A Study into the Raptor Predation of Domestic Pigeons: By Colin Shawyer, Roger Clarke and Nicholas...
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Book review A Study into the Raptor Predation of Domestic Pigeons By Colin Shawyer, Roger Clarke and Nicholas Dixon. (2000). Published (product code 99 WACD 0942) and distributed free by the Department of the Environment, Food and Rural Affairs, Species Branch, Temple Quay House, Bristol BS1 6EB. 154pp. Paperback. The Raptor Working Group was established in 1995 by the Department of the Environment (later DETR but currently the Department for the Environment, Food and Rural Affairs) and part of its remit was to consider the potential impact of birds of prey on the sport of pigeon racing. The absence of quantitative data on racing pigeon losses to raptors led to a DETR com- missioned research project that was awarded to the Hawk and Owl Trust; the volume under review is the resulting report. The report concludes that annual losses of racing pigeons in the UK totalled 52%. In view of this sub- stantial figure, the report goes on to consider potential causes of pigeon loss, and to assess whether Peregrines, Goshawks and/or Sparrowhawks could account for a significant proportion of these losses. The report’s conclusions appear to exonerate raptors as a significant cause of racing pigeon losses at a national level but, unfortunately, many of the main conclusions of the report are based on flawed method- ology. For example, the authors conclude that incapa- city through exhaustion or starvation was the most significant cause of pigeon losses, accounting for 42% of birds that failed to return home, whilst only 7% were considered to have been lost as a result of attacks by raptors. The figures are based on a sample of 417 racing pigeons that were handed in to animal rescue centres, so the sample is biased towards pigeons that were lost under circumstances where they were likely to be recovered by members of the public. Pigeons eaten by birds of prey do not end up in animal rescue centres thus extrapolation from this biased sample, to pigeon losses in general, is fundamentally flawed. Another example of the flaws in the report come from an analysis of the number of racing pigeon rings recov- ered at Peregrine nesting sites. From this, the authors estimated that, during the racing season, predation by Peregrines would rarely exceed two to four pigeons per week. In terms of ‘meat weight’, this is far less than even the daily estimated requirement found in other studies. The assumption that the number of rings found is an accurate reflection of the number of racing pigeons killed is probably incorrect because terrain accessibility greatly influences the chance of finding rings and those in pellets can be regurgitated at sites well away from the nest. Furthermore, the ring recovery data are not extrapolated to account for predation over the whole racing season or the Peregrines’ post-fledging period, when juveniles and adults remain in the nesting area and continue to kill pigeons until September. This methodology significantly under-estimates the number of racing pigeons killed by Peregrines in the UK. Counter-intuitively, the fact that Peregrines kill a large number of racing pigeons does not necessarily mean that they have a direct, detrimental impact on the sport. If a significant proportion of pigeons are already lost prior to being killed and/or mortality is not region- ally localised, the potential impact is reduced. The authors address the first point but not the second. Assessing which pigeons were already lost prior to pre- dation is difficult because some pigeons take several days to return home, after being temporarily lost en route. Thus, contrary to the assumption in this report, not all stray pigeons are permanently lost. The authors adopted a pragmatic model of a direct line of flight to assess which pigeons were off-line (i.e. strays) when killed by Peregrines. This is unlikely to be realistic as pigeon race routes are influenced by wind direction, landscape features and contours. The report states that 42% of pigeons were off-line when killed (though there is little discussion of the regional variation found) and a further 12% were considered to have overshot their lofts. The accuracy of a linear model to assess which pigeons were strays needs to be tested and the propor- tion of ‘off-line’ birds that eventually return home should be determined before any significance can be attached to these findings. The report further states that that 36% of racing pigeons killed were ‘race ferals’ i.e. lost at least one year prior to being killed. This is a remarkable figure considering that another finding of this report concluded that less than 4% of feral pigeons PII: S0006-3207(01)00217-8 Biological Conservation 105 (2002) 405–406 www.elsevier.com/locate/biocon
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Transcript of A Study into the Raptor Predation of Domestic Pigeons: By Colin Shawyer, Roger Clarke and Nicholas...
Book review
A Study into the Raptor Predation of Domestic Pigeons
By Colin Shawyer, Roger Clarke and Nicholas Dixon.(2000). Published (product code 99 WACD 0942) anddistributed free by the Department of the Environment,Food and Rural Affairs, Species Branch, Temple QuayHouse, Bristol BS1 6EB. 154pp. Paperback.
