3 Methodology
The trial ran from 8 January until 30 April 2009. Although observations of Sparrowhawk activity were made at a small number of lofts from as early as 1 November, only results from the trial period are presented here. Licences to operate the Larsen traps were granted by the Scottish Government on 8 January but trapping only began once the contractor was satisfied that all necessary arrangements were in place (15 January). Previously, it was proposed by the Scottish Government that trapping would finish on 31 March, which was deemed to be outwith the Sparrowhawk breeding period. Organisations such as the Scottish Raptor Study Groups ( SRSG) and the Royal Society for the Protection of Birds ( RSPB) were invited to contact SG and SNH if they had concerns that the Sparrowhawk breeding season appeared to have commenced earlier than this date. Observations made by the contract falconer, SNH and RSPB staff indicated that both wild and captive Sparrowhawks were showing signs of breeding behaviour (eg. courtship behaviour and collection of nest material), which gave rise to trapping ending slightly earlier than planned on 27 March. Previous studies have indicated that nest building in most territories begins in March, with some Sparrowhawks starting as early as late February and some as late as April (Newton 1986; I Newton pers comm).
3.1 Visual deterrents
Loft owners were provided with six lengths of one meter strips of flash Mylar tape. Basic instructions on use were provided by SHU (see appended letter that was sent to all participants in the trial: Appendix 2 dated 23/12/08). Any existing deterrents had to be removed before the start of the trial. Suggested sites of attachment included the actual loft or on garden fences but was left to the discretion of the loft owner based on where they judged the deterrent to be most visible to Sparrowhawks. Tape was attached at one end only to allow free movement with the wind. On occasions when Mylar tape was lost or damaged, replacement was provided by post. All lofts operating with Mylar tape received at least one unannounced visit by the contract falconer to ensure that the deterrents were being used appropriately (see Appendix 3).
3.2 Translocation
3.2.1 Trapping techniques
Loft owners were provided by the contractor with a portable standard double catch top entry Larsen trap (1 m 3), blackout material and a transport box. Originally, the SHU had proposed to bait traps with live birds provided with a means of escape in the event of an approaching Sparrowhawk. Prior to the start of the trial, however, several animal welfare groups raised concerns over using live birds. After due consideration, the following forms of bait were used in the traps: (1) racing pigeons previously killed by Sparrowhawks in the vicinity of the loft (within 20 meters), some of which occurred during observations made by loft owners (see section 3.3.1); (2) dead feral pigeons which were provided by the contract falconer, from registered pest control companies, in instances where dead racing pigeons were unavailable (this only occurred at 5 lofts at the start of the trial); and (3) remote control wood pigeon decoys in combination with dead feral pigeons (three lofts in total but only one loft used the decoy consistently throughout the trial). Loft owners using dead racing pigeons placed the traps at the locations where kills of pigeons had previously been made by Sparrowhawks, and carcasses were placed in the traps in the state they were found (including any feathers that had been plucked). As the use of live prey was suggested initially, traps had been modified by the addition of a remotely operated release mechanism to allow pigeons to escape in the event of a Sparrowhawk being caught. This modification was subsequently disabled by the contractor prior to the traps being used in the trial.
Clear guidance on the operation of the traps was also given by the contractor individually and verbally to each loft owner. Traps could only be used during daylight hours, and whilst in operation, had to be checked hourly but preferably every fifteen minutes. Traps when out of use had to be disarmed or covered at all times. All lofts with Larsen traps received at least one unannounced visit by the contract falconer to ensure that the traps were being used appropriately ( Appendix 3). Loft owners were also provided with the phone numbers of the contractor and local volunteers from the Scottish Hawking Club, to be used in the event of a Sparrowhawk being caught. As part of the protocol, the opening and closing times of the traps, as well as the number of bait items, were also to be recorded by loft owners as part of their daily observations made at the loft.
