Frog choruses of the Sava and Danube floodplains

Fire-bellied toad (Bombina bombina), tree frog (Hyla arborea), marsh and pool frogs, agile and moor frog (blue males in March), green and common toad; Danube crested newt. Lonjsko polje, Kopački rit, Crna Mlaka, Turopolje, Croatia.

Best time: 10 Mar – 25 Mar and 10 Apr – 25 May (March to May). Where: Lonjsko polje – Krapje / Lonja floods, Crna Mlaka fishponds (special ornithological reserve), Kopački rit – Kopačevo channels (Croatia). Time of day: Chorus from dusk, full volume 1–2 h after dark to about midnight.

• You can go on your own
• Free
• No binoculars needed
• Sound 5/5

Open it in the interactive calendarSunrise and sunset listening times for the day you pick, and the map.

When is the best time?

• Peak 1: 10 Mar – 25 Mar — Mid March: moor frog burst (a few days, males blue)
• Peak 2: 10 Apr – 25 May — 10 April to 25 May: fire-bellied toads, tree frogs, marsh frogs

Active from 1 Mar to 30 Jun (March to June) in a typical year.

Time of day

Chorus from dusk, full volume 1–2 h after dark to about midnight; fire-bellied toads also call by day in warm shallows from mid afternoon.

• Night chorus: 30 min after sunset → 00:00
• Warm-afternoon toads: 14:00 → sunset

What will you hear?

Fire-bellied toads' soft 'oop-oop' by the thousand across flooded pasture, tree frog volleys, marsh frog laughter, green toad trills, cuckoo and nightingale at the edges, storks clattering.

Binoculars?

No binoculars needed. Chorus from the dyke and water's edge; a torch for frogs, nothing else.

Where to go

• Lonjsko polje – Krapje / Lonja floods — Flooded pastures in spring; the whole polje croaks. Dyke access. Map
• Crna Mlaka fishponds (special ornithological reserve) — Carp ponds south-west of Zagreb; huge Bombina and Hyla chorus, ferruginous duck, whiskered terns. Access by arrangement with the fish farm. Map
• Kopački rit – Kopačevo channels — Boardwalk and boat at dusk (park programme); Bombina and marsh frogs under the heronries. Map

How to go on your own, and what it costs

Lonjsko polje: the flood dykes at Krapje and Lonja are public at night. Kopački rit: the Kopačevo village edge is free; the boardwalk at dusk is on the park programme. Crna Mlaka: private fishponds — access by arrangement with the fish farm only.

Cost: Free from dykes; Kopački rit entry €3, boat programme €15 adult (2026).

Field-recording notes

Fire-bellied toads are low-level (each call is quiet) but the chorus is spatially enormous — a wide-spaced omni pair on the water's edge works better than any directional rig. Warm still nights after rain; below about 12 °C the chorus stops. Mosquitoes peak exactly then. Fishponds are private: Crna Mlaka has been open to visitors by arrangement, but check current status. All amphibians are protected in Croatia — no netting, no handling.

Sources

• Park prirode Lonjsko polje
• Hrvatsko herpetološko društvo Hyla

Similar spectacles

• Natterjack toad chorusUnited Kingdom · Amphibian chorus · peak 15 Apr–31 MayThe loudest amphibian in Britain — a rolling, ratcheting chorus audible up to 2 km away across dunes.
• Natterjack toad chorus on the Kerry dunesIreland · Amphibian chorus · peak 20 Apr–25 MayA loud, ratcheting 'rrrrRup, rrrrRup' chorus from dozens of males in shallow dune pools — the loudest amphibian in these islands — with the Atlantic surf behind the dunes and snipe overhead.
• Tree frog choruses of Zeeuws-VlaanderenNetherlands · Amphibian chorus · peak 1 May–31 MayA rattling, surprisingly loud 'kè-kè-kè-kè' chorus from hundreds of tree frogs around the old fortress moats and pools — audible across the polder — with marsh frogs and nightingales behind; the ramparts of Retranchement alone hold a few hundred.
• Fire-bellied toads, natterjacks and blue moor frogsGermany · Amphibian chorus · peak 25 Mar–7 Apr and 15 Apr–25 MayFire-bellied toad's melancholy 'uh...uh' by the hundred over shallow pasture ponds, moor frog's bubbling 'waug-waug' underwater chorus, natterjack's ratcheting trill carrying 2 km across dune slacks, tree frogs at full volume, bittern and crane in the background.
• Marsh frog & tree frog chorusesFrance · Amphibian chorus · peak 25 Apr–10 JunWall-to-wall marsh frog laughter from the Camargue ditches, ratcheting tree frogs from Brenne ponds, and natterjacks rolling across the Landes dune slacks.
• Frog nights in the Danube floodplain forestAustria · Amphibian chorus · peak 15 Apr–31 MayTree frog volleys and fire-bellied toads' soft hooting from the oxbows (Altarme), marsh frog laughter, night herons croaking overhead, nightingale and beaver tail-slaps; Danube barges as a slow low bed.

More: all spectacles in Croatia · frog and toad choruses · March · Croatia in April · Croatia in May