On Sunday afternoon, the couple proudly showed off the fruits of their diligent efforts during a tour of their "bluebird trail" in Antietam National Battlefield, which is adjacent to their property.
The Raabes led 18 people in a caravan from box to box along Dunker Church and Smoketown roads.
Many were members of the Potomac Valley Audubon Society (PVAC), which sponsored the field trip.
Peeking inside the specially designed boxes, group members were able to glimpse the various stages of the nesting cycle - from tiny blue eggs laid within the past week, to just-hatched chicks gaping for a meal to a 15-day-old brood almost ready to leave the nest.
What they found matched Jean Raabes' records, updated during weekly checks throughout the April-through-July nesting season.
The couple said they have recorded more than 3,200 fledglings leaving the battlefield boxes since 1979, when park officials gave them permission to put out the first 40 boxes.
Over the years, that's grown to about 70 boxes, discreetly mounted on wooden fences and utility poles about 100 yards apart.
With 148 bluebirds fledged so far this year and a nearly equal amount of eggs and birds in the boxes right now, the Raabes said they're optimistic they'll top their record year of 221 fledglings.
"We're having a tremendous year," said Mark Raabe, who attributes it partly to favorable weather and partly to just-plain luck as far as sparrows are concerned.
While the holes into boxes are intentionally made too small for aggressive starlings to get in, the bluebird nests are still at risk of being attacked by sparrows as well as blacksnakes and raccoons, he said.
Sunday's tour was an eye-opening experience for PVAC member Vernon Patterson of Martinsburg, W.Va., who said he had spotted bluebirds in past visits to the park but never noticed the bird boxes.
Mary Ann Trumpower of Big Pool, Md., said she was thrilled to be able to see the just-hatched birds.
"I haven't seen them that young because I was always afraid if I messed with the box they wouldn't come back," said Trumpower, wearing a pair of dangling bluebird earrings. "I just love bluebirds."
Trumpower said she has been attracting the same pair of bluebirds to her yard every year by feeding them worms.
"They're so cute," said Nancy Garritt of Germantown, Md., after peering into one of the boxes .
Garritt was glad she missed the bike tour she had come to the park to take.
The Potomac Valley Audubon Society meets fall through spring on the second Wednesday of the month in the Grist Mill Classroom at the National Biological Service - Leetown Science Center in Leetown, W.Va.
The group will resume meeting at 7:30 p.m. Sept. 10.
For more information, call 304-876-2114 or 800-429-0406.