3.2.2 Post capture
Once a Sparrowhawk was caught, the protocol dictated that traps were covered with blackout material and the contractor was notified immediately. The contractor then contacted volunteers from the Scottish Hawking Club who were based locally, in case he was unable to respond within 2 hours (only on two occasions did the contractor not manage to respond within two hours however). Twenty four hour support was also available from local veterinary surgeries in the event of possible feather damage or any other injury to Sparrowhawks. The SSPCA was informed each time a Sparrowhawk was captured and on most occasions a member of SSPCA staff was in attendance either at the loft of capture or the subsequent release site. No issues relating to the welfare of the birds were raised during the trial period.
Following removal from the traps, Sparrowhawks were checked carefully for signs of damage or stress which, if prolonged, could result in paralysis, fitting or heart failure (eg. rapid and audible breathing, wide open bill with the tongue projected forward). In all instances birds were found to be sitting quietly in the traps. Falconry hoods were placed on the birds in order to keep them calm during handling. Sparrowhawks were weighed (see Table 1) and qualitative measurements of muscle tone (such as pectoral muscle under the wing and muscle at the top of the legs), fat (covering the keel bone) and level of dehydration (based on observations of the feet and cere) were recorded. The sex of the bird was also noted: only females were caught during the trial. No measurements of body size were taken, in order to minimise handling time of the bird. Following transfer to the release site (see below), Sparrowhawks were released at least one hour before dark on the day of capture. If this was not possible, birds were held overnight in the transport box until they could be processed and released the following morning.
3.2.3 Release
Prior to release (less than one hour), each Sparrowhawk was inspected again for feather damage or any other signs of stress. In all instances birds were deemed fit for release and for radiotracking. Radio transmitters were then attached by use of an aluminium tube crimped to a central tail feather. The weight of the transmitters was approximately 1% of the mean weight of birds radiotracked during this study (range 314-341 g, mean = 327 g). Further details of the tag, pre-trial testing and the receiving equipment used are given in Appendix 4. A licence to ring Sparrowhawks was not granted until the end of February and therefore the first 4 birds caught as part of the trial were not ringed (apart from bird 3, which was recaught later). Rings issued were registered with the Independent Bird Register 1, a scheme used by falconers to ring captive birds of prey. All rings have a number that uniquely identifies the bird and a telephone number that could be used to notify the IBR in the event of a bird being found by a member of the public. Rings were of the split ring design and were closed using specially adapted pliers.
Release sites were chosen on the basis of having a mixture of habitats, including mature woodland, mixed open woodland, arable and improved pasture, along with access to a water supply and being within sight of an urban area. The minimum distance between the loft and the release site was 30 km. This figure was based on previous work carried out on Goshawks, which showed that few birds returned to the site of capture when moved distances of 30 km or more (Marcstr_m and Kenward 1981). Only two release sites were actually used but more were chosen initially in case translocated Sparrowhawks showed a tendency to stay within the vicinity of the release sites.
3.2.4 Radiotracking
Following release, each bird was immediately monitored using radio telemetry for a period of at least 30 minutes. A follow up visit was then carried out within 24-36 hours and thereafter searches for the bird were made daily until the battery life of the transmitter was exceeded (approximately 9 days) or the bird had not been relocated over a period of 2-3 days.
Searches for birds were made from vantage points across the landscape. Locations were derived using triangulation or by use of a Highly Directional Receiver with three stage attenuation (close, mid, far, which allowed detection up to 100 m, 500 m and 20,000 m respectively). Grid references of resighting locations are based on the position of the observer, with an estimate of distance (and wherever possible direction) to the bird. In most instances these were thought to be within 100 m of the falconer unless specified (worst case scenario accuracy was 2 km). All grid references were imported into Arc GISTM and mapped by the BTO.
3.3 Observations at lofts
3.3.1 Loft owners
Log books with instructions (See Appendix 2) were provided by the SHU to all loft owners in the three groups participating in the trial. All loft owners were asked to provide personal details: their name; loft number; and grid reference or latitude and longitude of the loft. They were also asked to note whether their loft had an aviary attached, as it has been suggested by some SHU members that housing birds in view could increase the likelihood of Sparrowhawk attacks. At the start of the trial, loft owners were asked to document details of pigeons within their lofts including ring numbers, plumage colour and sex (See Appendix 2). This excluded birds known as 'prisoners,' which were never released during the exercise periods.
