The answer is food. “There is a lot of marine algae in Dublin Bay but not enough … As that runs out they start to come onto the football pitches.”
It was sometime in the early 1970s when Dublin’s brent geese started to move and graze inland, says Stuart Bearhop, a professor of animal ecology at the University of Exeter.
Before that, the seabirds stayed mostly at sea. “The classic picture is they would be on the salt marsh at high tide and then in amongst the seaweed at low tide,” he says.
Brent geese are protected as part of the Dublin Bay Special Conservation Area, so their decision to move inland can affect development plans for homes and all-weather pitches and all manner of things – if the building risks removing their new feeding grounds.
Ideally, the geese would prefer to live on marine algae, says Bearhop. But after that stretch of good years, their numbers are so large so each winter they run out of that food, he says.
“There is a lot of marine algae in Dublin Bay but not enough to support the population as it now stands,” Bearhop says. “As that runs out, they start to come onto the football pitches.”
The geese have spread further inland in more recent times, too. Martin Quinn, a wildlife enthusiast who lives in Lucan, says they started to visit his area in large numbers during the first winter of the Covid-19 lockdown.
Developers, sports clubs and others point out that there is a lot of alternative green space in the city the geese could go to – and leave theirs alone, says Bearhop.
But not all of that is suitable for geese, Bearhop says. “Although there is lots of green space, it’s not clear how much of that they could use.”
In March, Dublin City Council planners refused permission for 330 homes and 60 “assisted living units” at the former Cadbury’s Pitch and Putt site on Oscar Traynor Road in Coolock.
Among the reasons cited was a failure to show that building on the site wouldn’t badly affect brent geese.
The birds weren’t the sole reason for rejection. The plans were also knocked back because the development wasn’t in line with the zoning and the developer had failed to meet standards for daylight for homes in two of the blocks.
But also in March, plans for an all-weather pitch in Ashtown stalled because of concerns about the geese. The Department of Housing told the city council that it needed to look at the cumulative effect of plans to convert playing pitches to astroturf.
In March 2022, the High Court quashed permission for a controversial development of 580 homes, at St Anne’s Park in Raheny because the site is important for the birds.
As they spread out across the city and its suburbs, brent geese could impact even more plans.
Quinn says that before the Covid-19 lockdowns, he never saw brent geese in Clondalkin. Then, in the winters of 2020 and 2021, they flocked there.
That came as a big surprise, he says. “It happened overnight. People couldn’t believe it was happening. They were massive numbers.”
Quinn sent a video taken in February 2023 of a big gaggle of brent geese feeding on grassland near the Fonthill Retail Park in Clondalkin.
Before lockdown, he had never seen them further inland than Drimnagh, he says.
Each summer, light-bellied brent geese take flight from their mating grounds in the Arctic in Canada, refuelling and resting in Greenland and Iceland for a couple of months, before arriving in Ireland each October.
Around 98 percent of the global population flock to Ireland, says Helen Boland, the Dublin Bay birds project manager with Birdwatch Ireland. They thrived in Dublin Bay until just a few years ago, when their numbers also started to fall, she says.
On a recent Friday afternoon on Bull Island, around 100 brent geese idle on the marshland, some peck at the ground. A group of around 20 birds whoosh into the air and land again nearby.
In the coming weeks, these birds will leave Ireland for the summer on the 3,000-mile journey, hopscotching to the Arctic in Canada. Comparatively, the trip from Dublin’s coast to Clondalkin is akin to a stroll to the shop.
Still, the birds would be better off at sea, says Bearhop. Brent geese prefer to feed mainly on marine algae and it’s better for them, he says.
“The marine protein in their diet is correlated with how much fat they can put on and actually whether they have chicks the following year,” he says.
The algae grows in summer and as winter wears on, it starts to run out, he says. That is when the birds move onto other green spaces – and they particularly like playing pitches.
When the geese look for new grasslands to feed on, they like to go back to the same places over and over, says Bearhop. “They are creatures of habit.”
It isn’t always obvious why they select a specific site, he says, but the factors likely include “how easy it is to take off, how many dog walkers there are, what kind of grass is sown on them”.
The geese like playing pitches because of the length of the grass. They graze on the tips of the grass which are nutritious and digestible, he says.
Would geese just move to other spots, if their favoured grassy areas are built on? That’s still unclear, Bearhop says.
“We don’t have a huge understanding of what drives the selection,” says Bearhop. “I think it’s quite likely they would move to other spots but we just don’t know.”
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