Swiftlets and ticks
Answers to readers' questions about bird's-nest soup and ectoparasites
Published: August 26, 2011
In your last column, you mentioned that the nest of a swiftlet in Asia is used to make bird’s-nest soup, a delicacy in Chinese cuisine. (See August 2011, page 10.) How does that affect the birds? — Alice Barnes, Golden, Colorado
The tiny, half-ounce nests of several species of Asian swiftlets are used to make bird’s-nest soup. The nest is a shallow cup that is attached to a wall, typically in caves. The male builds it over a period of about a month from salivary gland secretions.
The species known as the Edible-nest Swiftlet produces the most valuable nests, because they are composed nearly entirely of hardened strands of saliva. Other swiftlet species incorporate conifer needles, feathers, grasses, or plant material in their nests, and they require more labor to prepare for cooking, so they’re less desirable for soup.
The preparation involves rounds of soaking, cleaning, and shredding. Once foreign matter is eliminated, the material is then cooked into a gelatinous soup or stew, sometimes with sweeteners or other ingredients.
Swiftlet nests have been used as food in Asia for centuries. Throughout history, cultural traditions have generally assured sustainable harvesting. Nests are collected after the young have fledged, and to ensure that the swiftlets can continue to reproduce, not all nests are destroyed. Yet increased demand, particularly among the middle and upper classes in China, has led to exploitation in some areas over the last decade. And aside from depleting swiftlet numbers, the plundering of caves also threatens other cave organisms.
Fortunately, the swiftlets will use man-made structures instead of caves. House- or barn-like buildings are erected near natural colonies, or nests may be harvested from existing structures that are already occupied by swiftlets.
Swiftlet farming is becoming a lucrative business, since nests sell for about $1,000 a pound. Indonesia, Thailand, and Malaysia are the leading producers of farmed bird’s nests.
Farms presumably help take pressure off cave-dwelling populations. However, farming has increased the popularity of bird’s-nest soup, and harvesting from caves remains problematic in certain areas. I wonder if oversupply will eventually push prices down and make the soup a less appealing, pedestrian food item some day.
I saw an Eastern Wood-Pewee with at least a dozen ticks on its forehead. The bird did not act sick or injured. Can you shed light on this poor bird’s situation? — Margie Rutbell, New Hope, Pennsylvania
Birds are susceptible to many ectoparasites. Ticks are common and easily visible. Studies that I have read found the incidence of ticks on birds captured for banding at 4 to 15 percent.
In the eastern United States, the species that infests birds most commonly is the blacklegged tick or deer tick, Ixodes scapularis. It has multiple hosts. In addition to birds, mammals as small as mice and as large as deer are the primary hosts.
Twice during its life cycle, the blacklegged tick drops to the ground, either to molt or to overwinter. Therefore, birds that forage on the ground or in low vegetation are most susceptible to it (as well as to other tick species). Frequently reported victims are thrushes, including robins; sparrows (Chipping and Swamp are mentioned often); and ground-dwelling warblers such as Common Yellowthroat, Ovenbird, Worm-eating and Hooded Warblers, and Northern Waterthrush.
Your sighting of a pewee with ticks — especially so many ticks — is unusual, given the canopy-dwelling habits of the species. I have come across only one or two reports of ticks on flycatchers. The highest number of ticks on a single bird I’ve found, reported by a bander, is eight.
Ticks are usually on the heads of birds, as you noted, where they are inaccessible to preening bills. The insects typically are more of an inconvenience than a threat. If an engorged tick is near the eye, it could temporarily obstruct vision. Theoretically, multiple ticks could cause troublesome blood loss in a small bird, but I have not heard of them harming otherwise healthy individuals. Once ticks become engorged on blood (a process that takes several days), they fall off, and the bird usually recovers completely.