Back in November and December, when I was doing some scouting in my assigned Christmas Bird Count area, I was seeing groups of Cassin's finches on a regular basis in Granite Basin. Cassin's finches are an example of a bird species that has 'irruptive' years, where they migrate beyond their normal range.

Most migratory species exhibit a predictable pattern year after year, wintering in the same location with reliability and dependability. However, there are some migratory bird species such as finches, siskins and grosbeaks where their migration pattern is unpredictable from year to year.
Factors affecting their winter distribution usually are related either to weather conditions or food availability. Probably one of the best examples of irregular migration behavior is that of snowy owls. In a 'normal' year, they tend to stay farther north, when the weather is agreeable and food sources are plentiful.

However, when the weather at northern latitudes is extremely harsh, making it difficult to find food, or when there is a crash in their food supply, they will migrate much farther south compared to a 'normal' year. When this event occurs, it is referred to as an irruptive year.

This behavior is observed not only in birds of prey, but is also evident in song birds that typically eat seeds and nuts at either high latitude or high elevation locations. Drought conditions can affect the production of seeds and nuts, and if there is not a sufficient supply of food to sustain these species they will roam far and wide to find the food they need to survive.

The fact that Cassin's finches were occurring in the national forest several months ago was interesting, and I kept wondering if perhaps they would move into urban areas where there are feeders. For several months this didn't happen, and then all of a sudden it seemed after our last big storm system there was a movement in the population and they suddenly started showing up all over Prescott at backyard bird feeders.

This past week, I counted 18 Cassin's finches at my seed feeder at one time! I am not seeing as many now that the weather has cleared up, but it will be interesting to see how long they stick around before they move north for breeding.

Not familiar with Cassin's finches? Are you wondering if maybe they are at your feeders? It is very likely that you have had Cassin's finches in your yard and you didn't even realize it! To the casual observer, it may seem that you are seeing a lot of house finches in your yard. However, upon closer examination, you will see the differences in plumage between the two species.

Cassin's finches are similar in appearance to our abundant, year-round house finches. Males in both species have red on the head and breast, and females are generally brown overall with streaking and lack any red.

Cassin's finches are slightly larger than house finches, the red in the males is more vibrant and intense and the streaking on the females is more defined and crisp. Another difference is the fact that Cassin's finches appear to have a bit of a 'crest,' whereas house finches lack this feature.

This Saturday, March 14, at 8:30 a.m., the Prescott Audubon Society will be leading a free guided bird walk at the Highlands Center for Natural History, 1375 S. Walker Road. The bird walk is open to everyone regardless of skill level. There is a good chance you might see some Cassin's finches on this bird walk!

Until next week, Happy Birding!