The bottom of a Highland loch could hold clues to the breeding habits of a rare and colourful wild bird.
Slavonian grebe numbers have gone down
The Royal Society for the Protection of Birds (RSPB) Scotland considers Loch Ruthven in Inverness-shire to be the key UK site for the Slavonian grebe.
Layers of sediment will be examined for dead insects to determine whether years when they were in abundance helped the bird rear more chicks.
A total of 39 grebe pairs were counted last year, down from 43 in 2005.
RSPB Scotland said it was among the country's rarest birds and estimated there could be as many as 10 golden eagles and four ospreys for every Slavonian grebe in Scotland.
The bird first nested in Scotland in 1909 near Loch Ness.
The impact of the weather on the grebe is also being investigated.
RSPB Scotland is inviting the public to take a closer look at the grebe at the loch on 29 April between 1400 and 1700 BST.