Abstract
We investigated the variations in the diets of barn owls (Tyto alba) along a rural to urban gradient in the Lower Fraser Valley of southwestern British Columbia, Canada. Our objectives were to determine the food preferences of barn owls in different habitat types and to assess both seasonal and annual variations in their diets. In particular, given the increased incidences and concentrations of second generation anticoagulant rodenticide (SGAR) residues in barn owls, we were interested in determining whether there was any relationship between the degree of urbanization surrounding their nest/roost sites and the proportion of commensal rodents (Rattus norvegicus, Rattus rattus, Mus musculus) in their diet. In total, 8,941 individual prey remains were identified. The proportion of rats consumed increased significantly with the amount of urbanization within home ranges. However, voles (primarily field voles, Microtus townsendii) were the main prey item for all sites irrespective of surrounding land use within home ranges. Shrews were the second most consumed prey species (10.8 ± 8 %), and were found predominantly in the diet of barn owls nesting in more rural landscapes. The dominance of field voles in the diet was also reflected in the food-niche breadth, which was consistently low for all sites across the rural to urban gradient. Interestingly, barn owls were found nesting in highly urban environments (66–95 % urbanization), where bait stations containing SGARs were regularly used. This, combined with the increased consumption of rats in more urban environments, illustrates why the SGAR exposure rate in barn owls is substantial and rising.
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References
Albert CA, Wilson LK, Mineau P, Trudeau S, Elliott JE (2010) Anticoagulant rodenticides in three owl species from Western Canada, 1988–2003. Arch Environ Contam Toxicol 58:451–459
Beecham TD (1979) Survival in fluctuating populations of the vole Microtus townsendii. Can J Zool 57:2375–2384
Bing Maps (2010) Search: southwestern B.C. http://www.bing.com/maps/?FORM=HDRSC4. Accessed 3 Dec 2012
Bock CE, Vierling KT, Haire SL, Boone JD, Merkle WW (2002) Patterns of rodent abundance on open-space grasslands in relation to suburban edges. Conserv Biol 16:1653–1658
Brakes CR, Smith CH (2005) Exposure of non-target small mammals to rodenticides: short-term effects, recovery and implications for secondary poisoning. J Appl Ecol 42:118–128
Campbell RW, Manuwal AD, Harestad AS (1987) Food habits of the common barn-owl in British Columbia. Can J Zool 65:578–586
Charter M, Izhaki I, Shapira L, Leshem Y (2007) Diets of urban breeding barn owls (Tyto alba) in Tel Aviv, Israel. Wilson J Ornithol 119:484–485
Christensen TK, Lassen P, Elmeros M (2012) High exposure rates of anticoagulant rodenticides in predatory bird species in intensively managed landscapes in Denmark. Arch Environ Contam Toxicol 63:437–444
Cowan I (1942) Food habits of the barn owl in British Columbia. Murrelet 23:48–53
Cox PR, Smith RH (1990) Rodenticide ecotoxicology: assessing non-target population effects. Funct Ecol 4:315–320
Dawe NK, Runyan CS, McKelvey R (1978) Seasonal food habits of the barn owl (Tyto alba) on the Alaksen national wildlife area, British Columbia. Can Field Nat 92:151–155
Doerkson GP (1969) An analysis of barn owl pellets from Pitt Meadows, British Columbia. Murrelet 50:4–8
Elliott JE, Hindmarch S, Albert CA, Emery J, Mineau P, Maisonneuve F (2014) Exposure pathways of anticoagulant rodenticides to nontarget wildlife. Environ Monit Assess 186:895–906. doi:10.1007/s10661-013-3422-x
Feng AYT, Himsworth CG (2013) The secret life of the city rat: a review of the ecology of urban Norway and black rats (Rattus norvegicus and Rattus rattus). Urban Ecosyst. doi:10.1007/s11252-013-0305-4
Hager SB (2009) Human-related threats to urban raptors. J Raptor Res 43:210–226
Henny CJ, Grove RA, Kaiser JL, Johnson BL, Furl CV, Letcher RJ (2011) Wastewater dilution index partially explains observed polybrominated diphenyl ether flame retardant concentrations in osprey eggs from Columbia River Basin, 2008–2009. Ecotoxicology 20:682–697
Hindmarch S, Krebs EA, Elliott JE, Green DJ (2014) Urban development reduces the fledgling success of barn owls in the Fraser Valley, British Columbia, Canada. Condor (in press)
Lambert O, Pouliquen H, Larhantec M, Thorin C, L’Hostis M (2007) Exposure of raptors and waterbirds to anticoagulant rodenticides (difenacoum, bromadiolone, coumatetralyl, coumafen, brodifacoum): epidemiological survey in Loire Atlantique, France. Bull Environ Contam Toxicol 79:91–94
Li X, Poon CS, Liu PS (2001) Heavy metal contamination of urban soils and street dusts in Hong Kong. Appl Geochem 16:1361–1368
Lima LL, Salmon TP (2010) Assessing some potential environmental impacts from agricultural anticoagulant uses. Proc Vertebr Pest Conf 24:199–203
Love RA, Webbon C, Glue DE, Harris S (2000) Changes in the food of British barn owls (Tyto alba) between 1974 and 1997. Mammal Rev 30:107–129
Marti CD (1974) Feeding ecology of four sympatric owls. Condor 76:45–61
Marti CD (1988) A long-term study of food-niche dynamics in the common barn-owl: comparisons within and between population. Can J Zool 66:1803–1812
