand and recorded separately. Wikidata is CC0 and asks for no attribution; it is listed here because the reader should know where the heading of a species page comes from.

• Wikimedia CommonsCC / publiek domein

  All the photographs: the animal itself, the tracks and signs and the habitats. Every file is CC0, public domain, CC BY, CC BY-SA, CC BY-NC or CC BY-NC-SA; licences that forbid adaptations (ND) are not used. The main photograph is always a free-living animal in the field — a camera-trap image counts as a field photograph — and museum material is not used at all: no skulls, no skeletons, no mounted animals. Author, licence and source page are listed per file below.

• WikipediaCC BY-SA 4.0

  Field measurements where none of the other sources gives a figure, and the species accounts against which the name explanations were checked. The measurements come from the English-language species articles and carry that source's uncertainty: a range from the literature, not a single measurement.

• Zannetos et al. 2024, the blind mole-rat of LesvosCC BY 4.0

  Everything this guide can say about the European side of Nannospalax xanthodon. In Life 14(10):1231, Zannetos, Theodorou, Zevgolis, Galinou and Akriotis modelled the suitable habitat of two burrowing rodents on Lesvos and establish in passing that the island's populations form the western edge of the species' entire global range and are its only European populations. The guide further takes from it that the best habitat on Lesvos consists of non-irrigated arable land, pasture and discontinuous urban fabric, that the model puts roughly twenty-two per cent of the island in the suitable class, that suitability falls with altitude, and that the mounds there lie twenty-five to thirty metres apart — the only published figure for this species' mound spacing. The paper is CC BY 4.0.

• Zeehond.org

  The measurements of the harbour seal. Zeehond.org gives a profile per species with measurements, field marks and the state of affairs in the Wadden Sea; here too the length is the total length, snout to hind-flipper tip.

• Zodion — the species accounts of the Zoogdiervereniging

  The species accounts from which the measurements under the key Zoogdiervereniging are taken. Zodion is the species platform of the Dutch Mammal Society and gives for each species head-body length, tail length and weight, along with habitat, food, breeding and field signs. For the harvest mouse, the brown rat and the black rat it also supplies the dimensions of the signs themselves — the droppings, the fore and hind prints and the diameter of the burrows — and the Dutch Red List status of 2020.

• Zoogalaktika

  The measurements of the great jerboa, alongside those of cicon.ru. Zoogalaktika is a Russian educational nature portal with species accounts drawn from the Russian-language literature.

• Zoogdiervereniging (Dutch Mammal Society)

  Field measurements for the species that occur in the Low Countries. The Zoogdiervereniging keeps the Dutch mammal records and gives for each species an account with measurements and weight, based on Dutch and Flemish fieldwork. The most used source of head-body and tail length in this guide.

• 'Amerikaanse rode eekhoorn, een veel geziene exoot', Exoten 2022auteursrechtelijk beschermd; vrij te raadplegen via Natuurtijdschriften, alleen geciteerd

  Everything this guide says about the American Red Squirrel in the Netherlands. The article in the journal Exoten describes the run of records since about 2011, concentrated in the Randstad; that they almost always concern single escaped or released animals with no follow-up; that a peak year such as 2020 is owed largely to one animal in Almere; and the two exceptions that do matter — a nest with young in Gaasterland, Friesland (Oudemirdum) in 2012, with indications of earlier breeding on the spot, and a lactating female in the Kralingse Bos at Rotterdam in 2019. Without this article the page would have raw record counts and no story.

• 'Canadian Beavers in the Nordic Countries', NiCHE 2025auteursrechtelijk beschermd; alleen geciteerd

  The figures behind the Finnish beaver story. This overview from the Network in Canadian History & Environment gives the nineteen Norwegian beavers Finland restored in 1935–36, the seven North American beavers released there in 1937, and the position in 1999: some twelve thousand North American against some fifteen hundred Eurasian beavers. It also gives the difference in chromosome number and the fact that Sweden deliberately chose the Eurasian species for its own reintroduction. This guide takes the figures on the North American Beaver page from it.

• 'Eastern grey squirrels in Europe', WikipediaCC BY-SA 4.0

  The introduction history of the Grey Squirrel in Europe, with the dates and places that stand in the page: the first concerted release in England in 1876 and the run of releases that followed until the 1937 ban; the twelve animals Lord Longford let go at Castle Forbes in Ireland in 1911; and the three Italian nuclei — Stupinigi near Turin in 1948, the parks of Nervi near Genoa in 1966 and Trecate in 1994. The article also gives the part played by squirrelpox virus in the displacement of the Red Squirrel and the failed eradication in Piedmont, begun in 1991 and halted by litigation.

• Jarman & Calaby 2008, in Van Dyck & Strahan (eds.), Mammals of Australia

  The head-body length of the red-necked wallaby (66–92 cm), from the species chapter in the standard reference Mammals of Australia (3rd ed., 2008).

