Spring Explorations

After a prolonged spell of cold and wintry weather, spring is finally in the air. The first Sand Martins have appeared in southern England, and, like at this time last year, the White-tailed Eagles that we released on the Isle of Wight in July 2020 in partnership with Forestry England, are beginning to range widely. We are also building up detailed information on how the 2019 birds are learning to live successfully in the English landscape, as Tim Mackrill explains.

2019 birds

G393

Previous research on the dispersal of young White-tailed Eagles has shown that they often explore extensively during their first two years, before eventually returning to their natal site. This has been exemplified very well in recent months by the behaviour of G393. This immature male, one of the first birds to be released, headed north from the Isle of Wight in mid-September 2019 and subsequently spent the winter in Oxfordshire and Buckinghamshire. It then ranged extensively during spring 2020 – from Suffolk in the east to Gloucestershire in the west – before spending several months in the North York Moors, favouring areas with good numbers of Rabbits. Later in the summer G393 moved south again, lingering for a short while in rural Leicestershire before heading east to West Norfolk on 1^st August. The young male remained in West Norfolk for the next five months, catching Black-headed Gulls at a small reservoir  on the Westacre estate and then spending much of November and December around the Wash. During this period the satellite tracking data showed that the bird flew out onto the mudflats, in search of carrion, on 59% of days from 1^st November. It also frequently visited the mouth of the Great Ouse in the south of the Wash.  

G393 finally left West Norfolk on 4^th January and then, over the course of the next month, slowly made its way back to the Isle of Wight, spending time in rural Lincolnshire and Leicestershire and then arriving at Pitsford Reservoir in Northamptonshire on the evening of 29^th January. It remained in the local area for the next two days, and was seen by a number of local birders exploring bays on the north side of reservoir’s causeway.   

G393 was still present at Pitsford during the morning of 1^st February and was then watched heading south from the dam at 14:00. Remarkably G318, another of the 2019 cohort, which had been residing in the Lincolnshire Wolds for much of the winter was now also flying south and arrived in a wood just over two miles to the west, as G393 was circling south of the Pitsford dam. It seems very likely that good weather and the sight of another White-tailed Eagle had enticed the female south, because she subsequently retuned to Lincolnshire over the course of the next few days.  

 After leaving Pitsford, G393 passed through Buckinghamshire and Oxfordshire, passing over areas it had favoured during winter 2019/20, but now seemingly determined to return to the Isle of Wight. On the night of 7^th February G393 roosted in woodland just to the north of Newbury and, with a brisk north-easterly wind providing a helpful tailwind, set off again at around 09:30 the next morning. At 11:12 it was skirting the west side of Andover at an altitude of 298 metres and an hour later was over Stoney Cross in the New Forest. The Isle of Wight was now in sight and G393 crossed the Solent from Hurst Castle before making landfall just to the west of Yarmouth at 13:13. It had returned to the Isle of Wight exactly 17 months after first departing. 

 Once back on the Isle of Wight, G393 immediately located the other released birds and spent time at various sites around the Island. Interestingly local photographer, Ainsley Bennett, captured the first indications of territorial behaviour when he observed G274, who has remained on the Isle of Wight almost exclusively since release, chasing the rival male. 

On 28^th February, G393 crossed the Solent once again and skirted around Bournemouth to Poole Harbour. It remained in the local area until 6th March, favouring an area to the south of the harbour where it was been observed feeding on rabbits. Poole Harbour is within the likely settlement area of the translocated birds, and could certainly support breeding White-tailed Eagles in the future; so we hope this is a sign of things to come. G393 subsequently flew west to Chesil Beach on 6th March and then spent a day inland, before heading across Poole Harbour and then Bournemouth back to the Solent on 8th. Next day it headed across Southampton Water and then north-east past Petersfield. At 13:20 it was circling near Selborne, before turning and heading south into West Sussex. The change of direction may well have been prompted by the sight of G408 heading north-east from the Isle of Wight because the two birds met up in the South Downs later in the afternoon (see below).

