Ertholmene: Denmark's only guillemot and razorbill colony
Common guillemot and razorbill (c. 99% of Denmark's breeders on Græsholm), eider, herring and great black-backed gull, grey seals; migrant falls in spring and autumn. Christiansø / Frederiksø / Græsholm, 18 km NE of Bornholm, Denmark.
Best time: 10 May – 30 Jun (May to June). Where: Christiansø (north-west shore facing Græsholm), Græsholm (viewed only), Hammeren, North Bornholm (Denmark). Time of day: The colony from first light (about 04:00 in June) until the day boat arrives at 11:00, and again after it leaves at 15:00 into the evening.
- Partly on your own
- Entry fee
- Telescope recommended
- Sound 4/5
Open it in the interactive calendarSunrise and sunset listening times for the day you pick, and the map.
When is the best time?
Peak: 10 May – 30 Jun. 10 May to end of June
Active from 1 Apr to 20 Jul (April to July) in a typical year.
Time of day
The colony from first light (about 04:00 in June) until the day boat arrives at 11:00, and again after it leaves at 15:00 into the evening.
- Morning colony: 30 min before sunrise → 11:00
- Evening colony: 15:00 → sunset
What will you hear?
Guillemots' growling and razorbills' rattle from Græsholm's rocks 100 m across the sound, eider crooning, gull colonies, the Baltic; at night on Christiansø, migrants and the fortress silence.
Binoculars?
Telescope recommended. The auk colony is on Græsholm 100–150 m across the sound from Christiansø; a scope shows the ledges, binoculars minimum.
Where to go
- Christiansø (north-west shore facing Græsholm) — Fortress island with a guesthouse; day boat from Gudhjem (Bornholm); Græsholm itself is a closed sanctuary. Map
- Græsholm (viewed only) — Bird sanctuary — landing prohibited; the auk cliffs face Christiansø. Map
- Hammeren, North Bornholm — Small new colonies of razorbills on the granite cliffs; walk-in. Map
How to go on your own, and what it costs
Day boat from Gudhjem (Bornholm) — stay overnight in the Christiansø guesthouse or camping area to have the colony before 11:00 and after 15:00; Græsholm itself is closed. Hammeren (north Bornholm): free walk-in razorbill colonies on the granite cliffs.
Cost: Day-boat return fare and island accommodation (check current prices); Hammeren free.
Free or no-guide alternative: Hammeren on north Bornholm: free coastal path from Hammerhavn or Sandvig to small razorbill colonies on the cliffs — no boat, no ticket.
Field-recording notes
Græsholm is strictly closed; the colony is recorded from Christiansø across a 100–150 m sound — a parabolic or long shotgun from the rocks at 04:00, before the day boat arrives (11:00) and after it leaves (15:00). Staying overnight (guesthouse or the camping area) is the whole trick: 100 inhabitants, no cars, no aircraft. Wind exposure is total; pick the lee shore. Eiders nest under every bush on Christiansø — stay on paths in May–June.
Sources
Similar spectacles
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Helgoland Lummenfelsen: guillemots, gannets and the 'Lummensprung'Germany's only seabird cliff: guillemot growls, kittiwake screaming, gannet colony grating, fulmar cackles; at the jump, chicks peeping and adults calling them down to the sea 40 m below.
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More: all spectacles in Denmark · guillemots · seabird colonies · Denmark in May · Denmark in June