Loft owners were also required to provide daily information on the following: times of the opening and closing of lofts; the number of pigeons released from the loft and the number that returned; times of Sparrowhawk attacks; consequences of Sparrowhawk attacks; and the ring numbers of pigeons that had failed to return ( Appendix 2). The amount of time spent by loft owners observing Sparrowhawks during the opening times of the lofts was not formally recorded in the vast majority of cases. When lofts were open for short periods, however, as used in the roundabout system (eg. an hour), it was likely that loft owners would have been present the whole time but those using the natural system were less likely to have recorded data over the whole period the loft was open. Additional space for further comments on attacks during each exercise period was also provided ( Appendix 2). If the pigeons were not allowed out to exercise on a particular day, loft owners were also asked to provide a reason. Daily weather conditions were also to be reported. The agreed protocol was for attacks made on the aviary also to be noted, along with any effects observed on the pigeons (See Appendix 2). Any injuries that were incurred as a result of an attack made by a Sparrowhawk were to be photographed, wherever possible. In the event of a fatal attack made by a Sparrowhawk, pigeon corpses were to be retained for inspection to allow verification of the cause of death. In all fourteen instances where the corpses were retained, the contract falconer confirmed that all pigeons had been taken by a raptor (corpses are still held by the contract falconer). The rest of the pigeon kills were likely to have been used as bait in the Larsen traps, although the exact number used for this purpose is unknown.
Information from the log books was originally entered into MS Excel TM spreadsheets by staff at the Scottish Homing Union. All diaries were then provided to the BTO to allow independent checks of assumptions made during inputting. Extensive reformatting was found to be required in order for the required data summaries to be constructed. Pigeons were found to be released for three purposes: (1) exercise (where pigeons flew from and around the loft only); (2) training (where pigeons were taken to another location locally and released to return back to the loft); and (3) racing (when pigeons took part in competitive events over long distances). On most days pigeons were just released for the purpose of exercise. Days on which pigeons were trained (n = 39) or raced (n = 7) were excluded from the summaries since they were not comparable to days when birds were exercised only.
There were several types of events that were recorded as attacks, which were excluded from further summaries of data: (1) 2 attempted Sparrowhawk attacks that were observed whilst the lofts were closed; (2) 3 incidents in which birds were scared back into the loft after sighting a Sparrowhawk which made no attempt to attack the pigeons; (3) 9 events involving attacks made at neighbouring lofts within compound lofts which were reported by a single loft owner; (4) 369 records (105 of which were from a single observer) of 'sightings' of Sparrowhawks recorded that did not represent actual attacks on the loft ( e.g. 'saw Sparrowhawk in field eating feral pigeon); and (5) 11 attacks that were made by Peregrine Falcons (distributed across 6 lofts and with no particular bias concerning treatment group).
Times of attacks were not always recorded by loft owners and it was also noted that if there were multiple attacks within a day, the outcomes were not always attributed to any individual attack. Numbers of Sparrowhawk attacks were summed by day but there were 7 instances where the loft owners did not record absolute numbers (eg. they used the word 'many') and these could therefore not be quantified in the summaries.
Photographs of injured and/or dead birds were provided by only four loft owners, one of whom did not return any log books Although information on the sex of Sparrowhawks involved in attacks at lofts was not collected formally by loft owners, there were no reports of male Sparrowhawks carrying out attacks at lofts during the trial period.
3.3.2 Independent observations
Prior to unannounced visits to the loft owners using traps (see section 3.2.1), informal observations by the contractor were made for a minimum period of half an hour (maximum 2 hours) (see Appendix 3). Sparrowhawks were observed in the vicinity of the loft at only three Larsen trap lofts and no actual attacks were recorded by the contractor (observations are also given in Appendix 3). No observations of Sparrowhawk activity were made at the control or visual deterrent lofts by the contractor.