Detrimental effects of larval blow files (Protocalliphora azurea) on nestlings and breeding success of Tree Sparrows (Passer montanus)

The effect of bloodsucking parasitic larvae of the blow fly Protocalliphora azurea (Fallen, 1817) (Diptera) on Tree Sparrow, Passer montanus (L., 1758), breeding success was studied in populations breeding in nest boxes in southwestern Slovakia. Out of 52 examined nests only seven broods (13%) were unparasitized. The mean number of larvae per parasitized nest was 22.6 and the total number of parasites per nest ranged from 1 to 80. Large numbers of blow fly larvae and pupae significantly influenced nestling survival and fledging success. In broods with parasite load per chick higher than nine, at least one nestling died. To record the effects of parasites on the body size of nestlings of different ages, nestlings were measured on days 5, 10, and 13 post hatch. First and second broods were analysed separately. A significant negative effect of parasite load per nestling on the body mass, wing length, tarsal length, and tail length of nestlings was found in the second broods only in the 10- and 13-day-old chicks. Tree Sparrow parents did not prolong nestling provisioning time per nestling, as there was no negative relationship between parasite load per nestling and feeding period. Contradictory to most previous studies of the genus Protocalliphora, the present study suggests that these parasites have an important negative impact on the breeding success of the studied Tree Sparrow populations.