Bluebirds and tree swallows have much in common, including habitat and food sources. oth are also cavity nesters and have the same nesting requirements. In fact, with used woodpecker holes and good birdhouses being at a premium, these same birds will struggle and fight over the best nesting sites. To the victor belongs the spoil.
The winning pair will take over the nest box and quickly remodel it to their own specifications, including evicting all sign of the previous occupants. Eggs and even young birds will be thrown out in preparation for their own family.
This year, one box has been different. Bluebirds initially set up housekeeping, built the nest and laid three eggs. Then tree swallows came along and drove off the bluebirds, taking over the nest. However, the tree swallows did not destroy the eggs. The female tree swallow merely laid two eggs and began brooding as usual.
All of this brings up many questions.
Will the bluebird eggs hatch?
Will the tree swallow take care of and adopt the young blues, possibly at the expense of her own young?
Is this a case of animal altruism? Or just normal bonds of motherhood?
But this is a first for this observer.
What do you think will happen?
Stay tuned for updates in the coming weeks.