Striped Owl

A striped owl (Asio clamator) grips a tangle of bare twigs at night in Kaa-Iya del Gran Chaco National Park, in southeastern Bolivia. For its size, this owl takes heavy prey. Alejandro Baladrón and María Bó picked apart 126 pellets from a woodland remnant in Buenos Aires Province and found 205 animals, every one of them a vertebrate. Mean prey weight came to 162.7 grams, and animals over 100 grams supplied more than 90 percent of the food by weight: introduced rats, white-eared opossums up to 600 grams, and sixteen Monk Parakeets, the first record of a parrot taken by this species.

Introduced Rattus alone made up 70.7 percent of the biomass in that study, and a 2025 study of a pair in a city park in Cuenca, Ecuador, put the figure at 94.8 percent. It is tempting to call the bird a rat controller. Baladrón and Bó read it differently, as opportunism: rats are abundant in farmland and towns, and no study has yet measured whether owls make any dent in their numbers.