Action: Remove ectoparasites from nests to increase survival or reproductive success
- Six of the seven studies that investigated infestation rates found lower rates in nests treated for ectoparasites, one (that used microwaves to treat nests) did not find fewer parasites.
- Two studies from the USA found higher survival or lower abandonment in nests treated for ectoparasites, whilst seven studies from across the world found no differences in survival, fledging rates or productivity between nests treated for ectoparasites and controls.
- Two studies from the USA and the UK found that chicks from nests treated for ectoparasites were in better condition than those from control nests. Four studies found no such effect.
Nestlings are more vulnerable than adults to parasites, so reducing parasite burdens in nests may have a larger impact on reproductive success than treating adults.
Supporting evidence from individual studies
A replicated, controlled experiment during 1987-8 in New York State, USA (Roby et al. 1992) found that survival rates and fledging age of both eastern bluebird Sialis sialis and tree swallow Tachycineta bicolor chicks did not differ significantly between nests where blowflies Protocalliphora spp.were experimentally removed, control nests or nests with blowfly larvae added (bluebirds: 78% survival for removal nests, n = 25 vs. 87% for controls, n = 26; fledging age of 18 days for both treatments; tree swallows: 97% for removal nests, n = 29 vs. 90% for addition nests, n = 30 and 94% for controls, n = 32; fledging ages of 19.4, 19.7 and 19.8 days for removal, addition and control nests respectively). Bluebird nestlings were significantly heavier at 14 days old in removal nests, but the authors note that this was a small change (averages of 28.2 g in removal and 27.0 g in control nests).
A replicated, controlled study in a mixed deciduous woodland in Uppsala, Sweden, in late spring 1988-91 and 1994 (Dufva & Allander 1996), found that great tit Parus major nest boxes from which hen fleas Ceratophyllus gallinae were removed did not have higher hatching or fledging success compared to control nests (83-96% hatching and 69-100% fledging success for 46-47 experimental nests vs. 83-95% and 85-99% for 82-85 controls). In two out of five years, nests treated with pyrethrin had heavier and larger chicks in better condition, but in the remaining three years there were no differences. In another year, treated nests had shorter nestling periods. The authors argue that the impact of fleas is greater in cooler years with higher precipitation.
A replicated, paired site study over two summers in 1991-92 in central Scotland (Alves 1997) found that sand martin Riparia riparia chicks from nests treated with Alugan pesticide (4.25% Bromocyclen) had fewer ectoparasites than chicks from untreated nests and fledged at higher weights (average of 18.8 g for 44 treated nests vs. 18.0 g for 44 control nests; within pairs, chicks from treated nests were heavier in 61% of cases). However, there was no difference in nestling survival between treated and control nests.
A replicated, controlled study from 1982-1989 in Nebraska, USA (Brown & Brown 1999) found that survival of cliff swallow Petrochelidon pyrrhonota chicks from nests treated with Naled (an organophosphate insecticide) did not decline with later laying date, unlike control nests. The number of chicks surviving to ten days old was also higher for fumigated nests than control nests (1.75-2.80 chicks/nest survived to ten days old in 15 fumigated nests vs. a maximum of 2.50 chicks/nest, declining to <1.25 chicks/nest for clutches laid after 25th June for non-fumigated nests).
A small controlled study in 1996 in Corsica, France (Hurtrez-Boussès et al. 2000) found that there were significantly fewer blowfly Protocalliphora spp. larvae on blue tit Parus caeruleus broods that were repeatedly moved to microwave-treated nests (at two, five, seven, nine, twelve and fifteen days old), than in control broods that were not treated (0.2 parasites/chick for six treated broods vs. 15.0 parasites/chick for nine control broods). Fledging weights, survival and other indicators of reproductive success were not reported.
A small randomised, controlled study over three breeding seasons in north-eastern Algeria (Bouslama et al. 2002) found that blue tit Parus caeruleus nests that were heat treated with a microwave (three minutes heating at 830 W) had significantly fewer blowflies Protocalliphora spp. than control (unheated) nests (2.0 flies/nest for ten experimental nests vs. 54.9 flies/nest for eleven controls). Experimental nests also had lower numbers of ticks Ixodes ricinus and hen fleas Ceratophyllus gallinae (8.8 ticks/nest and 3.1 fleas/nest for experimental nests vs. 20.5 ticks/nest and 15.1 fleas/nest for controls), but these differences were not significant after controlling for confounding factors. Growth rates of chicks did not differ between treatments but more chicks fledged from treated nests compared to controls (6.0 chicks/nest vs. 4.6 chicks/nest).
A replicated, controlled study at two brown pelican Pelecanus occidentalis colonies in North Carolina, USA (Norcross & Bolen 2002), found that pelican chicks in nests sprayed with insecticide (1% dilution of Rabon® 50 WP applied three times during the 1998 and 1999 breeding seasons) had significantly fewer immature ticks on them, compared to those in control nests (0.4-4.2ticks/chick in 64 treated nests vs. 10.4–20.1 ticks/chick in 60 control nests). In the first year of the study, significantly more control nests were abandoned than treated nests, but there was no difference in the second study year (1998: none of 30 treated nests abandoned vs. 27% and 40% of 30 control nests on the two islands, 1999: two treated nests, three control nests sprayed with water and three undisturbed nests were abandoned). There were no significant differences in chick survival between treatment and control nests in either colony in either year.
