Mainers used to love to go on about how short the summers were here.

Not any more.

Climate change has elongated summer through both an earlier spring onset and later fall continuation of warm temperatures. Some birds have been able to track those changes: Resident species start nesting earlier. A number of migrants arrive earlier and nest earlier, though that doesn’t always mean that their food supplies peak at the optimal time for feeding their hungry young.

One of the interesting ways that some birds seem to be adapting to warmer temperatures extending into the fall is by nesting later in the year. There were probably always some individual nesting pairs of birds that had bad luck in any particular year and lost their eggs or young to predators or bad weather. If that happens to a pair early enough in the season, then even a species that only raises a single brood per year will often try to renest. If the summer is short, that can mean that the young birds don’t mature fast enough to escape the ravages of cold weather and lack of food.

Another limiting factor for the length of the nesting season is that in most birds, the adults depart on their fall migration before their young, leaving their offspring to search for food and find their way south based on their instincts. The departure time of the adults may not push back in time that much even if the weather stays warm.

We’ve been seeing two families of recently fledged birds in our yard in September. One is a set of sibling young northern cardinals that noisily beg for food all day. A song sparrow family is doing the same. Both are species that are known to be able to nest at least three times in a season if the weather allows it. These are two species that have very large ranges across North America and are very abundant. Having that many broods per year is one of the reasons why they are so successful. In the case of the cardinal, it is also what fuels their continued northward expansion.

In addition, we’ve recently spotted groups of wild turkeys that include half-grown youngsters. At this time of year, we would have expected most turkeys to have attained full size or close to it. Wild turkeys are different from cardinals and song sparrows in that they only raise a single brood per year. However, if they lose their eggs, they can nest again. In the past, they probably would not attempt such a renest very late in the summer—young birds hatched too late would not be able to find enough food to mature before cold weather would have arrived. But now, these late broods appear to be doing ok, allowing more birds to be produced and survive. This is likely a major reason why some people find their yards are overrun by turkeys!

While down in Pemaquid Harbor recently, we were surprised to see two young ospreys still hanging around the nest just off the boat ramp there. They were fully capable of flying but were making the screechy calls that young ospreys make to urge their parents to bring food. While we were there, we didn’t see any sign of the adults, making us wonder if they might have already left to head south. While these young ospreys were capable flyers, we wondered if they had learned to fish or would get hungry enough to learn quickly. For them, the warm temperatures into September make it less energetically difficult for them; still, if they can’t figure out how to find food (or if the seasonal fish that they eat have moved on), they may not make it to become part of the osprey population and come back next year.

Clearly, the impacts of the changing climate on breeding birds are complex and vary greatly across species. Have you noticed birds nesting later this year too?

Jeffrey V. Wells, Ph.D., is a Fellow of the Cornell Lab of Ornithology and Vice President of Boreal Conservation for National Audubon. Dr. Wells is one of the nation's leading bird experts and conservation biologists. He is a coauthor of the seminal “Birds of Maine” book and author of the “Birder’s Conservation Handbook.” His grandfather, the late John Chase, was a columnist for the Boothbay Register for many years. Allison Childs Wells, formerly of the Cornell Lab of Ornithology, is a senior director at the Natural Resources Council of Maine, a nonprofit membership organization working statewide to protect the nature of Maine. Both are widely published natural history writers and are the authors of the popular books, “Maine’s Favorite Birds” (Down East Books) and “Birds of Aruba, Bonaire, and Curaçao: A Site and Field Guide,” (Cornell University Press).