Sources & licences

This guide is built on public sources and on media under a Creative Commons licence or in the public domain. Below, first where the data come from — the species list, the tree of life, the measurements, the habitats and the range maps — and then the full list of photographs, with the author, the licence and the source page for every file. Nothing is used under a no-derivatives (ND) licence.

Where the data come from

The guide rests on a handful of public data sources. They are gathered here, with what they supply and on what terms.

• AviListCC BY 4.0

  The sequence and arrangement of orders, families, genera and species, and the Red List category. AviList is the global checklist that the major lists — the IOC list, Clements and BirdLife — have maintained together since 2025, so that there is one list instead of three. This guide follows version 2025b.

• B10K and the PhyloCode

  The clades above the rank of order, which appear in the tree and in the side menu. They follow the family-genome tree of the Bird 10,000 Genomes project (Stiller et al. 2024) and carry names established under the PhyloCode — a naming that labels a branch of the tree rather than a rank.

• AVONETCC BY 4.0

  The wing length and the mass of every species. Eleven measured traits of all 11,009 bird species in the world, built from measurements of 90,020 individual birds in museums and in the field (Tobias et al. 2022). One source for every species, so that two birds in this guide really can be compared.

• USNVC and CNVC

  The habitats on land. The U.S. National Vegetation Classification arranges vegetation from Formation Class down to Association; Canada describes its vegetation with the same upper hierarchy, so that one vocabulary covers the United States and Canada, and through the international IVC also Mexico. This guide uses the top two levels: ten main groups and forty-four formations.

• CMECS

  The habitats at sea and on the coast. The USNVC covers vegetation only and itself refers onward to the Coastal and Marine Ecological Classification Standard for the salt part. The groups Sea and Coast come from there.

• GBIFCC BY 4.0

  The density on the range map. GBIF gathers records from museums, ringing stations and observer networks into one searchable whole. For North America the great majority arrives through eBird.

• Natural Earthpublic domain

  The country outlines, the national borders and the boundaries of states, provinces and Mexican states on which the range map is drawn.

• Wikimedia CommonsCreative Commons and public domain

  Every photograph of the birds and of the habitats. Each file carries CC0, public domain, CC BY, CC BY-SA, CC BY-NC or CC BY-NC-SA; ND licences are not admitted. Author, licence and source page are listed per file below.

• UnsplashUnsplash licence

  The photograph on the front page: a male Northern Cardinal in a snowy wood, taken by Jason Krieger. It is the only photograph in the guide that does not carry a Creative Commons licence. The Unsplash licence permits free use, commercial use included, and asks for no attribution; it is credited here anyway, as every other photograph is.

Readers' photographs

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

Which birds are included

The map decides the guide. The window runs from the Aleutians to eastern Greenland and from northern Greenland to the southern border of Mexico, and that window is also the edge of the list: a bird that occurs only outside it is not here.

The guide covers Canada, the United States and Greenland. Of those it includes everything that occurs annually — breeders, winterers and passage migrants, however scarce — plus vagrants with more than ten accepted records. Below that limit a bird belongs in a work of reference, not in a guide you take into the field.

Mexico follows in a later round. It is already on the map, because a window that changes later means every map has to be drawn again. The Caribbean islands and Central America appear as land because a map is a rectangle, but their birds are not in the guide. Where a North American migrant winters there, the map does colour it.

At the moment 904 of the 904 species on the list have been written up, with a page for every order and every family. The rest will follow.

Measurements: wing, wingspan and weight

The wing length and the mass in the panel beside each bird come from one source: AVONET. The wing length is the ringer's measurement: from the carpal joint — the bend halfway along the wing — to the tip of the longest primary. The mass is the mean of the birds weighed; a bird's weight varies greatly through the year, so a single figure says more here than a range from another source.

The length of the bird does not come from AVONET but from the field guides. This guide follows All About Birds of the Cornell Lab of Ornithology, the same tradition for every species. Handbooks measure differently — measuring skins gives systematically higher figures than writing a field guide — and a single value from another tradition wrecks the proportions between species.

