In the vicinity of Palmer Station, Antarctica, the seabird tick, Ixodesuriae, forms large aggregations under rocks at the periphery of Adelie penguin rookeries. When the adult penguins return to the rookeries at the beginning of the nesting season the ticks leave their off-host aggregation site, attach to the penguins for a period of feeding, and then subsequently return to the aggregation site. In this study, we searched for chemical cues that may be used by the ticks to locate their aggregation sites as well as cues involved in finding penguins. Tick excreta and soil extracts from beneath tick aggregations contained a pheromone that elicited assembly behavior in unfed larvae, non-fed nymphs and non-fed adults. Guanine, the major excretory product of ticks, elicited assembly behavior, thus, guanine is likely an active component involved in assembly. Non-fed stages also responded positively to penguin guano and uric acid, the primary excretory product of penguins, suggesting that uric acid and other components of penguin guano function as a kairomone used by the non-fed ticks to locate their host. After feeding, the immature ticks’ response to both the assembly and kairomones is switched off for several days, and the ticks regain responsiveness only after they have molted. Fed adult females lay eggs and die without ever regaining responsiveness. Thus, I. uriae relies on two closely related chemicals to regulate two critical aspects of its life: assembly and host-finding. Guanine and other components of tick excreta function as an assembly pheromone in promoting the formation of off-host aggregations, while uric acid and other components of penguin guano function as a kairomone used by the tick to locate its host.