A shocking decline in the number of swallows in Nova Scotia has scientists and bird watchers stumped.

Not long ago, several different species of swallows could been seen all around the province but now they are few and far between.

Blake Maybank has spent about 20 years watching the birds in the province.

"Swallows in particular, but among other species, I notice their population changes. And with swallows, all of their populations in Nova Scotia and across the Maritimes are in a steady, long-term decline," he said.

Maybank says one of the species, the purple martin, no longer breeds in Nova Scotia.

Four others, including barn swallows and tree swallows, have seen declines ranging from 60 to 98 per cent.

In 2013, dwindling numbers forced the province to add barn swallows to its list of protected species.

"It may be an impact of climate change in a way that we don't understand. It may be insecticides, pesticides — we don't know the answers, there's not enough research being done," he said.

"It's really quite scary."

But Tara Imlay, a Dalhousie PhD candidate studying the birds, thinks their scarcity might have to do with the insects they're eating.

"I'm curious to find out whether or not these populations have declined as swallows are also declining, or if maybe, when insects are most abundant is no longer synced-up with when the swallows are breeding," she said.

Imlay is now analyzing the abundance of insect, feather and blood samples she collected this summer, hoping soon they will have an answer as to why the swallow populations are dwindling.