Cainism may actually help restore eagle numbers in Ireland

Eagles can’t afford to raise two siblings here and so a form of siblicide observed in youngsters may ironically help Irish restoration

In four out of five golden eagle nests, the firstborn kills, and eats, its little brother or sister. Attacks cease only when the chicks’ feathers begin growing.

And it came to pass, when they were in the field, that Cain rose up against Abel his brother and slew him - Genesis 4.

The golden eagle, symbol of strength and nobility, has a dark side. Two eggs are laid in the huge nest, with a three or four day interval between them. Incubation begins with the first egg, which means that it hatches earlier than the second one. In four out of five nests, the firstborn kills, and eats, its little brother or sister. Attacks cease only when the chicks’ feathers begin growing.

Nine eagle species engage in ‘this apparently inexplicable biological waste’. But why do they behave so barbarously? Food shortages can’t account for it; ‘Cainism’ occurs in the midst of plenty.

Fledging two youngsters may be feasible, but raising a second chick puts additional strain on parents’ resources, increasing the risk that neither chick will survive. Eggs are vulnerable to damage. Infertile ones won’t hatch. Having a second string to their bow provides insurance to parents.

A golden eagle doesn’t breed until it is three or four years old. Given the risks young eagles face, raising two youngsters rather than one is precarious. However, the ‘Cain and Able syndrome’ seems unlikely to greatly enhance the species’ overall survival prospects.

Changing attitudes

Golden eagles were persecuted to extinction in England and Wales. Only in Scotland have they managed to cling on to life. Shooting, poisoning, sheep-dipping and egg collecting are blamed. But times have changed; a more positive attitude towards birds of prey now prevails. The Scottish eagle population, at around 440 pairs, has been relatively stable since the 1980s.

Golden eagles have been extinct in Ireland since 1912, apart from a single nest at Fair Head in 1960. As in England and Wales, shooting and poisoning are blamed for the demise. Picture: RSPB/PA.

But ‘iolair buidhe’ numbers have not recovered in the south of Scotland. However, according to press reports, things are ‘looking up’. In 2018, eagles were relocated from the Highlands to the Moffat Hills in the Southern Uplands. They are thriving there. Over 50 pairs were recorded in 2023, raising hopes that they may colonise the North of England.

The species has been extinct in Ireland since 1912, apart from a single nest at Fair Head in 1960. As in England and Wales, shooting and poisoning are blamed for the demise. Vagrant golden eagles visit Ireland but these avian tourists don’t stay to breed. Re-colonisation in Southern Scotland might change that.

The species needed a boost to help restoration here so, in 2001, six almost fully-grown chicks, were taken from eyries in Wester Ross and released in Donegal. Only nests with two chicks were raided, one chick being taken in each case. I travelled with the team to Scotland. Ringing a chick, I hoped it might help found a new Irish eagle dynasty.

Further importations followed. The youngsters were acclimatised and released in Glenveagh National Park. However, only three pairs were breeding here nine years later. Starvation has been blamed for the poor performance; chicks can’t get enough to eat. Hares and grouse, on which eagles feed their young, are too thin on the ground in a landscape denuded of cover by grazing sheep and deer.

Cain was not ‘his brother’s keeper’ but, ironically, his cruel approach may help Irish restoration; eagles can’t afford to raise two siblings here.