Nest-helpers and polyandric trios are known to occur in a few diurnal raptor species (de Vries 1973, Mader 1975, Wiley 1975, Wegner 1976). Among owls, polyandry has been reported in the Barn Owl (Tyto alba) and in Tengmalm’s (Boreal) Owl (Aegolius funereus), while polygyny has been reported in the Common Scops Owl (Otus scops), Snowy Owl (Nyctea scandiaca), Tawny Owl (Strix aluco), and Tengmalm’s Owl (references in Kondratzki and Altmüller 1976).
Because actual genetic investment in the clutch is almost never known in such cases, we use the term helper in the broad sense of another conspecific that assists in the reproductive effort. The helper may be a former offspring of the nesting pair with no direct genetic investment, or a polyandrous female’s or polygynous male’s mate with a variable amount of genetic investment.
Of the two major facets of helping behavior—feeding of young and defense of nest/young—the former would be exceptionally difficult to observe in strigiform birds. This paper reports circumstances, including nest defense, which suggest the presence of a helper at a Long-eared Owl (Asio otus) nest.