Two juvenile Montagu’s Harriers were fitted with satellite tags in late July, the first juveniles of the species to carry one in the UK, according to the RSPB. By 3 September the RSPB had logged a three-hour crossing of the North Sea by one of them. It had recovered the body of the other along a railway line.

Both birds hatched this summer to the same father. Everything below is his line.

AU hatched in Wiltshire in 2016

He came out of a nest of three. His own father was a partly melanistic bird named Mel, and the chick was given a colour ring inscribed AU, which is what the fieldworkers have called him ever since.

He first bred in 2018 and has raised at least sixteen juveniles. He is, in the RSPB’s words, “the only adult male Montagu’s Harrier known to be breeding in the UK currently”.

That sentence carries more weight than it looks like it should. The RSPB records a recent peak of nine successful nests in 2011, and no pairs at all between 2020 and 2023. The UK breeding population’s high point, roughly 30 pairs, was in the 1950s. Pairs bred successfully in 2025 and again this year, and both years have run through AU.

Two females settled with him this spring

A fieldworker the charity paid to watch the same ground from mid-April found him skydancing, and the display ran ten days. The RSPB had been watching that ground because three local birders contacted its hotline in 2025 with sightings that led to the confirmation of a breeding pair.

Two females stayed. One was CV, colour-ringed in July. The other was unringed, thought to be three years old, and the fieldworkers called her “bronze”. Each raised three chicks, at two nests roughly a kilometre apart at a location the charity will not name.

One of those nests sat inside a patch of barley the farmer left standing as habitat. Two of the RSPB’s photographs are captioned as a juvenile on the protective fence that surrounds her nest.

FH and HV

FH is CV’s daughter. HV is bronze’s, and is named in memory of the ornithologist Harry Vilkaitis, who died in 2025. They are half-sisters, and in late July each was picked up out of her nest, a few days before her first flight, and given something the RSPB says no juvenile of the species had carried in Britain before.

The obstacle was weight. Best practice holds that a tag should not exceed 3 percent of a bird’s body mass, juvenile females tend to weigh around 360 grams, and until recently the hardware was too heavy to fit inside that. The tag they carry weighs 5 grams, which the RSPB describes as well under the threshold. “Only now that the tags are light enough can we fit them to juveniles,” says Jack Ashton-Booth, the charity’s tagging expert, who says “The biggest mystery is their childhood.”

Each unit costs 3,000 pounds, sits on the bird’s back like a rucksack on Teflon straps, and runs off a tiny rechargeable solar panel. Argos satellites relay the positions.

HV went to sea

On the night of Sunday 30 August she roosted at the RSPB’s Frampton Marsh reserve in Lincolnshire.

The next morning she flew south-east into Norfolk, passed south of Norwich and reached the Suffolk coast near Covehithe. The team expected her to turn south down the coast. She went out over the water instead, on a direct flight of about three hours at around 33 mph, made landfall near Rotterdam, and roosted near Eindhoven. The charity’s published response was “We are amazed! There is more to come we are sure!”

Her species covers a roughly 3,500-mile journey to its wintering grounds, and, by the RSPB’s account, no British-hatched juvenile had ever carried a tag onto one.

As of the charity’s 3 September update, HV had passed through Luxembourg and was just inside France, with the RSPB asking whether she will continue south and avoid the Alps.

FH got as far as a railway line

Her tag began reporting a cold temperature, which the team read as indicating she was probably dead. The data also suggested the tag was moving rapidly between two locations around 30 miles apart, and those two points matched a west-to-east railway line.

She had been struck by a train and carried along the route. With the help of staff, the team located and recovered her body. The tag was still in perfect working order, and it is what led them to her.

That is the whole return on one of the two tags: a cause and a place, and no migration at all. It is worth setting against the 2014 season, when adults were tagged in Britain for the first time. Some of those tags ran for years and documented migratory routes that stretched further south than scientists had previously thought. Others stopped transmitting, which the charity attributes to likely persecution, and a tag that goes silent without a temperature reading and a rail line beside it does not explain itself.

So the season’s evidence is two birds, from two nests, fathered by one male, one of them dead by early September. Mark Thomas has been the RSPB’s Montagu’s Harrier species lead for the past twenty years. He set the limit before either result came in: the tagged chicks “may not be representative of all juveniles, but they can still offer answers, particularly as to when and where they return to Britain”. HV’s crossing is one juvenile’s crossing. Whether young British Monties routinely leave via the Suffolk coast and the Low Countries is not answerable from her, and the charity’s own word for the flight is “unexpected”.

Three of last year’s are already back

JP was seen at his hatching site in May. JJ was photographed in Oxfordshire in July. JO was seen back at her nest site in July. All three came out of AU’s 2025 nest, and the RSPB says each may return to breed in 2027.

Back to the barley

The RSPB expects the male to be the last of them to leave: the females first, then the young, then him, off the same ground he was skydancing over in April, in a season that produced six juveniles from a species that produced none at all in Britain four years running.

He hatched in Wiltshire in 2016 from a nest of three, and one of the six he fathered this year is already dead along a railway line. The tags were fitted to find out what happens to young Monties once they leave the nest. For one of the two, the answer arrived by 3 September, and faster than anyone wanted.

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