Assessing the effects of haematophagous ectoparasites on the health of nestling birds: haematocrit vs haemoglobin levels in House Wrens parasitized by blow fly larvae

Abstract

We compared haematocrits and blood haemoglobin concentrations of nestling House Wrens Troglodytes aedon in nests with relatively large numbers of haematophagous larvae of the blow fly Protocalliphora parorum (>6.4 large larvae/nestling) and nests in which exposure to larvae was severely reduced or eliminated (0–2.0 larvae/nestling). Heavily parasitized nestlings showed no reduction in haematocrit levels but a significant 28% reduction in haemoglobin levels. Previous research on avian response to chronic blood loss suggests that parasitized nestlings may show normal volumes of red blood cells as a result of a rapid production of new cells in response to blood loss and, additionally, as a result of swelling of individual cells left in the bloodstream after parasite feeding. Rapid erythropoiesis places high numbers of haemoglobin‐poor, immature cells into the bloodstream which would explain the reduced haemoglobin levels of parasitized nestlings. Our results refute the conclusion that larval feeding has “little direct effect” on nestling wrens in this parasite–host system, drawn earlier by Johnson and Albrecht (1993) based on examination of haematocrits alone. Our results also strongly suggest that researchers wanting to measure effects of blood‐feeding parasites on birds measure haemoglobin levels, not haematocrits.

Effects ofProtocalliphoraParasites on Nestling Food Composition in Corsican Blue TitsParus caeruleus: Consequences for Nestling Performance

“…This is consistent with results of other studies (e.g. Merino & Potti 1995, O'Brien et al 2001. Hence, the question arises, do parents try to reduce the effects by infestation-dependent feeding and other types of behaviour (Rothschild & Clay 1952, Johnson & Albrecht 1993, Morrison & Johnson 2002, Simon 2003?…”

Ferruginous Pygmy-Owl (Glaucidium brasilianum) and Eastern Screech-Owl (Megascopes asio): New Hosts for Philornis mimicola (Diptera: Muscidae) and Ornithodoros concanensis (Acari: Argasidae)

“…It is unknown if these infestations are affecting nesting success, but effects of parasitic blood loss can include mortality, anemia, and retarded tissue growth due to reductions in hemoglobin levels and transport of oxygen to tissue (O'Conner, 1977;Gold and Dahlsten, 1983;O'Brien et al, 2001). There is no direct evidence that parasitic blood loss had an effect on the survival of these owls.…”

Trade-offs in the early development of tree swallows (Tachycineta bicolor): offspring characteristics, offspring quality, and parental care

“…It is likely that parasitized nestlings that are anaemic have a lower oxygen-carrying capacity, which may result in fledglings having trouble finding food and being more vulnerable to predation in their first few days after leaving the nest due to lowered flight ability and endurance (O'Brien et al 2001;Simon et al 2004). Previous studies have found that nestlings infested with various nest ectoparasites had lower haematocrit values than noninfested nestlings (Chapman 1973;Whitworth & Bennett 1992;Richner et al 1993;Simon et al 2004), although others have found no effect of parasites on haematocrit ( ).…”