LONDON, ONT. -- Old chimneys collect dust and soot, but they’ve also become home for some of our feathered friends and sadly, the species is declining rapidly.

Birds called Chimney Swifts often choose chimneys on the top of old buildings as their nesting grounds.

A popular spot for the Chimney Swifts is at the First-St. Andrew’s Church in London, Ont.

The church has five chimneys, each currently occupied by a nesting pair of Chimney Swifts, one of the fastest flying birds in the world.

Wife and husband nature lovers, Winifred and Dave Wake, have been following these tiny but fast birds, often setting up camp at the church to watch them from a distance.

"Look up, way up, they’re like tiny flying cigars with rapidly beating pointed wings that are constantly changing directions," says Winifred, who is also the Chimney Swift liaison for the Nature of London organization.

Winifred says she took a liking to them after discovery some of their unique quirks.

"They fly high overhead and they only eat insects they capture on their wings, and they nest inside chimneys because they’re not able to land or perch on the ground of rooftops. They perch inside the chimneys like a woodpecker would, and they make a nest inside the chimney with twigs they glue with their own saliva."

The Chimney Swifts haven't always called chimneys home. Before big buildings took over, they would make their nests in native hollow trees.

The sad news is, the Chimney Swift is declining in numbers.

In 2009, the species was considered threatened and at risk for extinction.

“In the last 70 years or so, their numbers have declined by 90 per cent in Canada and Ontario.”

Swifts migrate each spring and fall, with their wintering grounds in South America.

“An examination of historic and current records provides hints as to the pattern of swift decline in southwestern Ontario over the years,” the Nature London website explains.

Winifred says theres two main reasons for their decline -- one is lack of food.

Insects may be a pest to us but they are a lifeline for Chimney Swifts. They can eat a thousand bugs a day per bird.

Insects are on the decline due to woodlands being turned into building complexes. Drivers are also a big contributor to the decline of insects -- with bugs hitting windshields on highways.

And places to nest are becoming few and far between, as hollow trees are already limited and old chimneys on old buildings are being demolished.

Winifred says if you want to help this threatened species, you can start by planting some native plants and trees in your backyard to grow the insect population.

She also encourages people to support organizations that preserve wetlands and conservation areas.

If you want to learn more about the Chimney Swift, click here.