• Kryštufek et al. 2018, the description of <em>Talpa martinorum</em>

  The measurements of Talpa martinorum. In Bonn zoological Bulletin 67(1): 41–57, Kryštufek, Nedyalkov, Astrin and Hutterer described the mole of Thrace as a new species. This guide takes the measurements of the eight paratypes: head-body 124–134 mm, tail 24–32 mm and weight 52.5–65 g.

• Habitats Directive (Directive 92/43/EEC), consolidated textHergebruik van EU-wetgeving is toegestaan (Besluit 2011/833/EU); de tekst zelf is niet auteursrechtelijk beschermd

  The annexes to which the status blocks refer. Among the bats, Annex II lists the five European horseshoe bats, the Barbastelle, Schreibers's Long-fingered Bat and, of the genus Myotis, Bechstein's Bat, the Lesser Mouse-eared Bat, Long-fingered Bat, Pond Bat, Geoffroy's Bat and the Greater Mouse-eared Bat; Annex IV covers all Microchiroptera. For species split after 1992 the guide follows the European Commission: its introduction to the revised checklists for Article 17 reporting states that Myotis punicus, formerly included in the Greater and Lesser Mouse-eared Bats, counts as an Annex II and IV species.

• NAMMCO

  Weight of the fin whale. NAMMCO (the North Atlantic Marine Mammal Commission) is the intergovernmental organisation for marine mammal research and management of the North Atlantic states (Faroe Islands, Greenland, Iceland, Norway) and publishes a data sheet per species. For the North Atlantic subspecies of the fin whale that sheet gives a weight that does match the length used in this guide — unlike the figure used earlier, which belonged to the much larger southern subspecies.

One reservation about the measurements, set down here because it concerns the reader. This guide's design prescribes COMBINE for the weight, and for the field measurements a single field-guide tradition: Aulagnier et al., Mammals of Europe, North Africa and the Middle East, supplemented by the Handbook of the Mammals of Europe. None of those works could be obtained from this working environment, and not one figure has been taken from them — neither for the field measurements nor for the weight. That is why they are not in the list above: what is not used does not belong there. Every measurement in this guide comes from the sources that are listed, several traditions side by side, each with its own way of measuring and its own sample; every measurement states which. Two species are for that reason not yet straightforwardly comparable. The measurements will be redone as soon as the prescribed works are at hand. Where a measurement carries two names separated by a slash, the figure was taken from both sources; where something stands in brackets after it — a subspecies, an older name, or “total length, snout to hind-flipper tip” — that says where or how it was measured.

Readers' photographs

Anyone with a photograph of their own of a free-living wild mammal — or of a sign it left behind — that the guide still lacks can submit it under a Creative Commons licence. The rules and the form are on a page of their own. Submit a photograph

Which mammals are in the guide

The map decides the guide. The window runs from the Azores to beyond the Bosphorus and from northern Norway to the northern edge of the Sahara, and that edge is the edge of the list as well: a species that occurs only outside it is not here.

Included is every wild-living mammal for which the Mammal Diversity Database names a country inside the window and which, according to GBIF, has genuinely been recorded inside it. Being rare is no reason to leave a species out.

Seals and the walrus have been in the guide since 7 September 2026 — they come ashore, on coast and pack ice, where they can be seen and identified. Since 26 September 2026 twelve cetaceans have been in the guide too, species regularly seen from the coast — harbour porpoise, bottlenose dolphin, killer whale and nine others. A species found only in the open sea, rarely or never visible from land, is left out: it asks for a different map window and a different guide. For the animals of the pack ice, Svalbard and Bjørnøya appear as an inset in the corner of the map, because the heart of their range lies above the top edge of the map window.

Established introductions with a settled population are included and marked as such. Feral domestic animals are not: the feral cat has been taken off the list again. The rabbit, the house mouse and the black rat are here, but as wild species with a range of their own, not as domestic forms.

Eight countries lie only half inside the window — Russia, Turkey, Kazakhstan, Iran, Iraq, Egypt, Libya and Algeria. The Mammal Diversity Database names the country, but the species may sit in Siberia, in Anatolia east of 37°E or in the Sahara south of 29°N. There the records decide: at least twenty inside the window over the past twenty years. For the border regions themselves — the Maghreb, the Levant and Macaronesia — the same rule applies as in the bird guide: what occurs there annually is included, nothing exceptional beyond that.

The count is an aid to the decision, not an official tally: GBIF is far better filled in north-western Europe than in the south-east, and a nocturnal animal simply generates fewer records than a bird at a feeder.

Measurements: weight and the field measurements

The measurements in the summary box do not come from one source, and each measurement states which.