The wingspan is not in AVONET, nor in any other series of measurements: it is hardly ever taken from a living bird, and the figures in the handbooks are themselves estimates that differ from book to book. This guide therefore estimates it from the measured wing length, using a ratio that differs by family — in a swift, which is almost all hand, the wingspan is 2.6 times the wing length; in a grebe, with its long arm, 4.5 times. Those ratios are calibrated on the published wingspans of 581 species in the European guide; a check in which each species is left out of its own calibration gives a median deviation of four per cent, with four in five species within ten per cent. Three orders Europe does not have — the New World vultures, the tropicbirds and the trogons — borrow their ratio from a group built the same way. Hence the c.: it is a well-founded estimate, not a measurement.

• Tobias, J.A. et al. (2022), AVONET: morphological, ecological and geographical data for all birds. Ecology Letters 25, 581–597. CC BY 4.0.

The Red List categories

The status in each species' summary box is the global assessment of the IUCN Red List, as carried by AviList — not a North American or national list. A species listed under Canada's Species at Risk Act or the Endangered Species Act in the United States 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 bird 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 above are the outline; the full criteria are in that document.

The range map

The map has two layers of different origin, and that difference matters enough to state here.

Which seasonal colour a state, province or country receives — resident, breeding, winter or passage — is a judgement about the species. How dark that colour is comes from GBIF records for 2006–2026: counted per 0.7° cell, divided by all bird records in that same cell, and averaged per unit. That division is needed because GBIF counts observers, not birds: without it the map is a map of where birdwatchers live.

The GBIF map service has no month filter. The count is therefore year-round and cannot find the seasons by itself; the seasonal division is set by hand. That is the largest reservation attached to these maps.

The map unit is the state or province, not the country: on a map of North America one colour for the whole of Canada says nothing. There are 122 drawable units. The projection is Lambert azimuthal equal-area about 100°W and 50°N.

A species that occupies only a small part of the window gets its own zoomed map, with its own country outlines. That is always a crop of the standard frame and never a look beyond it: land that is not visible on the standard map does not appear on a zoomed one either. A species confined to Hawaii thus automatically gets a map of Hawaii alone.

The habitats

Every species is tied to the habitats where it actually rests and feeds, at most five. Ten main groups from sea to city, with forty-four formations below them.

The arrangement on land follows the USNVC, shared by the United States and Canada; sea and coast come from CMECS, and farmland, garden and built-up land from the cultural branch of the USNVC. The CEC ecoregions and the Bird Conservation Regions are deliberately not used here: those are places on the map and not habitats a bird sits in — the range map already answers that question.

The scientific name

At the foot of every species page stands the full zoological name line: the species name, followed by who first described the bird and in which year. If that author and year stand in parentheses, the species has since been placed in a genus other than the one it was described in — the parentheses are not a detail but a requirement of the code of nomenclature.

Genus, species and subspecies are italic; the author, the year and the words subsp. and var. are not. The genus is written out in full at first mention and only abbreviated after that. The guide's verification program tests those rules at every delivery.

The guide follows the arrangement and the naming of AviList. Author, year, the original name and the type locality come from its extended edition. The meaning of the names comes largely from the species accounts of the English Wikipedia, and there above all from the passages that cite Jobling.

• AviList Core Team (2025), AviList: The Global Avian Checklist, version 2025b, extended edition. — Jobling, J.A., The Helm Dictionary of Scientific Bird Names, cited through the species accounts of Wikipedia. — Dauncey, E.A. et al. (2016), Common mistakes when using plant names and how to avoid them. Eur J Integr Med 8(5), 597–601.

Arrangement and sequence

The sequence and arrangement of orders, families, genera and species follow AviList. Above the rank of order stand clades: these follow the family-genome tree of the B10K project and carry names from the PhyloCode.

• AviList v2025b
• Stiller et al. 2024, Nature 629, 851–860 (B10K)

Texts

The texts on this site were written for this guide, equally in all three languages. Factual data on measurements, range and status trace back to the sources above.

Typeface

The running text is set in IBM Plex Sans, the headings in Cormorant Garamond and the small labels in IBM Plex Mono — the letters of vorstman.com. Only the title of each page is set in Antonio. All four are freely available under the SIL Open Font License.