A randomised, replicated and controlled trial over two breeding seasons in 2001-2 in British Columbia, Canada (Dawson 2004) found that tree swallow Tachycineta bicolor nests treated with insecticide (in 2001: 38.1% diatomaceous earth, 0.2% pyrethrins and 1.0% piperonyl butoxide; 2002: 80% silicon dioxide) contained significantly fewer bird fleas Ceratophyllus idius and blow flies Protocalliphora spp. than untreated nests (approximately 25 fleas and 28 blowflies in 23 treated nests vs. 350 fleas and 50 blowflies in 32 control nests).
A randomised, replicated and controlled trial at two brown pelican Pelecanus occidentalis colonies in South Carolina, USA (Eggert & Jodice 2008) found that treating pelican nests with insecticide (175 ml of a 0.5% dilution of Rabon® 50 WP sprayed on to nests) significantly reduced the number of ticks Carios capensis on pelican chicks compared to control nests at one colony in 2004 but not on the other (Marsh Island: 1.1 ticks/chick for 45 treated chicks vs. 10.4 ticks/chick for 50 untreated chicks; Crab Bank: 0.01 ticks/chick for 48 treated chicks vs. 0.1 ticks/chick for 50 untreated nests). There were no differences in tick burden between treatment and control nests in 2005. There were also no differences between treatment and control nests in terms of survival of chicks to 21 days or chick growth rates.
A replicated, controlled study from June-July in 2007 in 36 experimental and 19 control nestboxes in an agricultural habitat in Alberta, Canada (Stephenson et al. 2009), found that tree swallow Tachycineta bicolor nestlings subject to ectoparasite removal through feather removal and insecticide did not grow faster or fledge earlier than control nestlings. Nestlings in control nests were larger than those in nests from which feathers were removed and insecticide applied (17.5 compared to 16.2 and 16.1 g/unit time respectively). Growth rate was positively related to number of feathers in the nest. Time between hatching and fledging and number of chicks fledged did not differ (20.4, 20.8 and 20.6 days between hatching and fledgling; 5.8, 5.4 and 5.5 nestlings fledged for control, feathers removed and insecticide nests respectively). The abundance and composition of parasitic arthropods in the nest did not differ between treatments. The authors conclude that feathers did not serve as an ectoparasite barrier, though they affected nestlings’ growth rates positively.
A randomised, replicated and controlled study in 2006-7 in a mixed grassland-wetland-forest ecosystem in British Columbia, Canada (Wiebe 2009) found that northern flicker Colaptes auratus nests that were fumigated (with diatomaceous earth and 0.5% pyrethrin) had fewer ectoparasitic flies Carnus hemapterus than control nests (fewer than five parasites/nestling for 33 fumigated nests vs. 10-17 parasites/nestling for 44 control nests). Chicks from control nests also fledged at lower weights than those from fumigated nests (129-132 g for females and 133-136 g for males in fumigated nests vs. 124-126 g for females and approximately 129 g for males in control nests). These relationships held for both new and reused nests.
- Roby D.D., Brink K.L. & Wittmann K. (1992) Effects of Bird Blowfly Parasitism on Eastern Bluebird and Tree Swallow Nestlings. The Wilson Bulletin, 104, 630-643
- Dufva R. & Allander K. (1996) Variable effects of the hen flea Ceratophyllus gallinae on the breeding success of the great tit in relation to weather conditions. Ibis, 138, 772-777
- Alves M.A.S. (1997) Effects of ectoparasites on the sand martin Riparia riparia nestlings. Ibis, 139, 494-496
- Brown C.R & Brown M.B. (1999) Fitness components associated with laying date in the cliff swallow. The Condor, 101, 230-245
- Hurtrez-Boussès S., Renaud F., Blondel J. & Perret P. (2000) Effects of Ectoparasites of Young on Parents' Behaviour in a Mediterranean Population of Blue Tits. Journal of Avian Biology, 31, 266-269
- Bouslama Z., Lambrechts M.M., Ziane N., Djenidi R. & Chabi Y. (2002) The effect of nest ectoparasites on parental provisioning in a north-African population of the blue tit Parus caeruleus. Ibis, 144
- Norcross N.L. & Bolen E.G. (2002) Effectiveness of nest treatments on tick infestations in the eastern brown pelican. Wilson Bulletin, 114, 73-78
- Dawson R.D. (2004) Efficacy of diatomaceous earth at reducing populations of nest-dwelling ectoparasites in tree swallows. Journal of Field Ornithology, 75, 232-238
- Eggert L.M.F. & Jodice P.G.R. (2008) Growth of brown pelican nestlings exposed to sublethal levels of soft tick infestation. The Condor, 110, 134-142
- Stephenson S., Hannon S. & Proctor H. (2009) The function of feathers in tree swallow nests: insulation or ectoparasite barrier? The Condor, 111, 479-487
- Wiebe K.L. (2009) Nest excavation does not reduce harmful effects of ectoparasitism: an experiment with a woodpecker, the northern flicker Colaptes auratus. Journal of Avian Biology, 40, 166-172