Authored by Phil Doerr.
Watch for them along woodland edges and shrubby corridors in open fields! It’s July in North Carolina, the heat is building, the milkweed is flowering, thistles are setting seed and the not always patient American goldfinches are ready! Perhaps worried the male will botch the job, female goldfinches build the nest, using 2-3 vertical stems as a base about which she weaves small twigs and bark strips to fabricate a cup. She’ll then line the cup with small plant rootlets and downy materials from thistle seed or milkweed pods. The females collect the cottony down of thistle seeds and milkweed pods to cushion her eggs. She will collect thousands of these to weave into the cup of the nest. The entire project is stitched together with spider silk! And, the resulting cup is famous for being so tightly woven it will hold water. Careful scrutiny of the top down view of the nest illustrates her skill.
This construction may take an exhausting week of work, followed by several days of egg laying, to produce the customary 2-7 egg clutch. Sitting the eggs for 2 a week incubation, the female will take occasional feeding breaks, but is often fed by the male . Once the eggs hatch, the male will begin nearly nonstop seed deliveries for the female to pass to the demanding nestlings. Soon the demands escalate as the chicks grow, however, and both parents will feed. After nearly 2 weeks, the nestlings “fledge” (leave the nest) but continue to beg piteously. The male will feed them a few more days, but the female has more important business, now…. It’s been a month or more since she began building the first nest, and her best investment now is to initiate another brood quickly!
So now she will leave her fledglings with the doting dad to finish the job and often, as we mentioned last month, seeks out another spot to initiate a new nest with another male!
While this may at first seem a questionable behavior it does have ecological, and evolutionary benefits. First, there’s another 6 weeks of summer weather with an abundance of seedy delights and soft fluffy goodies for nest building, so plenty of time to fit another brood in!
Thus the female has a chance to double the number of offspring with her genes in the annual lottery and add the potential benefits of a second male. She’s a bet hedger! No point in putting your eggs in a single basket when options are available! Second, this strategy also helps to compensate for the unbalanced sex ratio among adults that favors males…it provides an opportunity for more males to breed than could otherwise. Females are often a scarce resource among American Goldfinch populations. There is some thought that females may be worn out by the fall, and grateful for a less demanding life style.
As always, remember the importance of the weedy edges, gardens and roadside fence vegetation in providing the seed crops American Goldfinches need to survive, and which provide habitat for all the invertebrates (insects, and various creepy crawlies) the other birds need! You can convert part of your lawn to native plants, and help all the wildlife!
Thanks for all you do for birds! It is the way!