The term vagrant, or accidental as they are sometimes known, are those birds who have inadvertently ended up somewhere where we think they didn’t intend to be, out of their normal range, far from home.  Or so the view has been for many decades.

It has long been thought that birds who were observed away from where they “should” be were either unlucky, are juveniles and inexperienced of the challenge, or perhaps even faulty in some way. Storms and gales and even hitch-hiking on ships can account for many birds out of place, but there have been theories that those found far afield when no such weather event or transport was present may “just not work properly”.

The mechanisms of migration are still quite poorly understood – the theories are in all likelihood correct, but little proof actually exists to show that birds can definitely remember constellations and navigate using the stars, or have a magnetic alignment in their skulls, or some code is passed on through genetics.

Imagine the thrill when an altogether unexpected bird arrives.

However they do it, there is no shortage of admiration for them, and twice a year, eager birders the world over wait in anticipation for their usual migrants to arrive. So, imagine the thrill when an altogether unexpected bird arrives, one you may have only ever seen in a book or online, and it just shows up in your back garden or regular walk through the woods.

In an English country garden

Data submitted by keen birders on platforms such as eBird and Birdguides.com is invaluable to those who wish to know where the latest rarities have landed; it is not unusual for people to descend upon a particular locale within hours once an especially exciting vagrant has been logged.

In January 2008, one morning retired vicar Richard Bending and his wife Sue spotted a peculiar looking sparrow-like bird nibbling seeds from their feeder in their garden in Cley, Norfolk, on the east coast of the UK. They consulted a library book and thought they had identified it but assumed they were wrong as surely that couldn’t have made it to their quiet little village.

They contacted a local birder who came over, and confirmed that yes, that is indeed a white-throated sparrow, normally found foraging under shrubs in the United States 3,000 miles to the west of their humble garden.

By mid-afternoon, the road outside the Bending’s home was chock-full of cars and bicycles as birders flocked to get a glimpse of this tiny grey and brown bird, it’s humbug striped head bringing panache to a bleak winter afternoon.

The couple moved the feeders to the front driveway to help visitors get a better look, and the bird stayed for two weeks, during which 4,000 people came by to take photographs.

The event was so unparalleled in the village that the residents and birders later had a whip-round and raised over £6,000 to commemorate the visit, and a suitably small stained glass rendering of the bird was installed during the renovation of the village’s 13th century church west window in 2010.

Accidently on purpose

Every birding community will have their tale told in hushed awe of the time that green heron dove off the edge of a boat, or the white-tailed eagle that landed near the car park, or the broad-billed hummingbird resting on an Ohio buckeye branch for a few days.

Sightings like this happen with middling frequency – that particular species of sparrow had been spotted in the UK at least twice before in the ‘70s and ‘90s – and some parts of the world make a living off the likelihood of vagrants appearing during migration season, with guided tours held in places such as the Alaskan archipelago, Newfoundland, and in the Wet Tropics, the northeast coast of Queensland, Australia, where vagrants are annual occurrences in all of these places and more.

Inevitable links to climate change have already been made.

Whilst many of these birds will indeed have ended up there by accident, there is a growing view that some vagrant sightings are indicative of something else, something bigger, and maybe we need to pay a bit more attention after that first hastily taken photograph. These birds may not be so unlucky, green, or broken after all.

Now that information about vagrant sightings is becoming widely available and more and more people are contributing to databases, there are some scientists keen to link all that nomadic information and view it as a larger picture, potentially giving hints and clues to bird dispersal and emerging patterns across the world.

Vagrants are by their nature very hard to study as – at present at least – there are so few of them and they show up where you least expect them.

Inevitable links to climate change have already been made; as weather conditions change, birds that use the Central Americas flyway that crosses the Gulf of Mexico may be more likely to get caught in winds and flung across the Atlantic, ending up in Europe.

These observations also throw up the next logical questions.

Research has also been underway that has observed populations of certain birds expanding, notably those who exhibit nest parasitism, and covering greater ranges than their historical grounds.

Recent unusual temperature changes have led to irregular pressure variations, the result of one of which pushed a large high-pressure system over Siberia, increasing the surface temperature there by more than 20°C in January 2021.

Eurasian cuckoos such as the common and Oriental cuckoos have been frequently showing up much further north than their expected habitat in north-eastern Siberia, and can now be sighted within 300km of the Bering Strait. One common cuckoo pair has been seen mating in Alaska, and another sighted in California.

The cartography challenge

But these observations also throw up the next logical questions: where will these seemingly settling vagrants over winter, will they develop new flyways to get there, and how will the resident population adjust to territorial disputes from these unknown incomers?

It’s impossible to know if these questions are even relevant at this stage, but from what researchers have found from the information available so far, there is every reason to consider the answers.

With all this in mind, it may be that some of these birds will need a new name – “settler”, perhaps, or “coloniser”. It’s going to be interesting to see how many of these alleged hobo birds never leave their stumbled-upon home, how many then continue to join them, and how their presence literally alters the landscape.

One thing’s for sure, if vagrants are a sign of shifting populations, a lot of field guides are going to need to update those distribution maps.