Continuing advances in wildlife forensics can sometimes help establish the circumstances of a bird’s death or injury. However, some cases will probably always remain a mystery.

We recently received the result of wildlife DNA forensic work undertaken by Science and Advice for Scottish Agriculture (SASA) in relation to two hen harrier deaths. The most recent case related to a failed breeding attempt in Forest of Bowland, Lancashire in June this year. The nest had held a healthy seven chicks but after no sightings of the female, a visit by RSPB staff revealed an empty nest. A search of the surrounding area found a number of hen harrier feathers and we suspected it was a natural predation event, probably by a fox. However, even within the relative safety of United Utilities land hen harriers are not always safe. In 2015, four breeding males ‘went missing’ leading to several nest failures – it seems very likely that most, or all, of these birds were taken out away from the nest sites. Consequently, we decided to see if we could confirm our suspicions about the nest failure this summer. The forensic work at SASA, which was delayed because of Covid-19, did indeed confirm the presence of fox DNA on the recovered feathers – so natural predation it was.

The other case in North Wales was much more intriguing. In 2019, hen harrier Bronwyn fledged from a nest in North Wales having been fitted with a satellite transmitter.

 Bronwyn as a healthy chick prior to fledging in 2019

These devices have demonstrated the intense persecution pressures this species continues to face. A study of 58 hen harriers fitted with satellite tags by Natural England was published last year. This showed the likelihood of hen harriers dying, or disappearing, was ten times higher within areas predominantly covered by grouse moor, compared to areas with no grouse moor. The study revealed that 72% of tagged harriers were either confirmed or considered very likely to have been illegally killed.

There is no doubt that hen harriers continue to be killed and those involved are preventing the tags transmitting incriminating data. Satellite tagging of golden eagles has shown the same problems with sustained persecution, and a case recently reported in September where a satellite tag was wrapped in lead and thrown into a Scottish river shows the lengths people will take to hide evidence of their crimes. We have received intelligence of hen harrier satellite tags being treated in a similar manner and a box lined with roofing lead found during the search of a Scottish grouse estate certainly raised a few eyebrows.

In September 2019 Bronwyn settled into the area around Ruabon Mountain, near Wrexham in North Wales. This raised some concerns as two hen harriers (Aalin and Heulwen) have previously gone missing in suspicious circumstances in this area, much of which is managed for driven grouse shooting.

A raven was also found illegally poisoned on a grouse moor near Ruabon Mountain in 2018, further highlighting our concerns about ongoing persecution in this area. And in May 2019, we received third-hand information that a gamekeeper had shot a satellite tagged hen harrier in this area, though if true, it was not known which bird this may have related to.

Against this sombre background we were keeping a very close eye on the data from Bronwyn’s tag, when things took a turn for the worse. On reviewing the satellite tag data, this showed that at 6.05pm on 24 September Bronwyn was alive near Ruabon Mountain. She had spent around two weeks in this vicinity and had roosted at a number of locations in this area. However, at 9.05 pm, when Bronwyn should have been roosting on the ground, the data showed the satellite tag had no access to any satellites and as a result no GPS location was recorded.

The top left point shows the final position of Bronwyn’s satellite tag

This satellite tag had been reliably providing data since deployment in July. Of the 434 data points provided, on no previous occasion had the tag been unable to access any satellites at all. It had access to three or more on every occasion, with 97.5% of the fixes accessing five or more satellites. So what was going on? At 06.05am the following morning the tag transmitted from an upland location near Maesmaelor nearly 5km to the north west from where Bronwyn had been the previous evening. The data indicated the tag was stationary, suggesting Bronwyn was likely to be dead.

On 27 September a search of the area took place by North Wales Police and RSPB. The satellite tag was recovered from the last known location, however it was no longer attached to Bronwyn. A few hen harrier feathers were found nearby, but no body.


 RSPB Investigations recovering feathers and Bronwyn’s satellite tag

Whilst it was expected that the bird would have roosted in the Ruabon Mountain area on the evening of 24 September, it is possible it could have moved location and subsequently been predated – but why could the tag not communicate with any satellites until the following morning?

One disturbingly scenario to be considered was that the bird had been illegally killed, the tag kept in a situation where it was ‘blind’, and then moved and left at another location before the morning transmission. You may remember the sinister ‘disappearance’ of Fred the golden eagle – had something similar happened here?

The forensic DNA tests by SASA failed to find any fox DNA on Bronwyn’s tag, though the poor weather at the time of recovery and Covid related delays may have played a part in this negative result. So was it some unexplained natural predation event or, more worryingly, another criminal killing of this beleaguered species? Ultimately, whilst highly suspicious, I suspect we may never know for certain. However, it is clear we need to keep a very close watch any hen harriers hanging around this area in North Wales.

In additional to the original turn out from North Wales Police, the RSPB would also like to thank SASA for their forensic work in both these cases, and South Yorkshire Police for their assistance in getting forensic tests undertaken on Bronwyn’s satellite tag.