Why am I seeing fewer birds in my area?
It's not unusual to find slight shifts in waterfowl populations as well as migration routes and timing from year to year.
It is quite normal for ducks and geese to congregate in the spring and fall, but summer nesting ducks are typically more solitary. When we see groups of adult waterfowl in the summer, they are birds that either couldn't find a mate or finished breeding early.
Following the food
Birds will always follow their food source, so that's one possible reason why you're not seeing as many. Change in water levels, water quality or the presence of introduced/invasive species might influence food availability. Alternatively, the birds may have, by chance, chosen to spend more time at another lake or wetland. For more information about birds in your area, you may be interested to explore the species accounts or your region on iNaturalist, which compiles data from local observations.
Is it normal to see a lone duck?
Please be reassured: it is not unusual for waterfowl to stick around longer than appears wise. In fact, mallards, which could very well be what you’re seeing, have the most prolonged migration of any duck species. It’s not unusual for them to stay in this region until late November.
As long as there is access to food and water, they can manage the cold temperatures. It's very likely the duck you're seeing will be just fine!