Why weavers may build two or more nests below each other
Nest building and acceptance by females
Many weavers are polygynous, meaning that the male wants to try and attract several females to his colony. The down side is that the male needs to build several nests, and nest building is energetically costly. It takes a weaver at least a day to build a typical nest, but he still continues adding material for a few days at a slower pace. When females come to investigate nests, the male displays mainly from the newest nest. Females usually only accept green nests, ie. built within the last few days as the material soon fades to brown. If a female accepts a nest, she will lay eggs and continue breeding even though the nest will fade to brown. If a female is not interested in a male or his nests, she simply moves on to another colony or male.
Breaking down nests
All this means that after building a nest, a male has a window of a few days to get a female to like it. After that the nest is wasted. So the male breaks down brown nests in his prime spots so that he can build a new green nest and try all over again. This cycle continues through the breeding season.
Double or multiple nests below each other
To break down a nest does not require too much energy, and a male usually breaks it down in 20-30 minutes (in between other activities). Sometimes, however, males don’t bother to even spend the tiny bit of energy to break down a nest, but simply start building the next nest under an old brown one.
Weavers that may build nests below each other
Baya Weaver Ploceus philippinus
Lesser Masked Weaver Ploceus intermedius
Cape Weaver Ploceus capensis
Southern Masked Weaver Ploceus velatus
Red-headed Weaver Anaplectes rubriceps
Grey-headed Social-weaver Pseudonigrita arnaudi
Sakalava Weaver Ploceus sakalava
Village Weaver Ploceus cucullatus
Eastern Golden Weaver Ploceus subaureus
Spectacled Weaver Ploceus ocularis
Sao Tome Weaver Ploceus sanctithomae
Red-billed Quelea Quelea quelea
Thick-billed Weaver Amblyospiza albifrons
Sociable Weaver Philetairus socius
Submit your photo of multiple nests!
If you have a photo of a double (or more) decker nest, please submit it PHOWN, PHOtos of Weaver Nests, is a Virtual Museum, citizen science project at the University of Cape Town, to collect and monitor breeding distributions and colony sizes of weaver birds globally. To take part, register and upload records at Virtual Museum (read the “How to” pdf for help).