Revealing the fortunes of birds: what satellite transmitters tell us
Here Ian Thomson, RSPB Scotland's Head of Investigations, explains why fitting satellite transmitters to birds of prey is so important and what the data provided tells us about the these birds.
A golden eagle chick in Galloway who was fitted with a satellite transmitter before fledging in 2015 and disappeared in May 2016 (Dave Anderson, Scottish Raptor Study Group)
Ringing has been an established part of the scientific study of birds for over a hundred years. It has provided a fascinating insight into survival rates, important summer and wintering areas, and even the migration routes of a huge range of species. But, ringing has its limitations, with a bird having to be either found dead or re-trapped in order for the ring to be read.
Various developments in recent decades including the use of colour rings, neck collars and wing tags have allowed birds to be individually identified without having to catch them, but are still dependent on an observer being in the right place at the right time in order to link a bird with a location. Sometimes questions of science have to wait to be answered until technology has advanced enough to allow for that to happen.
Such is the case with the movement of birds: before the miniaturisation of GPS satellite tags, there were huge gaps in our knowledge on the daily movements of birds, important feeding areas and overnight roost sites. Satellite transmitters have changed all that. Now, the movements of a bird can be followed on a computer, allowing a fascinating insight into their daily travels, identification of roosting or nest sites and even allowing you to follow their migration across continents and oceans all with incredible accuracy.
A white-tailed eagle being fitted with a satellite transmitter in 2012 (Dean Bricknell, rspb-images.com)
It must be an amazing experience, fitting a satellite transmitter to a young bird of prey, with a feeling of great anticipation as you know you will be able to maintain a relationship with that bird for the following few years, knowing where it has gone and how it is faring.
I work closely with several people who have undergone the years of training, practice and supervision necessary to get them the unique skill-set that has allowed them to be licensed to fit satellite transmitters to birds like ospreys, red kites and hen harriers. Sadly, working for the RSPB Investigations team, my experience with satellite-tagged birds comes not in the early days of these young birds lives as they move away from their nest sites to explore the world. It happens when those experts, from a variety of agencies and organisations who are monitoring the birds, tell me they think there is a problem; a bird appears to have stopped moving, or seems to have disappeared.
One of our first experiences of this was back in 2009, when the signal given out by the transmitter fitted to a young golden eagle, named “Alma”, showed that the bird appeared to have stopped moving. Accompanied by police officers, we went to the location, and found her body, lying face-down in the heather on a grouse moor in the heart of the Angus glens in eastern Scotland. Her body was submitted to the laboratory of Science and Advice for Scottish Agriculture for post-mortem testing. Within a few days, the results came back – she had been poisoned with the banned pesticide, carbofuran.
Alma (courtesy Ewan Weston)
A follow-up operation, led by the police, searched the area, including estate buildings, to try to identify those responsible. But, as is often the case, there was not sufficient evidence found to enable a prosecution. However, the publicity surrounding this case showed very clearly that as well as giving very good information about where satellite-tagged birds were living, it could also show where they were dying.
In subsequent years, there have been further high profile cases where satellite-tagged birds have been illegally killed: the severed legs and wing tags of a red kite found stuffed in a hole in the moss on an Inverness-shire grouse moor in 2010; a golden eagle found poisoned on a grouse moor in the Strathdon area of Aberdeenshire in 2011; a golden eagle dumped under a tree after being illegally trapped on an Angus grouse moor in 2012; golden eagle “Fearnan” poisoned on another Angus grouse moor in 2013; hen harrier “Annie” found shot on a South Lanarkshire grouse moor in 2015.
Annie (John Wright)
There is a depressing pattern here – protected birds of prey found illegally killed on grouse moors. Of course, this is nothing new. In late 2015 we published a report documenting a total of 779 birds of prey confirmed as having been illegally killed in Scotland between 1994 & 2014. A significant majority of these victims were found on land where management for gamebirds, and particularly intensive driven grouse shooting, dominates the landscape.
One thing that has become apparent, however, is that there has been a decline in the number of detected illegal poisoning incidents in Scotland over the last few years. We don’t for one minute think this is coincidence, and is almost certainly linked to the increasing use of satellite transmitters. Publicity around incidents has very clearly shown that if you put poison baits out in our countryside, there is a chance that a satellite-tagged bird will become a victim, and those monitoring these birds will follow it up. The criminals killing our protected raptors don’t want to be caught, so now, perhaps, the risk of using poison is too high?
But that doesn’t mean that the killing of our birds of prey has declined. Despite claims by some to the contrary, there is no evidence to support this. What we have seen is merely a change in tactics, away from the use of poison. Contrast this with the situation south of the border, where there are no satellite-tagged eagles (indeed there are no eagles south of the border). Here the use of illegal poisons shows no signs of a reduction.
