by Stan Tekiela
July 21, 2006
Photo by Stan Tekiela©
Given a niche, Mother Nature will fill it. I see it time and time again during my travels to photograph nature. By the dog days of summer, most birds are finished nesting and raising their young for the year, however one species of bird is just getting underway—the American Goldfinch (Carduelis tristis).
A good rule of thumb is, song birds who feed their babies insects will nest early in the season while song birds that feed their babies seeds need to wait until later in the season when the seeds are ripe. That is why the majority of seed eating song birds raise their young with insects—except for the goldfinch.
The reason why song birds feed their young insects is because the baby’s digestive systems are not yet developed. Insects are easy to digest when compared to seeds. A good example of t his are Northern Cardinals. As adults they feed upon seeds but their babies are feed an insect diet. Slowly over time the parents will start to introduce seeds and other plant material to their baby’s diet as their digestive system develops. By the time they are on their own the babies are eating seeds exclusively. Not with the American Goldfinch.
An insect diet is high in protein and allows the young birds to grow quickly. Some species such as House Wrens grow so quickly that the babies are able to leave the nest and fly in just 12 days. The only problem is, they need a lot of insects to keep the babies fed so the parents act like conveyor belts with wings—constantly bringing more bugs. On average, adult birds that feed their young insects will bring a new mouthful of insects to the nestlings every 10- to 15 minutes. This means a lot of trips to the nest from sunrise to sunset. Now these are dedicated parents. American Goldfinch don’t do this.
American Goldfinch are a small yellow and black finch. Like most finch species they feed nearly exclusively on seeds and other plant materials and so do their chicks. Seeds are so important to the American Goldfinch that they will actually hold off on breeding until mid to late summer in order to time the hatching of their chicks with the ripening of the seed crop. In particular, the goldfinch is waiting for the thistle seeds to ripen.
There are many varieties of thistle. Most are two to three feet tall and tend to grown in open fields, along road sides, in ditches and in farmers fields. They usually have prickles or thorns and they often grow in large groups. In general they are not well liked by many people but the American Goldfinch loves them.
As we learned earlier, the American Goldfinch feed their young a seed diet exclusively. Both male and female goldfinch will feed their babies. Now here is the interesting part. After feeding upon the ripened seeds the adults will return to the nest and regurgitate a mass of partially digested seeds along with a milky liquid. Stick with me for a moment while I explain why this is interesting.
A bird’s digestive system has two stomachs. The first is called the gizzard and is used to grind up the food in a dry environment. Since birds don’t have teeth they need this front-line stomach for grinding their food. The problem is, no real digesting occurs in the gizzard, just breaking up of the food. Digestion usually takes part in the second stomach where the stomach acids are located. So when a goldfinch regurgitates up the seeds it is assumed it comes from the first and not the second stomach. So where does this liquid mass come from? It is not known
What is known is that American Goldfinch chicks grow extremely fast on the seed and liquid diet. What is more interesting is that the parents only feed their babies about once every 1 to 2 hours. Compare that to the insect feeding parents which are constantly stuffing their babies mouths with insects. Apparently the seeds and liquid diet is so nutritious the babies only need to be fed once an hour.
I would call the American Goldfinch a champion at filling a seed eating niche. How about you? Until next time…
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