Executive Summary
1. A study was undertaken by a partnership between the Scottish Government ( SG), Scottish Natural Heritage ( SNH), and the Scottish Homing Union ( SHU) in response to a request made by the SHU that a legal form of control of Sparrowhawks operating in the vicinity of lofts should be trialled. The trial was devised to test two potential management options: (a) capture, transfer and release (translocation) of Sparrowhawks operating in the vicinity of lofts; and (b) use of visual deterrents at lofts. At the end of the trial, the BTO was contracted by SNH to provide this impartial and independent report on the work carried out.
2. At the outset, 45 lofts that had previously reported a "high level" of Sparrowhawk attacks volunteered to take part in the trial. The aim was to allocate 15 lofts randomly to each of the three treatments: (a) mylar tape as a visual deterrent; (b) Larsen traps for the trapping, transfer and release of Sparrowhawks away from lofts; and (c) controls, where no deterrents were used and no trapping was carried out. In practice, lofts were restricted to particular geographical regions to allow the single contractor to travel between them, and some lofts were swapped between treatment groups ( e.g. when loft owners were unable to commit long periods to oversee operation of a trap).
3. The trial ran from 8 January to 30 April 2009. Useable log books of observations were returned from 23 of the original 45 lofts: 10 from lofts using visual deterrents; 6 from control lofts; and 7 from lofts using Larsen traps (although only two from lofts from which Sparrowhawks were actually caught and translocated).
4. The insufficient sample of lofts that submitted observations for this trial, issues over the experimental design (which were compounded further by the small sample) and the quantity and quality of the observational data collected meant that it was impossible to draw any firm conclusions regarding the effects of the two management types on Sparrowhawk attack rates at pigeon lofts. Furthermore, for a rigorous scientific trial, observers would need to be provided with enhanced training and written guidance on recording observations (including observation durations), and independent validation of a sample of observations would be good practice.
5. Comparisons between lofts revealed high variability in the total numbers of observed attacks by Sparrowhawks, the rates of attack per hour that pigeons were released for exercise, and outcomes of the attacks. It is important to note that the rates provided in this report were derived from a sample of lofts that joined the trial because they had previously reported a "high level" of Sparrowhawk attacks: the rates should not be seen as representative of those at lofts across Scotland more generally.
6. Due to the small sample of lofts from which observations were returned, there was low statistical power, and none of the comparisons between treatments showed a statistically significant result. The available data were not adequate to test whether the use of mylar tape or Sparrowhawk translocation altered attack rates.
7. The short life of the transmitter batteries meant that Sparrowhawks could only be followed for a maximum of nine days after translocation. This limited duration of tracking, and the small number of individuals followed, made it impossible to draw general conclusions about the impacts of translocation on Sparrowhawks ( e.g. of whether the subsequent welfare (body condition) or survival of these individuals matched that of non-translocated Sparrowhawks) or the extent to which Sparrowhawks may eventually return to their capture location.
8. From the 15 lofts at which trapping was attempted, seven Sparrowhawks (all females) were caught at five lofts and released at distances 58-104km from the loft of origin. In the majority of cases, birds were inspected by the SSPCA on capture and/or release and no issues relating to their welfare were raised during the translocation process. Subsequent radiotracking showed that all seven translocated birds survived in the short-term (during up to 9 days of radiotracking) and one that was trapped twice survived for at least 33 days. The one Sparrowhawk that returned to its loft of origin had a similar weight on return as at first capture but no other information was available on the physical condition of the other translocated birds following release.
9. Only one of the seven Sparrowhawks (an adult female) was known to return to the loft of origin: the same bird was recaught and returned once more to a park in the same town as the loft of origin, having travelled over 80km twice. The first return took somewhere between 10 and 32 days, whilst the second return took a maximum of five days.
10. At two lofts from which Sparrowhawks were translocated, an adult female was caught initially, followed by the subsequent capture of an immature female, showing that additional Sparrowhawks can move in quite rapidly to replace translocated birds at least in some places.