G274 and G324 

In great contrast to G393, G274 has remained faithful to the Isle of Wight since release and it has been encouraging to see how this 2019 male has become increasingly adept at catching live prey during this period. G274, like other juveniles survived predominantly on carrion during its first winter, however from spring 2020 became adept at catching fish around the coasts of the Isle of Wight. In spring and summer 2020 Grey Mullet, which are abundant in shallow estuarine waters around the Island, became a favoured prey item, and the bird was also observed catching Black Bream in the Solent.  As autumn turned to winter we expected fish to constitute a smaller proportion of the diet, but G274 continued to catch fish throughout this period, particularly off the south coast of the Island at Blackgang. The satellite tracking data showed that between 1^st November and 9^th February G274 foraged off the south coast on 32% of days, flying up to a maximum of 4.5 km offshore. It was observed catching Bass on a number of occasions, including by two local crab fishermen from the boats. Bass are attracted to a shallow shelf off the coast at Blackgang by large numbers of smaller fish, and here they are relatively easy targets for hunting White-tailed Eagles. G324, another of the 2019 birds, was also observed catching fish in this locality throughout the winter.   

Since early February G274 has favoured another coastal site on the Isle Wight. Here it has been observed catching fish as well as Coot on a number of occasions and also an injured Canada Goose. Coot are a key prey item for White-tailed Eagles in the Netherlands and other parts of Europe and are likely to be important as a breeding population of White-tailed Eagles becomes established on the South Coast of England. Similarly, the goslings of feral geese are taken in substantial numbers in the Netherlands, but adult Greylag and Canadas are altogether more difficult due to their size. However, any sick or injured individuals may occasionally be taken as prey, as G274 demonstrated.

G324, meanwhile, has been observed catching Black-headed Gulls at another coastal site on a number of occasions, and is also regularly seen in the company of seals. In this case it seems to have learnt that seals often push fish close to the surface, and into White-tailed Eagle range. This clear switch from a dependence on carrion during winter 2019/20 to fish and other live caught-prey this winter is an extremely encouraging sign for the future, and illustrates the high prey availability for White-tailed Eagles in southern England throughout the year. 

G318 

It is clear from previous research, and our initial findings, that White-tailed Eagles can be highly individual in their choice of prey. This is exemplified well by G318, who has become something of a lagomorph specialist since release. This 2019 female spent five months during spring and summer 2020 in the North York Moors, favouring areas with high Rabbit abundance. Then, in late September, when it headed south into Lincolnshire, G318 again gravitated towards areas where Rabbits and Brown Hares were numerous.

G318 remained in Lincolnshire throughout the winter, frequenting quiet areas of the Lincolnshire Wolds where it was frequently observed catching both Rabbits and Brown Hares. Although the bird remained relatively sedentary during this period and spent the majority of her time perched inconspicuously on the edge of quiet woodlands, G318 did wander more widely on occasions, and was seen in a number of different localities around the county, including Kirkby Moor and nearby Kirky Gravel Pits as well as Middlemarsh Farm, where it was photographed by Nige Lound. 

Apart one brief return flight south to Northamptonshire (as described above), G318 remained in Lincolnshire until 27^th February when it made a purposeful move to the south, passing to the east of Boston at 13:20 and then across the north side of Peterborough at 15:20. It eventually settled in woodland on the Cambridgeshire-Northants border having flown 107 km (67 miles) from the Lincolnshire Wolds. G318 continued to head slowly south over subsequent days, and spent a night at Linford Lakes on the outskirts of Milton Keynes, on 2nd March.

After two days in southern Northamptonshire, north-easterly winds encouraged G318 further south and it flew 66 km (41) miles to south-east Oxfordshire that day, passing over Farmoor Reservoir just after 11:00 and eventually roosting close to the Wiltshire and Buckinghamshire borders. The next day G318 continued for a further 84 km (52 miles) south-west through Wiltshire, passing Amesbury and then Salisbury before crossing into eastern Dorset and roosting to the west of Verwood.

G318 has remained in the local area since, but it seems only a matter of time before she returns to the Isle of Wight after almost a year away.

Diet of 2019 birds

After more than a year-and-a-half of careful monitoring we are building up detailed knowledge of the diet of the 2019 birds since release. This is summarised in the table below.

