Richard Collins: German blue tits die from mystery illness

Richard Collins: German blue tits die from mystery illness

Household milk deliveries are back, thanks to the Covid-19 lockdown.

In 1929, a blue tit in Southampton pecked open a bottle-top to get at the cream underneath. Others copied it and, soon, tits all over Britain and Ireland were doing the same. Tackling today’s milk cartons won’t be so easy but a far greater challenge is facing blue tits in Germany; they are dying of a mysterious illness.

The Nature and Biodiversity Conservation Union (NABU) received 13,800 reports of dead and dying blue tits during a 12-day period in April. The west of the country appears to be most affected.

Victims develop breathing difficulties, lethargy and loss of appetite. They don’t fly away when approached. Bodies are often found on the ground below feeders, suggesting that infection spreads where birds congregate. Other tit species are also affected but people are not at risk.

NABU is blaming a bacterium, Suttonella ornithocola, for the outbreak. This lethal pathogen targets the lungs, causing pneumonia. First identified in 2005 in Britain, it was reported from Germany two years ago.

As with the Covid-19 threat, social distancing is recommended for blue tits. Persuading birds to observe the avian equivalent of 2m separation isn’t on, but people in Germany are asked not to put food out for them.

Will this epidemic become a pandemic? Tit behaviour as this time of year may slow the spread of the disease; the flocks that roamed the countryside all winter have broken up and pairs are establishing breeding territories.

Although extra-marital ‘flings’ are relatively common, blue tits are seasonally monogamous with limited social contact between birds, other than partners, in summer.

Territorial self-isolation will cease later in the year, when chicks become independent and head out to seek their fortunes.

According to the Migration Atlas, youngsters seldom travel far; 90% of them are still within 6km of home a month after leaving. Meanwhile, breeding territories abandoned, parents will go their separate ways. Having grown a new set of flight feathers, they will begin gathering into flocks.

Over 2.5m blue tits have been ringed in Britain and Ireland. Ring ‘recoveries’ show that our birds are sedentary; less than 5% were recorded more than 26km from where they were ringed.

None of the hundreds I have ringed over the last 25 years was found more than a few kilometres away.

Blue tits in northern Europe are ‘partial migrants’; many stay at home for the winter while others move to warmer areas in the south. ‘Some of these Scandinavian migrants reach eastern Britain, since these larger brighter-plumaged individuals are not uncommon at east-coast observatories.

There have, however, been remarkably few movements to or from Britain confirmed by ringing’, wrote tit expert Andrew Gosler in the Atlas.

‘Irruptions’ occur from time to time; flocks from northern Europe travel at far as Britain occasionally. There was a ‘tit invasion’ there in 1957, but flocks don’t seem to reach Ireland.

If the blue tit plague spreads in mainland Europe, it could ‘jump’ the channel to England. Thanks to the barrier of the Irish Sea, our Irish birds are ‘cocooned’ and so should avoid the disease.

However, as the Covid-19 experience shows, we shouldn’t underestimate the ability of pathogens to spread.

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