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Providing evidence to improve practice

Action: Remove/treat endoparasites and diseases Bird Conservation

Key messages

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  • Three studies from across the world investigating a range of taxa and parasites found that birds had higher productivity or survival if either chicks or adults were treated for endoparasites.
  • One small study from Spain found no effect of Staphylococcus aureus treatment on eagle survival, while a study from Mauritius found uncertain evidence as to whether trichomoniasis treatment increased survival of pink pigeons Nesoenas mayeri after fledging.
  • A randomised, replicated and controlled trial from the Netherlands found lower parasite burdens but also lower survival in Eurasian oystercatcher Haematopus ostralegus chicks treated with anthelmintic drugs.


Supporting evidence from individual studies


A small study in 1976-88  in the wetlands of the Doñana National Park, Spain (Ferrer & Hiraldo 1991) found that survival rates of Spanish imperial eagle Aquila adalberti chicks did not appear to be affected by treating them for Staphylococcus aureus infections (two of 19 untreated chicks died, probably from infections vs. none of the nine treated chicks died before fledging). The authors note that this may be due to the small sample size in the study. This study also discusses other interventions, in ‘Add perches to electricity pylons to reduce electrocution’, ‘Bury or isolate power lines’, ‘Use signs and access restrictions to reduce disturbance at nest sites’ and ‘Foster eggs or chicks with wild conspecifics’.



A controlled cross-over experiment during 1996-2000 on two moors in northern England (Newborn & Foster 2002) found that red grouse Lagopus lagopus scoticus in an area provided with quartz grit treated with anthelmintic drugs raised between 38% and 100% more chicks than grouse in a control area (treatment areas: 4.9-7.1 chicks/hen estimated from 36 radio-tagged birds and 4.9-6.7 chicks/hen estimated from 125 birds seen on counts using pointing dogs vs. control areas: 1.9-4.8 chick/hen from 36 tagged birds and 2.8-4.5 chicks/hen from 117 on dog counts) and had significantly lower levels of infection of the parasitic nematode Trichostrongylus tenuis (34% fewer worms over five years). This was despite the fact that the medicated areas did not have larger broods or higher hatching success (medicated areas: 9.6 eggs/clutch, 90% hatching success for 161 clutches; control areas: 9.4 eggs/clutches, 94% hatching rate for 153 clutches). Survival rates of adults did not vary between medicated and control areas.



A randomised, replicated and controlled trial in 1996 on an island in the northern Netherlands (Van Oers et al. 2002) found that fledging success of Eurasian oystercatcher Haematopus ostralegus broods was significantly lower when chicks were treated with anthelminthic drugs, compared to controls (18-20% success for treated broods vs. 29-38% for controls). This was despite there being no significant differences in clutch size or hatching success between groups and treated hatchlings having significantly lower incidence of gut parasites (41% of 17 treated chicks infected vs. 60% of 20 untreated chicks). The authors suggest that interference with chicks’ immune systems could have driven this pattern.



A controlled, replicated study from 1992-1999 on Ile aux Aigrettes, Mauritius (Swinnerton et al. 2005) found that pink pigeon Nesoenas mayeri (formerly Columba mayeri) chicks with suspected trichomoniasis Trichomonas gallinae had significantly higher survival if treated with carnidazole compared with untreated chicks showing symptoms (54% survival for 89 treated chicks vs. 0% survival for 19 untreated). Across both symptomatic and asymptomatic chicks, treated chicks had higher survival rates than untreated chicks (62% survival of 129 treated vs. 27% of 123 untreated). However, treatment did not affect subsequent juvenile survival up to 150 days old. Across sites on both the island and mainland Mauritius, survival of treated birds (both juveniles and adults) was significantly higher than untreated birds (74% survival of 19 treated birds vs. 25% survival for 24 untreated). Providing medicated water to all individuals on Ile aux Aigrettes did not reduce the incidence of trichononiasis in the subpopulation, with birds becoming re-infected after treatment stopped.



A randomised, replicated and controlled experiment in wetlands in Manitoba, Canada (Amundson & Arnold 2010) found that survival of 322 American coot Fulica americana chicks was higher in 2004, when they were treated with fenbendazole (an anthelmintic drug), compared to untreated chicks (51% survival to 40 days for treated chicks vs. 39% for untreated chicks). In 2005, survival of 340 chicks was again increased by treatment, but chicks with parents that were treated whilst incubating also had higher survival rates, despite there being no detectable change in parasite burden in adult birds (58% if both parents and chicks treated; 46% if only chicks treated; 45% if only parents treated vs. 33% if neither treated).


Referenced papers

Please cite as:

Williams, D.R., Child, M.F., Dicks, L.V., Ockendon, N., Pople, R.G., Showler, D.A., Walsh, J.C., zu Ermgassen, E.K.H.J. & Sutherland, W.J. (2019) Bird Conservation. Pages 141-290 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2019. Open Book Publishers, Cambridge, UK.