Scottish Dippers Often Bigamists
Abstract from Bird Study
1st June 1996
Male Scottish Dippers are the most macho in the World. In a detailed and long-term study of Dipper, just published in Bird Study, 43: 108-118, amazing numbers of them had two wives - and a few even had three!
This sort of behaviour is well known in the bird world but there have only been a scattered records in Europe and North America of it happening amongst Dippers.
This study was of birds on the River Esk, which flows into the Firth of Forth, and the fieldwork was undertaken over more than 10 years by members of the Lothian Ringing Group. Jeremy Wilson, who wrote the report, was amazed when he realised that they were finding up to 25% of their males with extra females. He scoured the scientific literature and could only find scattered records among the many Dipper studies.
These male birds are really working hard for both their females are raising young at the same time. The primary females are just as successful as in monogamous matings - secondary females raise about 75% the number of young as those who do not have to share their males. For the male Dippers there is an obvious advantage - they are able to raise more young with two females than with one. For the females there was no cost for the primary bird but for the secondary female it might have been the only way they were able to gain access to the really good stretches of water. These are annexed by the male birds in the spring.