A project undertaken at The University of Melbourne, and supervised by Iliana Medina
Birds’ nests are one of the most marvellous animal structures, but their evolution has remained a mystery for decades. Only in the last years we have started to understand why there are different types of nests and which are the drivers of nest evolution.
Birds have three main nest types: domed nests (with a roof), open cup nests and cavities. Domed nests are the ancestral type of nest in perching birds (passerines). The roof on top of nests was lost through evolution, as species moved to different habitats – most likely less arid places. Scientists suspect that this transition, from domed to open nests, could be important in the evolution of perching birds. First, we know that most living species of birds build open nests, not domed nests. We also know that, at least in Australia, species that build open nests have larger geographic ranges.
Moreover, these species are also less likely to be under risk of extinction compared to species that build domed nests. These pieces of evidence strongly suggest that having an open nest could offer benefits to the lineages that have this trait, which has allowed them to colonise new places and eventually diversify. In evolutionary biology, a trait like this would be called a ‘key innovation’. This hypothesis has never been tested before. We do not know if having an open nest is a key innovation in passerine birds, and which mechanisms could be driving these patterns.
The main aim of this project is to combine macro-evolutionary analyses and field work to reveal whether having open nests is a key evolutionary innovation in birds. It will use field work with Australian species and macroevolutionary analyses to understand the evolutionary and ecological consequences of having this trait. It will showcase Australian fauna to ultimately increase our understanding of the diversity of birds worldwide.
The project involves four different components, combining macroevolutionary analyses and fieldwork.
1. Use macro-evolutionary analyses to test whether species that have open nests have larger geographic ranges and wider climatic niches compared to species with domed and cavity nests. Outcome: This will allow us to test the first expectation of a key innovation, that the trait allows niche expansion.
2. Test whether lineages where species build open nests have higher diversification rates compared to lineages with domed or cavity nests. Outcome: This will allow us to test the second expectation of a key innovation, that it increases diversity.
3. Estimate the energetic costs of nest building in species with open and domed nests, using Australian bird species. Outcome: This aim will give us insights into why having a domed nest has been lost in evolutionary history, and why open nests could be more successful.
4. Compare the evolutionary potential (e.g. variability) in nest structure among different types of nests. Outcome: This aim will test whether open nests are highly flexible structures that can adapt to a wider range of conditions.