Consider the topic areas below simplistic. Species of different stripes tend to be scattered all over the chart when it comes to characteristics and shun sweeping generalizations. Still, at the risk of sounding overly broad, it's instructive to address some common tendencies.
Apart from the few species which tend to be found in flocks nearly all year (think European starlings, Franklin's gulls, or cedar waxwings), most birds tend to spend periods alone or in family groups, at least during the breeding season. Once nesting becomes a memory, however, the tendency is for birds to gather, often with dissimilar species. In fact, given the relative brevity of the breeding season, flocking or grouping would have to be considered the more normal state among many species.
Of course birds are not alone in their tendency to group up. Many parallels exist in the animal kingdom such as shoaling fish, the herding of large mammals, and certain swarming insects. No one is entirely certain why this grouping behavior, but it does bring some advantages to the individual as well as the flock. More eyes are alert for predators, food sources are found with more efficiency and, in the case of some species, even heat preservation is a factor.
If you get a chance to see a flock of mallards this week take a good look at them. It should be immediately apparent the birds no longer appear as they did earlier in the year. In fall some birds take on a look so different from spring, you'd think they were not even the same species.
Feather molt and feather wear are integral to a bird's appearance. The tendency is for birds of the northern hemisphere to appear in their best feather condition at or near the breeding season. Apart from this brief period, species take on myriad molt strategies to replace worn and weathered feathers, which tend to change the overall appearance of birds, some quite dramatically.
Pay particular attention to the few warbler species which are still trickling south. Chestnut-sided warblers, for instance, seem so changed from two months ago one would think they were looking at a completely different bird.
Jogging through Elmwood Park last week I was struck by the near absence of birdsong. Just weeks ago a person walking along those wooded paths would have been inundated by a multi-species chorus of singing, nearly throughout the day. Not so anymore.
Of the few birds still being heard, there is a curious tendency for songs to be quite different than those heard in spring. Within just the past week I've listened to western meadowlarks, marsh wrens and eastern wood-pewees singing. All sound like half-hearted attempts at the real thing, like listening to the orchestra warm up prior to the concert.
I'm not sure exactly who is doing the singing, whether it's young birds testing their vocal abilities for the first time or adults with diminished hormones, but there is a starkly discernable difference in quality from that of their spring songs.
We have a tendency to associate singing with nesting behavior. But as a biologist friend reminded me, communication among individuals is still taking place despite the breeding season being over. That's undoubtedly true but the quality of this communication is certainly diminished, at least to the human ear.
Whooping cranes migrate twice every year between nesting grounds in northern Canada and their wintering area along the gulf coast of Texas. Seeing one of these large rare birds is a treat, particularly here in North Dakota where the birds are spotted briefly during each migratory movement.
If checking whooping crane off your North Dakota birds list is a goal, you might want to put more emphasis on the fall season. Why? Birds tend to linger this time of year.
The spring migration of birds tends to be a hurried affair with individuals dashing north driven by stored energy and hormones in an effort to claim the best nesting territory. In fall, however, it seems a more calculated approach is taken. Other than to beat approaching bad weather or slowly diminishing food supplies, there really is no rush. Instead the birds tend to linger noticeably longer than spring.