The Raptor Working Group was established in 1995by the Department of the Environment (later DETRbut currently the Department for the Environment,Food and Rural Affairs) and part of its remit was toconsider the potential impact of birds of prey on thesport of pigeon racing. The absence of quantitative dataon racing pigeon losses to raptors led to a DETR com-missioned research project that was awarded to theHawk and Owl Trust; the volume under review isthe resulting report.The report concludes that annual losses of racing
pigeons in the UK totalled 52%. In view of this sub-stantial figure, the report goes on to consider potentialcauses of pigeon loss, and to assess whether Peregrines,Goshawks and/or Sparrowhawks could account for asignificant proportion of these losses.The report’s conclusions appear to exonerate raptors
as a significant cause of racing pigeon losses at anational level but, unfortunately, many of the mainconclusions of the report are based on flawed method-ology. For example, the authors conclude that incapa-city through exhaustion or starvation was the mostsignificant cause of pigeon losses, accounting for 42% ofbirds that failed to return home, whilst only 7% wereconsidered to have been lost as a result of attacks byraptors. The figures are based on a sample of 417 racingpigeons that were handed in to animal rescue centres, sothe sample is biased towards pigeons that were lostunder circumstances where they were likely to berecovered by members of the public. Pigeons eaten bybirds of prey do not end up in animal rescue centresthus extrapolation from this biased sample, to pigeonlosses in general, is fundamentally flawed.Another example of the flaws in the report come from
an analysis of the number of racing pigeon rings recov-ered at Peregrine nesting sites. From this, the authorsestimated that, during the racing season, predation by
Peregrines would rarely exceed two to four pigeons perweek. In terms of ‘meat weight’, this is far less than eventhe daily estimated requirement found in other studies.The assumption that the number of rings found is anaccurate reflection of the number of racing pigeonskilled is probably incorrect because terrain accessibilitygreatly influences the chance of finding rings and thosein pellets can be regurgitated at sites well away from thenest. Furthermore, the ring recovery data are notextrapolated to account for predation over the wholeracing season or the Peregrines’ post-fledging period,when juveniles and adults remain in the nesting areaand continue to kill pigeons until September. Thismethodology significantly under-estimates the numberof racing pigeons killed by Peregrines in the UK.Counter-intuitively, the fact that Peregrines kill a
large number of racing pigeons does not necessarilymean that they have a direct, detrimental impact on thesport. If a significant proportion of pigeons are alreadylost prior to being killed and/or mortality is not region-ally localised, the potential impact is reduced. Theauthors address the first point but not the second.Assessing which pigeons were already lost prior to pre-dation is difficult because some pigeons take severaldays to return home, after being temporarily lost enroute. Thus, contrary to the assumption in this report,not all stray pigeons are permanently lost. The authorsadopted a pragmatic model of a direct line of flight toassess which pigeons were off-line (i.e. strays) whenkilled by Peregrines. This is unlikely to be realistic aspigeon race routes are influenced by wind direction,landscape features and contours. The report states that42% of pigeons were off-line when killed (though thereis little discussion of the regional variation found) and afurther 12% were considered to have overshot theirlofts. The accuracy of a linear model to assess whichpigeons were strays needs to be tested and the propor-tion of ‘off-line’ birds that eventually return homeshould be determined before any significance can beattached to these findings. The report further states thatthat 36% of racing pigeons killed were ‘race ferals’ i.e.lost at least one year prior to being killed. This is aremarkable figure considering that another finding ofthis report concluded that less than 4% of feral pigeons
PII : S0006-3207(01 )00217-8
Biological Conservation 105 (2002) 405–406
www.elsevier.com/locate/biocon
carried racing rings. Even if we assume that one in 25feral pigeons are ringed it seems incredible that such alarge proportion are eaten by Peregrines. For everyringed feral pigeon eaten by Peregrines are there 24unringed ferals killed? If so, where do Peregrines in theuplands of Britain obtain these feral pigeons, or areringed feral pigeons more likely to be killed than theirunringed counterparts? A probable explanation for thisfinding is that old rings from pigeons killed in previousseasons were included in the analysis. The authors couldhave confined their analysis to rings found on fresh legsor within recent pellets. To conclude, the figures pre-sented in this report and subsequently adopted by theRaptor Working Group are based on flawed method-ology and there is little statistical analysis of the data.
There are inconsistencies in the data throughout thereport and we have merely concentrated on the mainfindings in this review. The implication of a diminishingnumber of pigeon fanciers on Peregrine conservation isnot discussed. This trend could possibly have a dramaticimpact on the number of breeding Peregrines within theUK and significantly reduce the importance of the UKPeregrine population in a European context.
Andrew Dixon, Ian R. HartleyBiological Sciences
Lancaster UniversityLancaster LA1 4YQ
UKE-mail address: [email protected]
406 Book review / Biological Conservation 105 (2002) 405–406
