Finding evidence of eccentric moult in historic specimens

As touched on in my previous post about eccentric moult, it seems to be a firmly held belief that
young birds are undergoing a more extensive post-juvenile moult than they used to, and that
this is a result of climate change.

While we are looking closely at the Goldfinches we catch, we cannot know if they are doing
more moult now without first knowing how much they did in the past. To gather data on this, we
are visiting natural history collections to study their specimens and complete moult score cards.

In October, Josh and I visited the National History Museum in Tring. It houses the largest
collection of bird skins in the world, with over 750,000 skins from 8,000 species, representing
95% of all species on Earth. However, we’d gone specifically to look at their collection of 112
British Goldfinches (Carduelis carduelis britannica).

Nearly all of the birds we handled dated from the mid-1800s to mid-1900s. The oldest bird we
studied was from 1824. They had been carefully preserved, some using arsenic and lead, and
so we handled them with extreme care.

Surprisingly, we did find evidence of eccentric moult in two birds! One bird had only replaced
P6, another had replaced P5 and P6. Two other specimens appeared to show evidence of a
descendant moult, though it was difficult to determine the age of the inner primaries given that
the wings had been fixed in a closed position. The best we could say with any accuracy was
that these two birds had moulted P4-P7.

We didn’t expect to find any evidence at all so to find four examples, all from the 1800s, was
quite a surprise. We will continue visiting more collections to increase this data set.

Thank you very much to the curator, Mark, for organising our visit and encouraging us to come
back.

Holly