Prey item	When taken	Comments
Marine fish, particularly Grey Mullet, European Bass and Black Bream	Year-round	Grey Mullet frequently caught in estuaries around coast of Isle of Wight; Black Bream and European Bass around IoW coast
Common Cuttlefish	Summer	Caught by G274 in seagrass beds in the Solent during summer 2020
Lagomorphs – Rabbit and Brown Hare	Year-round	Movements of 2019 birds strongly influenced by lagomorph abundance, with birds only favouring inland areas away from water where Rabbits and Brown Hares present in good numbers
Black-headed Gulls	Year-round	Key prey item throughout year with adults and fledged juveniles taken, but no evidence of birds predating colonies of breeding gulls (which are also avoided in Netherlands/Denmark)
Waterbirds, particularly Mallard and Coot	Year-round, particularly winter	G393 wintered along Oxon/Bucks border where large numbers of Mallard and also Wigeon present. Mallard feathers/remains found at regular roost site. G274 observed catching Coot on IoW
Carrion including scavenged waterbirds and gamebirds, dead fish and washed-up marine mammals, also kleptoparasitism of other species	Winter	High prevalence of dead/injured gamebirds provided abundant carrion for first-winter birds. Less important for older birds.
Corvids	Year-round	Corvid feathers/remains frequently located at regular roost sites
Wood Pigeon	Year-round	Wood pigeon feathers/remains frequently located at regular roost sites. May have been caught live or picked-up dead

Sit and wait

The satellite tracking data has also given us a valuable insight into how the birds live in the landscape. The GPS transmitters log the location of each bird as regularly as once every two-three minutes during the summer months (when battery voltage of the solar-powered transmitters is highest) and also record whether the bird is moving or stationary at the time. A recent analysis of these data show that the birds are perched for more than 90% of diurnal time. This is summarised in the table below for the three 2019 with the highest temporal resolution data. These findings corroborate previous research on White-tailed Eagles that demonstrate that they prefer the ‘sit and wait’ method of searching for food. For example a German study showed that they spent 93.2% of diurnal time perched. It is this habit of remaining stationary for long periods, often in quiet localities, that means the birds can be remarkably unobtrusive in the landscape.

	G393 (m)	G274 (m)	G318 (f)	Mean
Number of days	487	487	488
Total daytime GPS fixes	73799	60565	25763
Total GPS fixes perched	67435	54410	24187
Percentage perched	91.4%	89.8%	93.9%	91.7%
Total GPS fixes flying	6364	6155	1576
Percentage flying	8.8%	10.2%	6.1%	8.3%

2020 birds   

Whereas the 2019 birds have reached a stage in their development when they are more likely to remain on and around the South Coast, the 2020 contingent are now in the peak of the exploratory phase. Three of the remaining six birds from the 2020 release (G454 was sadly killed after flying into a powerline on the Isle of Wight in September), had already made exploratory flights away from the Isle of Wight during autumn 2020. G471 and G463 both flew west to Land’s End during October, and each bird subsequently wintered in the South-West – G471 on the Cornwall-Devon border, and G463 near Chard in the south of Somerset. 

G463

During the winter G463 lived in a relatively large core area of 140 km², predominantly to the north and south-west of Chard. This area included Chard reservoir where it was seen on a number of occasions.

In early February the young male began to range further and flew to the north Somerset coast just to the south of Burnham-on-Sea on 4^th February. G463 then lingered to the south of the village of Mark in the Somerset Levels until the afternoon of 7^th February when it returned to the Chard area. Then, on 10^th March, G463 headed south-east to the Devon coast near Bridport. It remained there all day on 11^th February, but then flew north on the afternoon of 12^th and spent all day on 14^th February in and around Copley Wood to the north of Somerton in central Somerset.

South-westerly winds on 15^th and 16^thFebruary  encouraged G463 to continue north-east and over the course of the next two days it flew 120 km (74 miles) across Somerset, and Wiltshire to West Berkshire. It lingered between Newbury and Reading for two days on 17^th and 18^th before making a brief visit to Theale Lagoon just to the south-west of Reading during the morning of 19^th.  G463 then skirted around the west side of the Reading, before spending the rest of the day in the Thames valley just to the north of the city. 

G463 moved further north on 20^th and lingered in the Chilterns in south-east Oxfordshire for three days before making another concerted move to the north-east on 23^rd, flying 86 km (53 miles) through Buckinghamshire and then Hertfordshire before roosting in woodland two miles east of Baldock.  Next day it flew a further 49 km (31 miles) further north-east into Cambridgeshire before covering another 47 km (29 miles) on 26^th, skirting to the east of  Newmarket and then crossing into north-west Suffolk. It lingered to the south-west of Thetford for two days before heading further north into the Brecks in Norfolk on 28th.

