Ontarians should expect to see fewer monarch butterflies in the province than they usually do, after a rainy spring delayed their journey northward and saw fewer of them make it across the border.

Monarch butterfly trail being built in Leamington

Chip Taylor, the director of Monarch Watch at the University of Kansas, said the spring weather south of the border was tough for monarchs.

One issue was that there was too much rain in Texas and Oklahoma, which Taylor said meant that monarchs weren't able to move on as many days as they otherwise could have.

A second issue was colder temperatures, which restricted the number of monarchs heading north and northeast.

"So, the result was that we had fewer monarchs reaching Ontario on time and fewer in total reaching Ontario and this will result in both a late migration and smaller migration out of Ontario and the northeastern United States," Taylor told CBC News in a telephone interview from Alaska on Tuesday.

Taylor said the overall number of monarchs will be down in Ontario, though hard numbers aren't possible to come by.

"I think normally you would expect to see something two to three times what you're probably going to see this year, but I can't give you actual numbers, in terms or thousands or millions of butterflies," he said.

"On a relative scale, the population is going to be down. That's all I can tell you."

Loss of habitat

Taylor says a combination of factors have caused the decline of the monarch population.

"You're looking at an accumulation of things. It's not just one thing," he said. "You're looking at a history here. You're looking at some weather factors and the long term habitat loss that seems to be perpetuating rather than reversing."

Vic Bernyk owns Native Trees and Plants Nursery in Amherstburg, Ont., south of Windsor. He specializes in butterfly habitat.

Bernyk says the decline is partially caused by the loss of native habitat, milkweed in particular.

"They're running across issues of trying to find suitable plants for reproduction because one of the things that's happened over the last several decades is there's been a continuous loss of habitat for monarchs to supply the plants that are needed for reproduction," Bernyk said.

Monarch butterflies will lay their eggs only on milkweed plants. Milkweed is also the primary food source for monarch caterpillars.

To increase the amount of milkweed available to monarchs, a monarch butterfly trail is being developed in Leamington in an effort maintain and even boost monarch butterfly population.

Leamington is home to Point Pelee National Park, the final stop for monarchs during their fall migration south to Mexico. The migration is a huge tourist attraction for the park.

Several requests for interviews were made with Point Pelee staff.