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If Dinosaurs Could Fly
> The only true insulatory feathers are the degenerate ( lacking
>derived barblets) of ratites and flightless birds. Down is not an
>effective insulator in wet conditions. One of the main causes of infant
>mortality in juvenile birds is when the down feathers get wet and they
>die of hypothermia. Pretty maladaptive.
Would down be maladaptive if water-shedding flight feathers evolved first?
In that case, selection might operate to provide adults with thermal long
johns to go under the raincoat, at the expense of a few chicks. Hard to say
a priori where that adaptive balance might lie.