There's a New Bird in Town: Irruptions and Superflights

Is there a new species of bird at your feeder? One that you have never seen or haven't seen for a long time? Every few years we have what are known as "irruption" years. These are years when finches and other species that generally winter in the boreal forest in Canada and the far north, move south to the joy and amazement of bird enthusiasts. These travelers include members of the finch family such as pine siskins, evening grosbeaks and redpolls as well as "honorary" finches like the red-breasted nuthatch. The birds are responding to a poor production of cones and seeds over the summer foreshadowing tough times over winter when these seeds are the primary food source the finches depend on. An irruption occurs when large numbers of birds move beyond their typical range, usually in response to low food supplies.

Why do irruptions occur?

The short answer is they occur because of a lack of food but predicting which bird species will move is more complicated. Most of the finch species that winter in the boreal forests of Canada and Alaska depend on seeds or hard mast produced by conifers such as pines, spruce, and hemlock as well as the seeds produced by deciduous trees such as maple, birch, and beech. Each type of bird has a preferred diet and some specialize primarily on one or a few species of trees while others feed on many. The trees have their own tricks to try and ensure that all their seeds are not taken. Some years they have bumper crops where there are more than enough seeds for all the "seed predators" and will be plenty left over to grow into new trees. Other years there are very few seeds so the "seed predators" have to leave or switch to a different food source. This helps to keep the "seed predator" numbers below what could be supported if the trees produced at the same rate each year.

Weather conditions such as drought can also influence the seed crop. To complicate matters, tree species are not necessarily synchronized with each other. Each tree species has its own pattern of seed production boom and bust cycles. Just because there are few white pine cones does not necessarily mean there are no hemlock seeds. Irruptions occur when seed or cone production is low across a wide geographic area forcing the birds that depend on them to move in search of food. When multiple types of trees fail to produce a seed crop during the same year, you can expect multiple species of birds to pack their bags and move south. The larger the geographic area of the seed failure and the more tree species involved, the larger the number of species and individuals of birds moving out of their typical winter range. When this occurs, we have what is called a "superflight", multiple species of finches irrupting at the same time.

How often do irruptions and superflights occur?

Every couple of years, we may have 1 or 2 species moving south out of their normal range but it is much less common to have a year with a superflight with 6 or more species moving south into the central and southern US.­ Previous superflights occurred the winters of 1968-69, 1982-83, 1997-98 and 2012-13. Scientists track the cone crops to make predictions on when irruptions may occur and when we might see a superflight. The winter of 2020-2021 is predicted to be a superflight year, and widespread reporting from bird watchers across the country confirm massive influxes of multiple species including pine siskins, evening grosbeaks, purple finches and red-breasted nuthatches as far south as the central and southern US.

Where can I find irruptive finches?

As with most species of birds, these birds are searching for the food they are familiar with. Search for them in areas with conifers such as pines, hemlocks and spruces particularly where the seed crop is good and there are many cones. For example, white-winged crossbills specialize on extracting seeds from spruce cones and have been reported at ornamental stands of spruce in backyards, cemeteries, and public open spaces. Species such as the common redpoll that feed on deciduous catkins and seeds will often be found feeding in birches, aspens, and maples. Pine grosbeaks feed heavily on fruit so are attracted to areas with an abundant fruit source produced by trees like mountain ash, hawthorn, and crabapple. As a long term strategy, including some of these tree species in your backyard landscaping plan will increase your chances of attracting these nomads. See Landscaping for Wildlife and Shrubs and Trees for the Winter Landscape for more information. All of these species will also frequent bird feeders which is where the fun really begins. Stock your feeder with nyjer and finch mixes for the smaller species like redpolls and pine siskins, evening grosbeaks prefer striped sunflower seeds and just about all of them will visit platform feeders with black-oil sunflower seeds. For more on winter bird feeding see Winter Bird Feeding:The Basics.

Which species of birds are irruptive finches?

Check out your favorite field guide or online source for more information on how to identify the different species. The species listed below are ones that typically show irruptive behavior.

