Bird Blow Flies, Protocalliphora (Diptera : Calliphoridae), in cavity nests of birds in the boreal forest of Saskatchewan

The frequency of infestation by larval bird blow flies, Protocalliphora, an obligate blood-sucking parasite of nestling birds, in the nests of America n Kestrels (Falco sparverius) was documented in north-central Saskatchewan. We found no evidence of feeding Protocalliphora in 76 intensively monitore d nests. Nesting material from 92 nests was searched for puparia after chic ks had fledged, and only a single P. avium puparium was recovered. We sugge st that Protocalliphora are not important parasites for nestling kestrels i n the boreal forest. Although Protocalliphora were also absent in four Bore al Owl (Aegolius funereus) nests, we did recover P, shannoni from Tree Swal low (Tachycineta bicolor) and House Wren (Troglodytes aedon) nests. These l atter results suggest the absence of Protocalliphora in kestrel nests is pr obably due to species that normally infest kestrels not occurring on our st udy area, as opposed to the genus as a whole being absent. This study is th e first to document P. avium in American Kestrel nests, and expands the kno wn range of P. shannoni.