The Cessna crashed Sunday during a routine flight to count birds. (CBC)

The two Environment Canada employees involved in Sunday's small-plane emergency landing on a Yarmouth County highway were counting birds.

The 26-year-old pilot is in serious but stable condition in Halifax's QE2 Health Sciences Centre after his plane landed on Highway 3 in Lower Argyle, ran into a ditch and hit an apple tree.

The two passengers aboard the four-seater Cessna 172 travelling from Greenwood to Yarmouth were treated for non-life threatening injuries, police said.

"Environment Canada chartered this flight to conduct routine coastal bird monitoring surveys in southern Nova Scotia coastal zones," Environment Canada spokeswoman Sujata Raisinghani said Monday. "These are done when the weather is near ideal for observations and yesterday it was sunny and calm."

The flight was chartered with Central Valley Aircraft Inc., based in Waterville, N.S., and flying from Greenwood to Yarmouth.

Raisinghani said the survey involves flying a small plane over coastal areas at slow speeds and an altitude of 40 to 60 metres to count numbers of birds at various times of the year. The surveys are done over the coastal areas of Atlantic Canada over a three- to five-year period.

"Wintering surveys are particularly important, as many birds which do not migrate farther south will winter in the open water marine areas of the Atlantic Provinces," Raisinghani said.

"The information collected gives indices of distribution of birds at various times of the year and is useful, particularly for environmental assessments and emergency response activities."

The names of the crash victims have not been released. Raisinghani said one of the Environment Canada employees had left hospital and the other remained in hospital as of Monday.

There is no update on that person's condition or the condition of the pilot.

Routine refueling

The Environment Canada staffers were based in Sackville, N.B.

"The good news from our perspective is that they're both fine. They've got some minor injuries and we hope to see them at home. It won't be today — it is a bit of a drive from Yarmouth to come back — but possibly tomorrow or the next day," said Doug Bliss, the regional director for Environment Canada's Canadian Wildlife Service.

"We do know that they had started about 7:30 in the morning, starting the surveys, and that they were approaching Yarmouth airport, I understand, to refuel the aircraft, which is typical. You have to do that once or twice during the course of the day when you're doing these kinds of surveys."

He said Environment Canada logs "tens of thousands" of hours in aircraft each year.

"We're quite used to this and will do a fact-finding after things settle down and determine if there were any issues."

The plane landed in front of Arley Spinney's house in Lower Argyle. He said the engine appeared to not be running as it descended.

The plane is being examined by investigators from Transport Canada searching for the cause of the crash.