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ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Growth bars (1 Viewer)

Think of growth bars as 'faults' generally casued by a period during which there could be a lack of food for nestlings i.e during prolonged rain etc. As juvenile feathers are generally much weaker and the youngsters are solely reliant on their parents for food whilst in the nest then this lack of food can manifest itself as 'growth bars' - the energy required for growing feathers is diverted elsewhere. So a bird showing growth bars in the tail is probalby a young bird but you shouldn't use this feature in isolation as adults can show similar bar if they've gone through some kind of trauma during moult or have lost their tail through a predator attack.
 
Could someone explain how growth bars are useful for ageing birds?

There's a good description of growth bars in Svensson.

In essence, they are equidistant from the tips of adjacent feathers that have grown simultaneously, as these would in juvenile birds. But adults can grow tails this way also, so it is not diagnostic here. In the secondaries it would be diagnostic, but is hard to see.

They are best used to verify ageing done through other means.
 
As well as Svensson, available from the BTO is Ginn and Melville's 'Moult in Birds' which still provides the best general introductions to feathers and moult. It lays out how a basic knowledge of the main moult strategies aids correct aging (and all found in just the first 25 pages or so).

O.k., no colour pics like Jenni & Winkler, but a helluva lot cheaper! ;) And I think you'll find the chapters I've just mentioned are the standard texts referred to on your upgrade forms making the asking price of £7.50 seem even more of a bargain :t:
 
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