How common is avian hybridization on an individual level?

Hybridization among different bird species is relatively common, but the hybridization rate of individuals is not well known. Justyn et al. use data from the citizen science project eBird to assess the individual hybridization rate in birds, showing that 0.064 % of individuals are hybrids. The accuracy of this new estimate is affected by potential biases introduced by birdwatchers, such as over-reporting of rare hybrids and under-reporting of difficult-to-identify hybrids.