Pine Siskin

Pine Siskins are a classic “irruptive” northern finch, meaning that their abundance each year – especially south of the breeding range – varies extensively in response to food supplies. Despite their name, the main drivers of siskin movements are probably spruce and birch seed crops, which are common plants in their northern breeding range. When these crops are poor, siskins are more likely to depart, and travel further, in search of a more reliable food supply. In winter in New England, they are frequently seen in pines and weedy fields in addition to spruce and birch and are well-known consumers of sunflower and nyger (aka “thistle”) seeds at feeders.

Typically, siskins move south in numbers every other year, although as the trend graph indicates there is a lot of variation here. Birds show limited faithfulness to either breeding or wintering locations, and recaptures of banded birds have revealed some extreme cases of this nomadism. For example, a siskin banded in Quebec one winter was relocated in California in a subsequent one: a distance of almost 4000 miles. In years with especially abundant food in the wintering area, a few siskins may remain to breed the following spring. They are early nesters and can begin courtship in January and build nests in February and March. Because the incubation and nestling periods take up roughly a month, these early nesting siskins will often have fledged young and departed for parts unknown before many other migrants have returned to New Hampshire.

On the siskin trend graph there is an interesting difference between data for the breeding (BBS) and winter (CBC) seasons. While the high variation between years is to be expected for a species such as this, it’s harder to explain why siskins were most common as breeders during a period when they were relatively rare in the winter (~1995-2001). More disconcerting is their extreme rarity on the BBS after this period (e.g., compared to before 1995), while their winter pattern returned to peaks every 2-3 years. Pine Siskins are but one of several northern species showing shifts in population trends around the year 2000, and these bear further investigation to determine if there are unknown threats affecting boreal forests and their birds.