I agree 100% I shot a mallard in a cornfield one time and when I went to pick it up, it was literally crawling with freshwater shrimp.
yup, and those tiny sticky eggs from perch, minnows, sticklebacks, and other shallow water spawning fish stick in their feathers as they swim thru the moss & weeds. No reason to think zebra mussel larva wouldnt hitch a ride. every single slough, pothole, livestock watering pond, and gravel pit out there has all those fish and more in them, and its not from game & fish stocking.
It'd be interesting to shoot a few ducks & geese and dunk them in an aquarium full of clean water just to see whats hitching rides. I've looked al over the internet for a similar experiment but can't find anything...surely I'm not the only one thats thought of doing this.
There was an experiment they did, in europe I think, where they fed ducks fertile fish eggs, and a small percentage of the eggs got pooped out undamaged with wiggling embryos in them, but I still say sticking to feathers is the primary way of transport.
I did find one study where they found .2 zebra mussel veligers per duck. seems insignifigant, but I bet with different bird species that have different swimming habits in different water bodies at different times of the year, that number can be significantly higher.