Data sources and credits

Where the facts on Birdfact come from, how we process them, and the credit each source asks for.

Where and when birds occur

Our country, nation, county and state bird lists, the months on each species page and the “birds to see this month” lists are built from the EOD – eBird Observation Dataset (Cornell Lab of Ornithology), published on GBIF.org under CC BY 4.0. It holds the records birdwatchers submit to eBird. We download counts of records per area, month and species (2019–2024) and never display individual records. The current build covers 327 published area lists. Last rebuilt 25 September 2026.

How a bird gets on a list

  • Listed: recorded in the area in at least 3 of the 6 years (and, if only 3, in the same month in each of them), with at least 5 records, a best month of at least 1 in 100,000 of all bird records there and, where we know the number of observers (counties, council areas, states and provinces), by at least 2 different people. Birds recorded in 2 years or fewer count as vagrants and are left out.
  • Months: a month is marked when the bird was recorded in that month in at least 3 of the 6 years, and that month's share of all bird records is at least 5% of its best month.
  • Status comes from the shape of the year: birds regularly recorded in both the breeding months (May to July; November to January south of the equator) and the winter months (December to February; June to August in the south) are residents, unless one season is much weaker; birds of only one of those seasons are summer or winter visitors; birds seen mainly in spring and autumn are passage migrants.
  • How common: from the share of all bird records in the area that are this species, in its best month. Common is at least 0.5% (roughly one checklist in ten or more), uncommon at least 0.05%, and rare anything less.
  • Published pages: an area's page is indexed when it has at least 2,000 records and 20 listed species. Thinner areas still show their list, marked as less complete.
Resident
Recorded all year.
Summer visitor
Arrives to breed; scarce or absent in winter.
Winter visitor
Present outside the breeding season.
Passage migrant
Seen mainly in spring and autumn migration.
Scarce
Recorded in some years but not every year.
Records withheld
eBird withholds many records of this sensitive species, so no months are shown.
Common
Among the most-recorded birds in its best month.
Uncommon
Recorded regularly, but on a minority of outings.
Rare
Few records, even in its best month.

What to bear in mind

  • The lists include only birds that have a Birdfact species guide, so they are not complete checklists: the number on a list is the number of our guides that apply there, not the number of species in the area. The gap is small for Britain and Ireland and larger elsewhere, especially in the tropics.
  • The records show where and when birdwatchers go as well as where birds are. Popular sites and weekends are over-represented, and some areas have few records; those lists are marked as less complete.
  • eBird withholds records of some sensitive species (for example Dartford Warbler, Goshawk and Capercaillie in Britain) to protect them. We list them nationally without months, and never by county.
  • Species names follow our species pages. A few records that the dataset groups differently from our pages are handled with fixed rules: for example, Willow Grouse records from Britain and Ireland count as Red Grouse, and nowhere else.

Citation

EOD – eBird Observation Dataset. Cornell Lab of Ornithology. https://doi.org/10.15468/aomfnb, accessed via GBIF.org. GBIF.org occurrence downloads https://doi.org/10.15468/dl.977w84, https://doi.org/10.15468/dl.7eup5f, https://doi.org/10.15468/dl.4bs4rv, https://doi.org/10.15468/dl.5rrxn3, https://doi.org/10.15468/dl.gwccxe, https://doi.org/10.15468/dl.4y5m5f, https://doi.org/10.15468/dl.3ggph5. Licensed CC BY 4.0; records from 2019–2024, aggregated and filtered by Birdfact.

The GBIF downloads used in the current lists, each with its own DOI:

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