After a week in the Brecks, G463 flew a 105 km (65 miles) circuit to the North Norfolk coast on 7th March, flying over Blakeney, Salthouse and Kelling between 12:40 and 13:10 before heading back south-west.

G471

Like its compatriot from 2020, G471 spent the winter in the South West, spending much of its time on the Cornwall-Devon border. Its core area encompassed approximately 22 km² between Bude and Holsworthy, but on occasions the bird did make longer exploratory flights into other parts of Cornwall and Devon.

The most significant explorations occurred from 17th January, when G471 initially flew east to Toniton in Devon, at which point it was just seven miles to the west of G463. It then crossed the border into Somerset on 18^th before heading further south, skirting the east side of Dartmoor National Park and reaching the south Devon coast near Dartmouth at 12:30 on 22^nd January. It subsequently returned north and eventually returned to its favourite area on 1^st February.    

G471 flew to the north Devon coast near Clovelly on 14^th February and then, after a brief return to the Bude/Holsworth area on 16^th, headed east. It roosted in Stoke Woods just north of Exeter on  22^nd February, before flying 53 km (33 miles) north-east the next day to the Quantock Hills. It spent the day a mile north of Hawkridge Reservoir on 24^th and then flew north to the coast the next morning, passing just to the south of Bridgwater Bay and then heading purposefully east. By 2pm G471 was over Salisbury Plain and that night it roosted in a small woodland near Tilshead after flying 97 km (60 miles) during the day. 

We wondered if G471 would linger on Salisbury Plain, as other White-tailed Eagles have done in the past,  but instead the young male followed the lead of G463 and continued to head north-east over subsequent days. It roosted just to the south of Burbage in Wiltshire on 26^th and was seen attempting to catch a Brown Hare the next morning. It headed off soon afterwards and flew a further 58 km (36 mils) to the Chilterns in south-east Oxfordshire, just as G463 had done. In fact that night G471 roosted 2 km south of where his compatriot had spent the night six days previously.   

G471 continued to follow the Chilterns ridge north-east over the next few days, passing directly over Tring at 13:46 on 1^st March and crossing into Bedforshire later that afternoon. It subsequently roosted in a small wood between Dunstable and Leighton Buzzard that night before slowly making its way north through Bedfordshire over subsequent days, finding quiet woodlands to roost in each night. The similarity of the flights of G463 and G471 through the Chilterns is striking and demonstrates the importance of both wind direction and geographical features in shaping the exploratory flights of the young eagles (see above).  

On 5th March G471 crossed the border into Cambridgeshire and arrived at Graham Water shortly after 09:00. The young male was subsequently observed catching a trout later that day, and it has remained at the reservoir until the morning of 9th March, providing great views for local birders and members of the public. It was seen attempting to catch fish again on Saturday and then feeding on a Black-headed Gull on Sunday.

G461

G461 was the first of the 2020 cohort to the leave the Isle of Wight, completing a two-week round trip to East Sussex in early October. The young male then remained on the Isle of Wight until 5^th February when it crossed the Solent from the Needles and then spent two days in the Avon valley midway between Christchurch and Ringwood. It crossed Bournemouth and Poole Harbour on 7^th February and roosted that night close to Abbotsury Swannery in west Dorset. It continued to head west the next day, passing Bridport at 09:00 and then the Exe estuary at 11:00. It then followed the coastline south-west and was close to Prawle Point at 12:00. It eventually settled in a wooded area near Mothercombe at the mouth of the River Erme having flown an impressive 138 km (86 miles) in just over five hours of flying.

G461 remained in Devon until 7th March, favouring an area of 25 km² centred around the Erme and Yealm estuaries. Encouragingly it was observed catching a fish on at least one occasion, indicting the young male is following the lead of G274 and G324 on the Isle of Wight by learning to exploit the rich food availability in South Coast estuaries.   

After just under a month in Devon G461 was on the move again on 7th March, initially flying south-east to Prawle Point and then 50 km north to a small wood 7 km south-west of Exeter. Next morning the young male set off north again at first light, skirting around the west side of Exeter, before heading north-east into Somerset. It passed to the south of Taunton at 13:00 and then spent the afternoon at West Sedgemoor RSPB reserve having flown 68 km (42 miles). G405 remained at West Sedgemoor until 13:30 next day when it headed north-east. It was subsequently seen at Ham Wall and then to the west of Frome, before roosting within a mile of G405’s roost the previous night (see below).

