Pine Siskins are known as irruptive “winter finches.” What does this mean?
Flock migration is highly variable from year to year. The are irruptive because large numbers may move south in some years and hardly any in others. This is based on the success of crops from year to year.
These small birds are extremely hardy and can survive in very cold temperatures. High metabolic rates and the ability to store up to 10% of their body weight in seeds in their crop overnight to provide extra food on cold days give this species a survival advantage when winter temperatures take a plunge.
A group of pine siskin is known as a “charm,” “company,” and a “trembling.”