Map showing where eight golden eagles fitted with satellite transmitters were last recorded (RSPB Scotland)
In Scotland, what we are now seeing is satellite-tagged birds simply “disappearing”, as is the case of eight golden eagles in the northern Monadhliath mountains in under five years. This isn’t the first time we have seen this pattern – we have other clusters of locations where birds have simply vanished – upper Donside, for example, is an area where one satellite-tagged golden eagle was found poisoned in 2011, but four further satellite-tagged eagles, including a young white-tailed eagle, disappeared in the same area over the following three years.
Some will claim that these disappearances are the results of transmitter malfunctions, or birds dying naturally. Firstly, the experience of those who have fitted and monitored many of these transmitters, both in the UK and elsewhere, is that they are incredibly reliable pieces of kit, with malfunction exceptionally rare. Secondly, if a bird dies naturally, or if a transmitter becomes detached the transmitter will continue to give out location data, allowing it to be found. Indeed, we have recovered a number of these birds that have died as a result of starvation or tags that have come off the birds.
In short, if satellite-tagged birds die naturally, in the vast majority of cases we find them, because their transmitters keep sending out location data. In contrast, in the case of the “disappearing” birds, this is almost exclusively happening in areas of driven grouse shooting management. We don’t find the bodies of the bird, and we get no more data from the transmitter.
Coincidence? I think not.
As this year’s cohort of young raptors take to Scotland’s skies, fitted with satellite-transmitters, with the full support of some of our more progressive landowners, I’m afraid I can’t feel positive for their future. Of course, I hope they live long enough to breed and raise families themselves. But realistically, I know that a good many of them will “disappear” on grouse moors, never to be seen or heard from again.
Self-regulation by Scotland’s gamebird shooting industry has patently failed. If you want to give these young harriers, eagles and other birds of prey an improved chance of living long enough to set up their own nesting territory and fledge their own youngsters, you’ll join with RSPB Scotland in supporting this Scottish parliamentary petition, launched recently by the Scottish Raptor Study Group, and calling for licensing of gamebird shoots in Scotland.
Charlie McMurray is an intern at RSPB Scotland working on 'all nature' projects: mammals, amphibians and insects. This is her latest update on natterjack toads.
By the beginning of May, the noisy natterjack toads at Mersehead were out in full force for the first time this year. Their loud chorus was the cue we needed to begin the final round of our three-year surveys to estimate the population size. Three surveys were performed at night each year, in which every toad we found was captured, photographed and identified by the wart pattern on its back.
Each of these patterns is as unique as a snowflake, so we can recognise individuals without marking them. The proportion of recaptured toads to those caught only once is suggestive of how big the population is. For example, if the majority of individuals weren’t found again, the population is probably relatively large, and vice versa.
To find the recaptures from the photos, we’ve been testing an identification programme called Interactive Individual Identification Software (I3S), as in ‘Nattering with Natterjacks’. The results from the previous two years’ photos were disappointing because the toads were flaunting such a wide range of poses, skewing their wart patterns. I3S, therefore, couldn’t compare the patterns easily.
In the past, the toads were photographed against a laminated sheet, but this year we worked on limiting their movements. All sorts of cunning devices were considered, from restraining them inside petri dishes to creating plunger cages, where the toad would be pushed upwards and gently held against netting. But, with their breeding season looming ever closer, we remained unconvinced.
Our most exemplary toad, Dave, demonstrating the toad-sponge technique. Dave has given himself up twice every year, so we know he’s been roaming the merse for at least six.
Just as the toads started to emerge from their winter hideouts, an idea sprang to mind: the toads could simply sit inside hollows cut out of basic sponges. The toads seemed to approve, sitting calmly, possibly somewhat perplexed. As burrowers, perhaps they felt safer within a hollow or maybe the rougher material wasn’t as foreign to them as the slippery sheet.
After the fun bit, it was back indoors to plug the photos into I3S. First, some good news: when the software found the correct match, it was always ranked first out of fifty possibilities. Previously, the match could’ve been anywhere in that long list, so the upgrade was much more time-efficient. The not-quite-so-good news is that the software found eleven out of fourteen matches, which means there’s still some fine-tuning to do. It’s a big improvement on the results from the last two years though.
Now, the population size estimates – the moment we’ve all been waiting for! In 2014, the year of the storm that prompted these surveys, there were estimated to be 30 breeding males. In the second year, the number rose steeply to 156. The figure increased once again to a staggering 248 males this year. We’ve focussed on the males because their breeding behaviour is much more repetitive than the females’, who only come to the breeding pools once, maybe twice, a season. That means we’re highly unlikely to recapture them.
This juvenile male, only 2.2cm long, worked his way into a survey. He was surrounded by calling adult males in a breeding pool, so he’s a little too big for his boots.