G405

G405 remained on the Isle of Wight throughout the winter, and then crossed the Solent for the first time on 10^th February. The young female crossed the eastern New Forest, before turning west and roosting in woodland near Ashmore in east Dorset, having flown 88 km (54 miles) from the Isle of Wight. Next day G405 headed 26 km (16 miles) further north into Wiltshire and subsequently settled at Longleat Safari Park where it remained for the next two weeks, favouring an area of 6 km² and roosting in the park most nights.

On 26^th February G405 set off wandering again and next day flew purposefully south-east, passing over Winchester at 13:45 and then to the north of Chichester at 15:30. It eventually settled to roost in woodland to the east of Arundel in West Sussex, having flown 128 km (80 miles). Next morning G405 continued east along the coast and at 11:25 was photographed over Lewes by Brian Cox. Just over an hour later it was circling 10 km to the north-east, but then turned and headed back west along the coast, passing just to the north of Brighton, Worthing and Bognor Regis. It then skirted north past Chichester Harbour before roosting in Singleton Forest in the South Downs after a day’s flight of 137 km (85 miles).

On the morning of 1^st March G405 headed off north-west, passing to the north of Winchester at 12:45 and then across the southern part of Salisbury Plain, before returning to Longleat. G405 had flown another 112 km (69 miles), meaning its three day flight totalled 377 km (234 miles); another good example of one of the young eagles starting to learn the landscape of southern England. 

G405’s explorations did not stop there because on 8th March it flew north, passing over the west side of Bath just after 13:00 before reaching the Severn estuary just after 14:30 when it was circling just to the north-east of Slimbridge WWT. It subsequently returned south again and eventually roosted in a wood in north-east Somerset having flown 134 km (84 miles). It then returned to Longleat the next morning.

G466

G466, another female, also remained on the Isle of Wight throughout the winter, often in the company of other juveniles and the three 2019 birds. On one notable occasion it was photographed by Owen Cass while perched in a tree with G408 and G274.

On 1^st March G466 crossed the Solent for the first time in the company of 2019 male, G274. The two birds roosted together in the New Forest near Furzey Lodge. While G274 returned to the Isle of Wight next morning, G466 continued north across the New Forest and then into the Test valley. It spent several days to the south of Stockbridge and then, on the morning of 6th March, headed east, passing to the north of Winchester at 09:30, and then south through the western South Downs. By 11:38 it was over Lee-on-Solent at an altitude of 518 metres and then crossed the Solent back to the Isle of Wight having flown 68 km (42 miles). It has since been seen back in the company of G274, G324 and G408.

G408

G408 was the last of the 2020 cohort to venture away from the Isle of Wight. In recent weeks this young male had been a frequent visitor to the wetland sites favoured by the 2019 birds, and Project Officer Steve Egerton-Read also saw it catch a Rabbit in an area often visited by G274.

G408 finally ventured across the Solent on 9th March, crossing from the Isle of Wight coast just north of Bembridge to Southsea, between 12:24 and 12:39. It then crossed Farlington Marshes before heading north-east into the South Downs where it met up with G393 who had spent the night on the north shore of the Solent before moving into the South Downs.

Other White-tailed Eagles

We are very grateful to everyone who has reported sightings of White-tailed Eagles over recent months, many of which relate to birds from the Isle of Wight. However, at least three-four of the birds seen recently are likely to have originated from Continental Europe, or Scotland. An immature White-tailed Eagle seen at the Blyth Estuary in Suffolk on 27th and 28th February was definitely not one from the Isle of Wight, and probably a wandering individual from the increasing population in the Netherlands. Similarly one seen over London on 6th March, and probably the same individual over Lewes in East Sussex the next day, is also likely to have been a wandering bird from the Continent. Another immature over Knaresborough in North Yorkshire on 2nd February, and one at Flamborough on 6th and then nearby Fraisthorpe on 8th and 9th March were also birds that originated from either Continental Europe, or Scotland.

While these wandering birds are likely to return to their natal areas, our hope is that as a breeding population becomes established on the South Coast, some will eventually remain to breed if they encounter unpaired birds from the Isle of Wight.

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