Posted by: Ann McKellar
American redstarts (Setophaga ruticilla) are long-distance migratory warblers that typically begin arriving in the Opinicon region in early May. A female will pair with a male, inspect their shared territory, and then build a nest over several days. But as the breeding season progresses and nests continue to be depredated, a female can typically build new nests more quickly, sometimes managing to build an entire nest in as little as a day in late June and July. Redstart nests are usually built at the junction of three branches (also known as a crotch), often on the main trunk of a small tree or on skinnier branches of a larger tree. This type of structure allows support for the small cup nest, and a female will often be found placing her breast in various crotches before deciding where to build. When nest-building, female redstarts begin by laying down a base of spider web, and subsequently attach various materials, which can include bark strips, grasses, leaves, and lichens, to build up the walls of the nest. The final stage involves lining the inside of the cup, which is often done with feathers and mammal hairs.
On June 30, 2010, I observed a female American redstart laying down spider web in a crotch of a small sugar maple near Rock Lake
Lane. I returned the next day, expecting to find the nest well on its way to completion. Instead, I found that the previous day’s nesting attempt had been abandoned, although the female still appeared to be building a nest somewhere nearby, as I saw her carrying nesting material. Puzzled, I continued to search for the female’s new nest for the next few days, without any luck. Finally, on July 6, I found the same female incubating three eggs in what appeared to be an old red-eyed vireo’s (Vireo olivaceus) nest. Red-eyed vireos construct their nests suspended from a fork or from two lateral twigs, and they are very different in appearance from the smaller, more secure-looking redstart nests. I was very surprised by this discovery, but after some research, I found that the use of old or deserted nests of other species, although not common, has been described previously in American redstarts. Verdi Burtch (1898) reported an American redstart female using an old red-eyed vireo’s nest that she had freshly lined, and Alfred Otto Gross noted in Bent (1953) three cases in which a red-eyed vireo’s nest was used by an American redstart female, one in which a yellow-throated vireo’s (Vireo flavifrons) nest was used, and one in which a nest started and abandoned by a yellow warbler (Dendroica petechia) was used.
The redstart-vireo nest was ultimately depredated four days later, perhaps partly due to its conspicuousness. At this point I collected the nest in order to observe it more closely. The redstart had indeed used the foundation of a hanging red-eyed vireo nest, but had added some of her own lining material, which explains why I saw her with material on July 1. I suspect that the she was becoming desperate at such a late stage of the breeding season (two of her previous nests had already been depredated) and, giving up on starting a third nest from scratch, she decided to quickly re-line the already-constructed vireo nest.
- Bent, A.C. 1953. Life histories of North American wood warblers. Dover Publishers: New York, New York, USA.
- Burtch, V. 1898. Curious nesting of the American redstart. Auk 15: 332.