Marti CD, Bechard M, Jaksic FM (2007) Food habits. In: Bildstein KL, Bird DM (ed) Raptor research and management techniques. 2nd edn. Raptor Research Foundation, Hancock House Publishers, Blaine, p 129–149
Marti CD, Poole AF, Bevier LR (2005) The birds of North America Online. In: Poole A (ed) Ithaca: Cornell Lab of Ornithology barn owl (Tyto alba) http://bna.birds.cornell.edu.proxy.lib.sfu.ca/bna/species/001. doi:10.2173/bna.1. Accessed 15 Nov 2012
McKinney ML (2002) Urbanization, biodiversity and conservation. Bioscience 52:883–890
McMillin SC, Hosea RC, Finlayson BF, Cypher BL, Mekebri A (2008) Anticoagulant rodenticide exposure in an urban population of the San Joaquin kit fox. Proc Vertebr Pest Conf 23:163–165
Merson MH, Byers RE, Kaukeinen DE (1984) Residues of the rodenticide brodifacoum in voles and raptors after orchard treatment. J Wildl Manag 48:212–216
Metro Vancouver (2008) Metro Vancouver http://www.metrovancouver.org/Pages/default.aspx. Accessed 29 Sept 2008
Morris WI (1973) Rats in the diet of the barn owl (Tyto alba). Notes Mammal Soc 39:540–545
Murray M (2011) Anticoagulant rodenticide exposure and toxicosis in four species of birds of prey presented to a wildlife clinic in Massachusetts, 2006–2010. J Zoo Wildl Med 42:88–97
Nagorsen DW (1996) Opossums and shrews and moles of British Columbia. University of British Columbia Press, Vancouver
Nagorsen DW (2005) Rodents and lagomorphs of British Columbia. University of Washington Press, Seattle
Newsome SD, Park JS, Henry BW, Holden A, Fogel ML, Linthicum J, Chu V, Hooper K (2010) Polybrominated diphenyl ether (PBDE) levels in peregrine falcon (Falco peregrinus) eggs from California correlate with diet and human population density. Environ Sci Technol 4:5248–5255
North MEA, Teversham JM (1983) The vegetation of the flood plains of the Lower Fraser, Serpentine and Nicomekl rivers, 1859 to 1890. Syesis 17:47–66
Raczynski J, Ruprecht AL (1974) The effect of digestion on osteological composition of owl pellets. Acta Ornithol 14:25–38
Riley SPD, Bromley Poppenga CRH, Uzai FA, Whited L, Sauvajot RM (2007) Anticoagulant exposure and notoedric mange in bobcats and mountain lions in urban southern California. J Wildl Manag 71:1874–1884
Salvati L, Ranazzi L, Manganaro A (2002) Habitat preferences, breeding success, and diet of the barn owl (Tyto alba) in Rome: urban versus rural territories. J Raptor Res 36:224–228
Steenhof K, Kochert MN (1988) Dietary responses of three raptor species to changing prey densities in a natural environment. J Anim Ecol 57:37–48
Stone WB, Okoniewski JC, Stedelin JR (1999) Poisoning of wildlife with anticoagulant rodenticides in New York. J Wildl Dis 35:187–193
Storen J (2011) British Columbia in 2036, People 2036. BC Stats. http://www.bcstats.gov.bc.ca/StatisticsBySubject/Demography/PopulationProjections.aspx. Accessed 31 March 2013
Taitt MJ, Gipps JHW, Krebs CJ, Dundjerski Z (1981) The effect of extra food and cover on declining populations of Microtus townsendii. Can J Zool 59:1593–1599
Taylor IR (1994) Barn owls. Predator–prey relationships and conservation. Cambridge Univ, Press, Cambridge
Teta P, Hercolini C, Cueto G (2012) Variation in the diet of western barn owls (Tyto alba) along an urban–rural gradient. Wilson J Ornithol 124:589–596
Thomas PJ, Mineau P, Shore RF, Champoux L, Martin PA, Wilson LK, Fitzgerald G, Elliott JE (2011) Second generation anticoagulant rodenticides in predatory birds: probabilistic characterisation of toxic liver concentrations and implications for predatory bird populations in Canada. Environ Int 37:914–920
Van Metre PC, Mahler BJ, Furlong ET (2000) Urban sprawl leaves its PAH signature. Environ Sci Technol 34:4064–4070
Walker LA, Turk A, Long SM, Wienburg CL, Best J, Shore RF (2008) Second generation anticoagulant rodenticides in tawny owls (Strix aluco) from Great Britain. Sci Total Environ 392:93–98
Walker LA, Chaplow JS, Llewellyn NR, Pereira MG, Potter ED, Sainsbury AW, Shore RF (2012) PBMS report on rodenticides https://wiki.ceh.ac.uk/download/attachments/134414860/PBMS_Rodenticide_2011_FINAL.pdf?version=1&modificationDate=1361181795000. Accessed Sept 15 2013
Webster JA (1973) Seasonal variation in mammal contents of barn owl castings. Bird Study 20:185–196
Acknowledgments
We are most grateful to Lindsay Davidson for her help searching for barn owl pellets and for spending many hours in the lab dissecting owl pellets and identifying prey species. We are most grateful to private and commercial landowners for giving us access and allowing us to monitor barn owls on their properties and collect barn owl pellets. Without their cooperation and kindness this research would not have been possible. We wish to thank the two independent reviewers for their efforts reviewing this manuscript. Their feedback has resulted in a better manuscript. Funding for this research was provided to John Elliott by the Pesticide Science Fund of Environment Canada.
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Hindmarch, S., Elliott, J.E. A specialist in the city: the diet of barn owls along a rural to urban gradient. Urban Ecosyst 18, 477–488 (2015). https://doi.org/10.1007/s11252-014-0411-y
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DOI: https://doi.org/10.1007/s11252-014-0411-y