Alien rats have impacted native systems worldwide, yet wildlife managers lack techniques to efficiently monitor for rodent invasions where native rodents are present and to control alien rodents sympatric with native rodents. We tested the ability of vertical bait stations to exclude native rodents in the Galapagos Islands, Ecuador. Norway rats (Rattus norvegicus) appeared able to enter all station sizes, whereas black rats (R. rattus) were excluded from larger stations. The endemic rodents Oryzomys bauri and Nesoryzomys narboroughi were unable to enter bait stations of any size, but N. swarthi entered the smallest station. Differences in climbing technique contributed to the advantage of alien rodents over endemic species. Our technique provides wildlife managers in the Galapagos, and potentially other islands with native rodents, a means for early detection and control of alien rats.