Family Fringillidae – The finch Family

Evening grosbeak – Coccothraustes vespertinus – The evening grosbeak is the king of the irruptive finches. With its bold yellow, black and white pattern and a bill that makes a cardinal look delicate, they are the jewel in the crown and a special species to have in yards and at feeders. When they arrive at your feeder, you will know it, and you should be prepared to provide lots of sunflower seeds to keep these demanding guests happy. They prefer the large striped sunflower seeds which they crush with their massive conical bill, but smaller black oil sunflower seeds will also be taken.

Pine grosbeak – Pinicola enucleator – Pine grosbeaks are large, chunky finches with a short, stubby, conical bill.  The males are gray and red while the females have yellow highlights. These birds feed on mountain ash fruit and seeds as well as the buds, seeds and fruit of spruce, pines, and crabapple. At feeders, they will come to black oil sunflower seeds as well as suet and fruit.

Purple finch – Haemorhous purpureus – These finches look very similar to the more common house finch H. mexicanus  but can be distinguished by their color and streaking patterns. The male is a rich raspberry red. Female purple finches are brown with streaks and have a broad white eye stripe.  Purple finches breed across Canada and into the NE United States. In winter, they wander across central and southeastern US in search of an ample winter food supply. At feeders, purple finches will be attracted to black oil sunflower seeds, nyjer, and millet. 

Red and white-winged crossbill – Loxia curvirostra and L. leucopter – The crossbills are two of the most unusual of the irruptive finches and examples of the extremes in specialization that occur in some birds. Crossbills, as the name suggests, have a crossed bill that is perfect for extracting seeds from conifer cones. They are the most efficient of all the boreal forest finches at extracting seeds from tightly closed conifer cones, but the specialization comes with a cost. They are much less efficient at feeding on other seeds.  During years with a poor cone crop, the crossbills move in search of other food sources, but they are less good competitors than other finch species and often suffer high rates of mortality when conifer crops fail over large areas.

Common and hoary redpoll – Acanthis flammea and A. hornemanni   Redpolls are similar to pine siskins and goldfinches in size, shape, and behavior. Redpolls are small seed-eating finches with a red patch on the top of their head. They travel in flocks feeding on seeds of trees such as birch, alder and willow as well as in weedy fields. They are often seen mixed in with other finches and are a special treat as visitors to a backyard feeding station. At feeders, they prefer smaller seeds such as nyjer and millet. 

Pine siskin – Spinus pinus – Pine siskins are one of the most common of the boreal finches to move into the central and southern US. They tend to travel in large flocks and are present some years in large numbers and absent the next. The pine siskin is a small streaked finch with patches of yellow in its wings. Its tiny bill is adapted to feeding on small seeds. Pine siskins are often seen at feeders where they may be found in large flocks mixed in with American goldfinches and house finches. Their favorite food at feeders include nyjer seed and black-oil sunflower seeds.

Family Sittidae – The nuthatch Family

Red-breasted nuthatch – Sitta canadensis – The red-breasted nuthatch is the smaller cousin of our more common and familiar white-breasted nuthatch S. carolinensis It is smaller and more delicate, has a black line through the eye with a white line above and a reddish breast. Nuthatches frequently feed on the bark of the tree distinguishing themselves by walking down the trunk of the tree. While white-breasted nuthatches are associated primarily with deciduous forests, the red-breasted nuthatch makes its home in coniferous or mixed forests. The red-breasted nuthatch is considered an "honorary finch" because it shows similar irruptive patterns of movement to those of the boreal finches is response to food shortage. Red-breasted nuthatches show irruptive movements every 2-3 years and at bird-feeders are attracted to black-oil sunflower seeds, peanuts, and suet. 

For more information

Winter finch Forecast – The winter finch forecast from the Finch Research Network occurs annually in early fall and gives a prediction on whether boreal finches will be flocking south and which species will be moving based on the cone and seed crops of multiple tree species across Canada.  It is highly anticipated by bird watchers each fall.

Facebook page "Finches, Irruptions, and Mast Crops" – Many local, regional and national bird groups and clubs host Facebook pages which are great places to find out what types of birds have been reported in your area. There is one page specifically devoted to these irruptions called "Finches, Irruptions, and Mast Crops". It is a public group to share pictures and information on finches, irruptions and mast crops.

Ebird – The explore feature in Cornell Lab's eBird allows you to search by species or location to see what birds have been found in your area.