This photo available under a Creative Commons license shows a hooded pitohui (Pitohui dichrous) YUS Conservation area on the Huon Peninsula, Morobe Province, Papua New Guinea. They are among the most well-known examples of a toxic birds. (Courtesy Photo / Wikimedia)

This photo available under a Creative Commons license shows a hooded pitohui (Pitohui dichrous) YUS Conservation area on the Huon Peninsula, Morobe Province, Papua New Guinea. They are among the most well-known examples of a toxic birds. (Courtesy Photo / Wikimedia)

On the Trails: Toxic birds and bugs

These chemical compounds are often derived from plants

By Mary F. Willson

For the Juneau Empire

Thousands of insect species have chemical protection against predators or parasites. These chemical compounds are often derived from plants (which made them for their own defense); for instance, herbivorous larvae sequester these compounds, so they and the ensuing adults are protected. Enemies may be deterred from attack by the smell or learn from experience to avoid insects that produce nausea or other unpleasant effects. Chemical protection provides clear advantages to survival and reproduction. A well-known example is provided by monarch butterflies: The larvae eat milkweed plants, taking in toxic cardiac glycosides; birds that try to eat the larvae (or the later adults) get sick and quickly learn to avoid such prey.

A less well-known and fascinating example is the colorful bella or rattlebox moth, whose larvae feed on poisonous seeds of a legume, storing the toxic alkaloids in their bodies. Predatory orb-weaving spiders and wolf spiders reject toxin-laden larvae and adults. Female moths transmit the toxins to their eggs. Male moths transmit the toxins along with sperm during copulation, and females mate many times, building up their supplies of the toxins. Thus, the females and their offspring gain better defenses. Males advertise their supply of the toxins (with an airborne pheromone) and females favor males with bigger protective chemical gifts to offer, somehow even giving precedence to their sperm over those of others.

This photo available under a Creative Commons license shows a day flying Bella moth (Utetheisa ornatrix) seeks shelter on a rattlebox blossom (Crotalaria sp.) during a brief sun shower at Juno Dunes Natural Area. Pyrrolizidine alkaloids in the Crotalaria plants and seeds end up in the larva and adult Bella moth, offering them some protection from predators. (Courtesy Photo / Wikimedia)

This photo available under a Creative Commons license shows a day flying Bella moth (Utetheisa ornatrix) seeks shelter on a rattlebox blossom (Crotalaria sp.) during a brief sun shower at Juno Dunes Natural Area. Pyrrolizidine alkaloids in the Crotalaria plants and seeds end up in the larva and adult Bella moth, offering them some protection from predators. (Courtesy Photo / Wikimedia)

In contrast to the insects, very few birds are known to be toxic (at least to humans or other mammals). The European common quail (a subspecies of a widespread species) sometimes makes some human consumers ill, but only in fall when the birds are migrating south, possibly because of some seasonal food in the diet; other subspecies living in other regions are not usually considered to be toxic.

Bronze-wing pigeons in Australia attracted notice when introduced mammals (cats, foxes) died after eating them. The pigeons eat seeds, including those of a particular legume that contains toxins. I found no reports, however, of effects of pigeon-eating on native Australian animals (did they not eat pigeons, or were there no observations, or did they tolerate the toxins?).

The largely herbivorous spur-wing goose of Africa sometimes has poison in its body, perhaps from eating blister beetles, which contain the potent toxins cantharidin. These birds could be self-medicating by occasional beetle-eating, perhaps reducing intestinal worms and microbes. A contrast is seen with the great bustard of Eurasia, which is thought to self-medicate in this way, at least in some populations, although this bird is not reported to have toxic effects. As an interesting aside: In the mating season, male bustards eat more beetles than females, perhaps cleaning out their guts to demonstrate to females (which inspect the males’ rear ends) no diarrhea and a clean bill of health.

North American ruffed grouse sometimes made human consumers sick, but effects varied among individuals and were chiefly restricted to later winter and the eastern part of the North America in the 1800s and 1900s. These effects may have been due to winter diets that included mountain laurel, a species known to be toxic to sheep and whose honey is toxic to many consumers, even bees.

A small songbird called the red warbler, living in parts of Mexico, was long-ago reported to be unpalatable to humans; more recently certain toxic alkaloids have been identified from the feathers.

