Several bird species can produce multiple broods per year.
While some species may use the same nest for the second (third) brood, many birds, e.g., species in the Turdidae family tend to make new nests for the new brood.
Even if the nest site remains unchanged, the lining material is likely replaced due to the parasite load and accumulation of smell, fecal matter and prey remains.
I was wondering if there are differences in the use of nest materials among bird species that produce additional broods during the same breeding season when spring material availability is compared to summer material availability.
I began considering this issue when I realized that most mammals molt after winter.
Thus, for example, animal hair would be unavailable in such quantities when the birds are preparing for their second clutch.
Also, some plants might be reduced in attainability (e.g., mosses on forest floor would be overshaded by taller grasses and forbs and harder to pick and the last season’s straw would have undergone further decay under the influence of the warm weather and the new vegetative growth).
On the other hand, thermal insulation requirements might be slightly reduced later in the season.
It would be highly interesting to study bird nest material choices during the later parts of the breeding season when new broods are expected.
Notes by Ieva 