Pietro Perona, a professor at the California Institute of Technology, is one of the brains behind a pair of smartphone apps that help you do just that: eBird and iNaturalist. But simple as the apps are to use in identifying tens of thousands of species, the science behind them is complex. Gathering enough examples for each species to train a neural network is impossible, so much of Prof. Perona’s work has been focused on making machines more efficient learners, requiring less training data.