Last week, as my son and I were doing some yard maintenance, and I was deliberating on from which bunch of hostas I should dig to provide a plant for a friend, I looked up to discover grasses emerging from the external vent to my dryer. I called over my son and he, since he had on his gardening gloves, carefully removed what we determined to be a small bird's nest from our vent. It can't have been there long and there were no eggs in it.
Lo and behold, our neighbour's dryer vent had one too! So, M removed the nest from theirs as well. The flapper had been lifted up to allow for access. Hopefully, they will find a new nesting site. One that doesn't involve house vents!
Word of advice, check your vents. It is mating season for the local birds but your vent is not a good nesting site. It can be a fire hazard to your home too if they nest in a dryer vent as these did.