A Sparrowhawk Accipiter nisus with multiple health problems

In mid-April 2023, a dead female adult sparrowhawk (Accipiter nisus) in poor body condition was submitted to the DWHC for pathological investigation.

Investigations showed that the sparrowhawk died from suffocation due to widespread inflammation in the mouth, windpipe, lungs and air-sacs. The inflammation was caused by a combination infection with two parasites (Trichomonas sp. and Eucoleus dispar) and a secondary bacterial infection. The bird tested positive for highly pathogenic avian influenza. Additional findings included poor mineralisation (of the skeleton) and gastrointestinal hemorrhage which typically occurs as a result of reduced or insufficient food intake over several days. In this case it is likely that the oral inflammation led to both impaired food intake and increased energy expenditure.

The cause of the poor mineralisation, that leads to skeletal weakness, was not determined. One possible reason for this is related to acid rain resulting in amino acid deficiencies (https://edepot.wur.nl/418194 (in Dutch)). In female birds, amino acids needed for egg production are then recruited from the bones (https://www.natuurkennis.nl/Uploaded_files/Publicaties/verzuring-van-loofbossen-op-droge-zandgronden-en-herstelmogelijkheden-door-steenmeeltoediening.7425e1.pdf (in Dutch)).

Whether or not the infection with the highly pathogenic variant of avian influenza (H5N1) was clinically relevant is unclear: the absence of neurologic abnormalities suggests that either the bird was very recently infected or that the infection was asymptomatic.

Sparrowhaws in the Nijmegen region

The sparrowhawk population in the woods of Nijmegen, which includes the ‘Groesbeekse bos’ where this bird was found, has decreased dramatically since the turn of the century. This is possibly due to an increase in predation by hawks and an increase in chick deaths which has also been observed. This latter is often attributed to Trichomonas infection though it has not been definitively proven that this is not caused by a parasitic infection with Eucoleus dispar (https://dwhc.nl/en/2023/03/eucoleus-dispar-found-in-eurasian-sparrowhawks/). Interestingly, sparrowhawks that nest in or near villages often have improved chick survival rates possibly linked to increased food availability and reduced predation in these areas. As part of their research into the prevalence of zoonoses and avian flu, the NIOO-vogeltrekstation have been routinely sampling bird of prey nestlings since 2023. It is hoped that this research will reveal the extent of infections such as avian flu in these species.

Thanks to Gerard Müskens for information regarding sparrowhawks in this region.