Jay at al,
My assumption for the situation you describe would be diving ducks are absent because some of their staples, predominately animal items like crayfish, snails and small fish (like gizzard shad), are not present in sufficient/historical amounts. Of course, the
animals diving ducks feed on depend on bottom of the food chain things like plants, especially the "pond weeds" in the genus
Potamogeton. As for dabbling ducks, they eat mostly plant material. If both diving and dabbling ducks/geese are absent, this may indicate an issue that killed plant life (probably not permanently but maybe for one growing season). That issue could
be anything from water level, water temperature or a pollutant. I do not think the issue is the apartment construction in terms of noise/commotion. If the construction did something to interfere with inflow, pollute inflow, that might be a different matter.
The blackbirds depend on the cattails around the edge of the lake. Cattails are notorious for being pretty tolerant of conditions other water-loving plants can't handle. Don't put me on the stand, but these would be my thoughts.
For what it's worth, Windsor Lake has far fewer diving waterfowl this autumn than normal, and I have assumed rather than things just being late, the issue is a lack of schooling food fish (i.e., shad). In the world of CO water birds, "money" is shad and crayfish.
Follow the money by finding the gulls. Where the thieving gulls are is where the diving ducks/grebes/loons are, largely because that's where the shad/crayfish are.
Dave Leatherman
Fort Collins