That is not what this guide's design prescribes. It names two works: COMBINE for the weight of every species — machine-assembled and therefore comparable across species, as AVONET is in the bird guide — and for the field measurements a single field-guide tradition: Aulagnier et al., Mammals of Europe, North Africa and the Middle East, supplemented by the Handbook of the Mammals of Europe. Neither could be obtained while these species were compiled, and not a figure has been taken from them — not for the weight either.

What does stand there comes from the sources above: the Handbook of the Mammals of the World through the treatments at Plazi, the Dutch Mammal Society, Animal Diversity Web, Wikipedia, and for a number of species the one source that carries a measured series — a Russian Red Data Book, a Spanish species sheet, a monograph. Several traditions side by side, each with its own way of measuring and its own sample. Two species are for that reason not yet straightforwardly comparable. This guide's check refuses a measurement without a source key, and refuses a key that is not explained above, so that the provenance of every figure can be seen. The measurements will be redone as soon as the two prescribed works are at hand.

• Still to be consulted: Soria, C.D. et al. (2021), COMBINE: a coalesced mammal database of intrinsic and extrinsic traits. Ecology 102(6), e3344. CC BY 4.0. — Aulagnier, S. et al., Mammals of Europe, North Africa and the Middle East. — Hackländer, K. & Zachos, F.E. (eds.), Handbook of the Mammals of Europe, Springer.

The Red List categories

The status in each species’ summary box is the global assessment of the IUCN Red List, as carried by the Mammal Diversity Database — not the European or a national Red List. A species on a national Red List can be “least concern” globally, and the reverse also occurs. On the cards in the overview the code is shown only for species outside the lowest category: were it everywhere, the threatened animal would be the one that no longer stood out. The IUCN assesses every species against fixed criteria: rate of decline, size of range, population size and probability of extinction. The nine categories, from lowest to highest risk:

LC Least Concern

Assessed and not in any of the threatened categories: usually a widespread and numerous species.

NT Near Threatened

Does not currently meet the thresholds for Vulnerable but is close to them, or is expected to meet them in the near future.

VU Vulnerable

High risk of extinction in the wild: for example a decline of 30 percent or more over ten years or three generations, or fewer than ten thousand mature individuals.

EN Endangered

Very high risk: for example a decline of 50 percent or more, or fewer than 2,500 mature individuals.

CR Critically Endangered

Extremely high risk: for example a decline of 80 percent or more, or fewer than 250 mature individuals.

EW Extinct in the Wild

Survives only in captivity or as an introduced population outside its original range.

EX Extinct

There is no reasonable doubt that the last individual has died.

DD Data Deficient

There is too little information on distribution or population to assess the risk.

NE Not Evaluated

Not yet assessed against the criteria.

• IUCN (2012), IUCN Red List Categories and Criteria, version 3.1, second edition. The thresholds below are the outline; the full criteria are in that document.

The scientific name

At the foot of every species page stands the full zoological name: the species name, followed by whoever first described the animal and in what year. Where that author and year stand in brackets, the species has since been moved to a genus other than the one it was described in — the brackets are not a detail but a rule of the code of nomenclature, and the guide observes it.

The guide follows the arrangement and the naming of the Mammal Diversity Database of the American Society of Mammalogists. Author, year, the original name, the type locality and the field that states whether the author belongs in brackets come straight from that edition; this guide's check tests the brackets against it. The type localities have been shortened and rendered in present-day place names.

GBIF, the database behind the distribution maps and the Red List categories, is sometimes behind on naming or follows a different arrangement — Clethrionomys against Myodes for the bank vole is the best known case. Where that is so, the GBIF name stands after it, without further explanation: enough to find the animal again in other sources.

The meaning of the names is explained from the Latin and the Greek, with the species accounts of the English Wikipedia alongside. Some of the species are still waiting for a second check.

• Mammal Diversity Database (2026), version 2.5, American Society of Mammalogists. CC BY 4.0.

Arrangement and sequence

The arrangement and sequence of orders, families, genera and species follow the Mammal Diversity Database of the American Society of Mammalogists, the continuously updated global checklist of the mammals. One source, applied consistently, also where it departs from GBIF: where the MDD follows a recent split that the GBIF backbone does not yet have — Clethrionomys against Myodes for the bank vole — the GBIF name stands after it.

• Mammal Diversity Database v2.5 (ASM)
• Foley et al. 2023, Science 380, eabl8189 (Zoonomia)

Texts

The texts on this site were written for this guide. Factual data on measurements, distribution and status draw on standard field guides and the IUCN Red List.

Typeface

The running text is set in IBM Plex Sans, the headings in Cormorant Garamond and the small labels in IBM Plex Mono — the typefaces of vorstman.com. Only the title of each page is set in Antonio, a narrow, tall grotesque in the spirit of the classic field guide covers. All four are under the SIL Open Font License 1.1 and are served from this site itself, so no request goes to an outside server.

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