Having seen peaks as high as 1,700 attempts at the start of the month, there were only 149 bids to enter the tunnel on Sunday night and 130 the
previous night, the sources said.
"It's the result of supplementary security measures, building work and reinforcements from both states," said a Eurotunnel spokesperson.
An extra 120 police were sent to the Calais site in northern France in late July, adding to the existing 300 police and 200 Eurotunnel guards.
New wire fences have also been installed around the entrance for vehicles boarding Eurotunnel trains, where migrants generally try to break in.
Aid groups have also emphasised that the situation is simply returning to normal after an exceptional period.
The migrants had taken advantage of the chaos caused by strikes around the nearby ferry port, which had forced many more trucks to use the Eurotunnel and putting the strain on security systems.
The lack of crossings also means that more migrants are stuck in Calais and unable to reach Britain, said Francois Guennoc, secretary of a local aid group for migrants, estimating that numbers at the camps would rise to around 4,000 by the end of August.
"There are less people trying to get into the tunnel, first because they know it's dangerous, and also because there are more police," said Guennoc.
Between nine and 12 migrants are thought to have died this summer trying to reach Britain.