In all of these cases, the toxic effects are regional, seasonal or variable among consumers. It seems unlikely that the responsible compounds evolved because of their occasional effects on the particular consumers/predators; they might have some metabolic function, for example. In short, these toxic effects maybe incidental, from the point of view of the bird—they may not have evolved because of a protective function, in contrast to insects, and they may have some other function that provided an advantage that led to their evolution.

There are, however, a few known instances of direct deterrence or protection by avian toxins. Hoopoes in the Old World produce very smelly material from the uropygial (“preen”) gland near the tail. Females spread this stuff over their feathers and their chicks, and the chicks produce it too. It is said to contain certain bacteria that destroy other bacteria that would damage the feathers.

The best-known cases of toxic birds are some species of pitohui and the ifrita of New Guinea. Touching these birds’ feathers and skin leads to tingling and numbing in humans (a fact well-known to the local natives), so eventually researchers discovered that the feathers are coated with material that contains alkaloids called batrachotoxins — highly potent poisons similar to those of the famous poison-arrow frogs. These birds may get the toxins from eating certain beetles, probably storing them in the skin and spreading them while preening the feathers; the toxins are also found in muscle tissues. There is evidence that the toxins reduce populations of ectoparasites such as lice and ticks, as well as various predators such as snakes, raptors, arboreal marsupial mammals, and humans. Levels of the toxins vary among species and among regions.

The subject of avian toxins is little-studied, so far. Many other birds are reported to be unpalatable or noxious in one way or another, and it seems likely that careful research may turn up more cases of both incidental and evolved chemical protection.

• Mary F. Willson is a retired professor of ecology. “On the Trails” appears every Wednesday in the Juneau Empire.

More in News

Jasmine Chavez, a crew member aboard the Quantum of the Seas cruise ship, waves to her family during a cell phone conversation after disembarking from the ship at Marine Park on May 10. (Mark Sabbatini / Juneau Empire file photo)
Ships in port for the week of May 18

Here’s what to expect this week.

Juneau high school seniors Edward Hu of Juneau-Douglas High School: Yadaa.at Kalé (left), Elizabeth Djajalie of Thunder Mountain High School (center) and Kenyon Jordan of Yaaḵoosgé Daakahídi Alternative High School. (Photos of Hu and Jordan by Juneau Empire staff, photo of Djajalie by Victor Djajalie)
Senior Spotlight 2024: Three top students take very different paths to graduation stage

Ceremonies for Juneau’s three high schools take place Sunday.

The entrance road to Bartlett Regional Hospital. (Peter Segall / Juneau Empire file photo)
Bartlett Regional Hospital looking at eliminating or trimming six ‘non-core’ programs to stabilize finances

Rainforest Recovery Center, autism therapy, crisis stabilization, hospice among programs targeted.

A king salmon. (Ryan Hagerty/U.S. Fish and Wildlife Service)
Biden administration advances bid to list Gulf of Alaska king salmon as endangered or threatened

Experts say request could restrict activity affecting river habitats such as road, home construction

Mayor Beth Weldon (left), Deputy Mayor Michelle Bonnet Hale and Juneau Assembly member Paul Kelly discussion proposals for next year’s mill rate during an Assembly Finance Committee meeting on Wednesday night. (Mark Sabbatini / Juneau Empire)
Assembly members support lower 10.04 mill rate ahead of final vote on next year’s CBJ budget

Initial proposal called for raising current rate of 10.16 mills to 10.32 mills.

Dave Scanlan, general manager of Eaglecrest Ski Area, speaks to the City and Borough of Juneau Assembly Finance Committee on April 13, 2023. (Clarise Larson / Juneau Empire file photo)
Dave Scanlan forced out as Eaglecrest’s general manager, says decision ‘came as a complete shock to me’

Resort’s leader for past 7 years says board seeking a “more office-process, paper-oriented” manager.

The entrance to the Alaska Gasline Development Corp.’s Anchorage office is seen on Aug. 11, 2023. The state-owned AGDC is pushing for a massive project that would ship natural gas south from the North Slope, liquefy it and send it on tankers from Cook Inlet to Asian markets. The AGDC proposal is among many that have been raised since the 1970s to try commercialize the North Slope’s stranded natural gas. (Yereth Rosen/Alaska Beacon)
Eight young Alaskans sue to block proposed trans-Alaska natural gas pipeline

Plaintiffs cite climate change that harms their access to fish, wildlife and natural resources.

(Michael Penn / Juneau Empire file photo)
Police calls for Tuesday, May 21, 2024

This report contains public information from law enforcement and public safety agencies.

Most Read