Raptor Persecution UK

What you need to know about the satellite tags fitted to the brood meddled hen harriers


Just when you thought the hen harrier brood meddling trial couldn’t be discredited any further…..it turns out that three of the five brood meddled chicks have been fitted with a new, untested type of satellite tag which showed reliability problems right from the start of the trial.

A further five hen harrier chicks, unrelated to the brood meddling trial, were also fitted with these new tags this year (by Natural England), including hen harrier Rosie who was reported ‘missing’ on 17th September (see here) but whose tag started transmitting again three days later (see here).

As far as we are aware, these new tags have not previously been deployed on any harrier species in the UK.

What the actual f….?

It’s anybody’s guess why the project team chose to deploy a new type of tag for the brood meddling trial. The type of tag selected for any animal movement research project will depend on a whole host of things, not least the type of research questions to be addressed by a project (e.g. do you need long-term coarse scale data or do you need shorter-term high resolution data?) but also technical issues such as your study species’ size, weight and ecology as well as tag size, weight and functionality, and there is always the issue of affordability and most definitely reliability.

[A selection of satellite tags on display at the police/researcher satellite tag workshop held earlier this year – photo by Ruth Tingay]

There are a number of tag manufacturers competing in a tight market and competition is high – researchers talk to one another about the tags they’ve been using, the pros and cons of each tag type and which manufacturer’s tags are out performing the others. Tag technology is constantly developing and improving and sometimes researchers will decide to take a risk to test out cutting edge tag technology and novel attachment methods – this is how research advances and methods improve and it’s generally a good thing as long as feedback is widely available to the scientific and technology community from which to learn.

However, if you’re running a politically sensitive research trial where understanding the fate of your study species is crucial (i.e. Natural England’s hen harrier brood meddling trial), and you need to compare survival rates with those of hen harriers tagged in previous years, it is utterly incomprehensible, both politically and scientifically, to elect to try out a new type of tag for that trial because then you have no basis for confidence in the tag’s reliability. It’s completely bonkers!

The hen harrier brood meddling project team agreed to test new tags in the brood meddling trial, apparently for a higher resolution of tracking data. The potential for the tags to fail to provide relevant data was identified as a risk in the Brood Meddling Project Plan and yet still the project team agreed to press on:

We know from an FoI response that at a project team meeting on 27 August 2019, it was noted that there had been unreliability issues with the tags when the chicks were still in the release aviary (the team thought the aviary’s wire mesh may have caused an issue) but there was still an issue with at least one of the harrier’s tags post-release from the aviary:

We also know that in early September news of the tags’ unreliability had reached the gamekeeping community, as evidenced by this gamekeeper’s post on social media. This is a huge worry. Who told the gamekeepers the tags weren’t functioning properly? Talk about giving them a green light to attack! ‘It’s ok lads, you can shoot the harriers this week ‘cos the tags aren’t working properly so they’ll never know it was you’.

We contacted Natural England to ask whether there was any truth in the claims of tag unreliability and to their credit they responded openly, confirming that two of the tags had been malfunctioning but were now back online, that NE hadn’t been concerned about the harriers because they still had ‘eyes on’ the birds in the field so they knew they were ok, and that NE would be talking to the tag manufacturer to understand the issues.

The issue of tag reliability (or in this case, unreliability), cannot be over-estimated. It’s huge. When these three brood meddled hen harriers, along with HH Rosie, went off the radar in September it was completely reasonable for the public and the police to assume they’d been illegally killed because their disappearances fitted the suspicious circumstances of so many before them (at least 72% of all NE-tagged hen harriers have either been illegally killed or presumed to have been killed on grouse moors, according to authoritative research).

We now know Rosie hadn’t been killed – just that her tag had temporarily stopped, for unknown reasons and for an unknown period of time. Perhaps the tag data have already provided a clue to the cause of this (e.g. low battery voltage) but the project team hasn’t commented so we don’t know.

But what of the still missing three brood meddled hen harriers? Can we be sure they’ve been killed? No, we can’t. It’s highly plausible, of course, but it’s equally plausible, knowing what we now know about these particular tags’ unreliability, that the harriers are actually fine but their tags have just stopped functioning for unknown reasons. Will this uncertainty affect Natural England’s decision to issue another brood meddling licence in January?

This situation is obviously unsatisfactory on many levels, not least for the scientific integrity of the brood meddling trial – it’ll be interesting to hear what the scientific advisory group has to say about all this.

Why didn’t they stick with the tags previously used to monitor hen harrier survival? Sure, like any tag those tags also have constraints but their known reliability is excellent (94%) and of course using the same tag type ensures consistency when trying to compare across studies.

And if you think you’ve heard everything there is to hear about the shambolic brood meddling trial, you’re sadly mistaken…..