There is only one thing more terrifying for a nesting bird than a person walking nearby: when that two-legged beast is joined by a four-legged companion. A study of how ground-nesting birds are disturbed on beaches in Spain has revealed how they are almost always scared from their nests by passing off-lead dogs, but seem unperturbed by motorbikes, helicopters and low-flying planes. Walkers accompanied by dogs flushed Kentish plovers from the foreshore nests 80% of the time when walking on paths over the beach, compared with just 12.9% of the time when without a dog. When walkers with dogs did not stick to paths but roamed the dunes, they scared the plovers from their nests 93.8% of the time. The study by Dr Miguel Ángel Gómez-Serrano of the University of Valencia found none of the 714 nest disturbance events observed on four beaches in Castellón and Valencia involved dogs on leads. “Fewer and fewer beaches have the capacity to host coastal bird breeding populations, so we should be concerned about conserving them,” said Gómez-Serrano, who called for dogs to be banned from more beaches during nesting season. “Dogs produce a disproportionate impact compared to that of people walking on the beach, so their entry into these areas should be limited at least in the most critical [breeding] season for these species. At this time, birds are incubating their eggs or guarding their chicks, and cannot change beaches to avoid disturbance.” The Kentish plover is a small, declining shorebird that lays camouflaged eggs on beaches across southern Europe. In Britain, similar shorebirds such as ringed plovers, oystercatchers, and little, common and sandwich terns nest on beaches. The ringed plover is on the “red list” of Britain’s most endangered birds. Its population fall of 37% between 1984 and 2007 partly attributed to nest disturbance as beaches become busier. While cordons are erected on some British beaches in spring to encourage walkers to keep off small areas of sand and shingle where birds nests, the string rarely keeps out dogs. Nesting birds will abandon their nests if disturbed too often, or their eggs may become too cold or too hot to hatch. Plover eggs have been found to tolerate temperatures between 15C and 42C before the embryo dies, with eggs rapidly overheating in Spain if left in direct sunlight without the bird sitting on them. The study, which was published in Ibis, the international journal of avian science, found that on busier beaches the flushed birds returned more quickly to their nests, suggesting they could become habituated to humans nearby. But with dogs banned from busy urban beaches in Spain during the holiday season – as is also the case on many British beaches – Gómez-Serrano said there were now more dogs being taken to remote, wildlife-rich beaches for exercise. Mark Cocker, a naturalist and author, said: “We’re in denial. We know dogs are genetically wolves and we have 10 million of them in this country. There’s clearly an environmental issue, but conservationists are scared of talking about it because it’s such a strong lobby. It’s about dog-owners showing restraint and understanding they are part of a very large cohort of people and the privilege of owning a dog comes with responsibilities. “It’s not about excluding dogs from beaches or public spaces but acknowledging that dogs off leashes cause significant problems. Dogs could easily be kept on a lead between the months of March and June when birds nest. For eight months of the year, they wouldn’t be interfering with birds’ reproduction on the beach and there should be no conflict.” Asked whether keeping dogs on leads during the spring breeding season would help nesting birds, Gómez-Serrano said: “Although the roaming movements of dogs are more reduced when on lead, dogs trigger an anti-predatory instinct in birds not comparable to that of humans. “In addition, unfortunately dog owners do not usually comply with the regulations about dog walking on leads, so surveillance is necessary so that these regulations are respected. Obviously, there is usually not enough budget for this purpose, and managers prefer not to address this widespread problem in coastal areas.”