Reflecting on the population predictions, we’ve speculated that there were so few breeding individuals in 2014 because the conditions were too bad for spawn to survive. It’d have been a huge loss of energy for the adults with a great deal of risk. We’re cautious about 2016’s figure, believing that it overshot the mark. The weather for the second survey of the year wasn’t ideal, so not many toads were captured, meaning that there was less chance of finding recaptures. Remember, the fewer the recaptures, the bigger the population is suggested to be.
If we take 2015 to be the most reliable estimate for a normal year, the entire adult population (including females) could be anywhere between 265 and 374 individuals. Considering we only predicted it to consist of about 30 before the surveys started, this is extremely positive news. It’s also demonstrated how hardy these charismatic little amphibians can be.
The chorus has quietened down now, so here ends our intensive natterjack surveys. The work isn’t over yet, though. It’s still a constant effort to keep the toads’ habitat to their liking. A few were found in new places on the reserve this year, so the question is, is their population expanding or are they beginning to move away? There’s plenty to keep us occupied, so you haven’t heard the last of the natterjack toads.
The Lodge Forest Visitor Centre in Aberfoyle is a five-star visitor attraction run by Forest Enterprise Scotland. It has a wildlife room - which is a joint project between Forest Enterprise Scotland and RSPB Scotland - where visitors can watch fantastic wildlife nearly every day, with webcams showing live nests and highlight reels. It’s been a brilliantly busy summer this year - wildlife officer Jenni Fulton brings us this summary.
During 2016, a pair of ospreys provided no end of drama in Aberfoyle. The male and female were both completely new to the site, having not settled here before. Neither of the birds had been ringed so unfortunately we didn’t know anything about their history, for example their age or where they came from. The pair quickly learned to build and defend a nest, bond with each other and produce three blotchy brown eggs.
When the first was laid, the male was curious about this new object in his nest, but the female was initially reluctant to let him observe or sit on the eggs, until he literally shouldered her aside. He spent ten minutes repeatedly sitting down and standing up, before seemingly getting bored and flying off! Luckily mum was on hand to take over again.
Despite weeks of snow, heavy rain, gales and unseasonably cold temperatures, the birds’ patient egg incubation paid off and they were rewarded with three healthy young chicks - two males and one female. At six weeks old, all three chicks were ringed and both males also had satellite trackers fitted so they can be monitored as they make their first migration to North or West Africa, where they will spend the next few years of their lives.
The osprey chicks fledged in August at around eight weeks of age, although the first flights were heart-stopping as first one, then another failed to make safe landings - clinging on to the edge of the nest before struggling to get back on board. Ospreys can perish if they miss the nest as they may not be able to take off again from a busy forest floor, and they are still dependant on fish being brought in to them by their parents.
Sadly, many ospreys don’t make it to adulthood and often we don’t understand why. But with trackers fitted, the data gathered will allow us to see exactly where these young birds go and whether they survive, which will contribute to the valuable knowledge needed to offer protection for this amazing species in future.
This year at Aberfoyle, we were also privileged to be able to watch a pair of peregrine falcons nesting on a nearby cliff edge. They found a south facing ledge with a slight overhang above, where they were warmed by the morning sun and protected from rain or snow. Four nut-brown eggs hatched after five weeks, producing four perfectly white chicks, which quickly became four boisterous young male birds.
Day after day they grew, until they were no longer fluffy bundles - but slightly smaller versions of their parents, with handsome barring on their chests and distinct black eye masks. With the ledge available to clamber about on, the chicks gradually wandered out of sight more and more often, although at meal times they were quick to reappear for a frantic feeding frenzy. Now in August, they can still be seen and heard flying around nearby.
Unfortunately owls have had a pretty tough season at Aberfoyle, with many of the nest boxes that have been installed to give these animals a home going unused. However, this has been to the benefit of other species such as gooseanders, which have been taking advantage of the spare space and moving in – some managing to lay 12 or more eggs at a time!
As the forest is home to pine martens, the owl boxes need to be positioned so these predators can’t climb down from adjacent trees and get inside. The tree trunks also have to be covered with material they cannot scale. One box we had a camera on was inhabited by barn owls and we knew at least two eggs had been laid. We eventually saw two white fluffy bundles, but then eventually only one chick reaching fledging age.
From the hide, viewing areas and on the wildlife cameras at the site, visitors can also see red squirrels, great spotted woodpeckers, jays, and nuthatches, as well as great, blue and coal tits. Recently a sparrowhawk has taken to catching unwary prey down by the feeders too.
The ospreys may have fledged and left the site now, but you can still view live wildlife footage of plenty of other species, and special films of this year’s families, at the Lodge Forest Visitor Centre. There’s also a special bat event taking place on Saturday 27 August 27. For more information, click here.