(Beyond Pesticides, August 27, 2018) Beyond the visual and audial charms of some bird species, insect-eating birds play a significant role in controlling pests that can ruin crops or ravage forests. A meta-study by Martin Nyffeler, Ph.D. of the University of Basel in Switzerland finds that globally, birds annually consume 400-plus million metric tons of various insects, including moths, aphids, beetles, grasshoppers, crickets, and other arthropods (invertebrate organisms with exoskeletons, paired and jointed appendages, and segmented bodies, such as insects, crustaceans, and spiders). This research reviews 103 studies that examine the volume of insects consumed by various birds in seven of the world’s major biomes.
In consuming such volumes of insects that can inflict damage on crops, trees, and other plants on which organisms may feed or otherwise depend, birds provide significant services to ecosystems, to denizens of habitats, and to human food system and economic interests; they also keep local ecosystems in balance. Threats to birds — and thus, to those ecosystem services — include those from pesticide use.
Of the 10,700 known bird species distributed across the planet, more than 6,000 are primarily insectivorous. The study indicates that forest-dwelling birds consume the majority of insects (approximately 300 million metric tons), and the balance (100 million metric tons) is devoured by birds living in crop- and grasslands, savannas, deserts, and Arctic tundra. Birds are especially interested in insects during breeding seasons, when they seek protein-rich food for their hatchlings.
Dr. Nyffeler comments, “The estimates presented in this paper emphasize the ecological and economic importance of insectivorous birds in suppressing potentially harmful insect pests on a global scale — especially in forested areas,” noting that this is especially so for tropical, temperate, and boreal forest ecosystems. He adds, “Only a few other predator groups such as spiders and entomophagous insects (including in particular predacious ants) can keep up with the insectivorous birds in their capacity to suppress plant-eating insect populations on a global scale.” In a previous study, he found that spiders eat 400–800 million tons of insects each year.
Birds’ role in protecting vulnerable and valuable plant life, as well as other features of ecosystems, deserves greater understanding and appreciation. Given that birds themselves are vulnerable to a multitude of threats, such understanding is urgent. As Dr. Nyffeler notes, “Birds are an endangered class of animals because they are heavily threatened by factors such as afforestation, intensification of agriculture, spread of systemic pesticides, predation by domestic cats, collisions with man-made structures, light pollution and climate change. If these global threats cannot soon be resolved, we must fear that the vital ecosystem services that birds provide — such as the suppression of insect pests — will be lost.”
Rachel Carson began to warn us, in 1962, that pesticides were a distinct threat to bird populations. She famously wrote, in her groundbreaking book, Silent Spring, that pesticides were causing “the sudden silencing of the song of birds.” A litany of bird die-off events is only the anecdotal tip of the iceberg. Indeed, the Defenders of Wildlife white paper report, The Dangers of Pesticides to Wildlife, notes that, “Some scientists have likened bird deaths from pesticides to an iceberg: those that are actually found and analyzed and whose deaths can be attributed represent the tip of the iceberg. The base of the pyramid represents the majority of pesticide related bird deaths that go undetected.” Just two of those were: a 2014 mass die-off of 700 birds in New South Wales, Australia from use of the pesticide fenthion, which was implicated in a number of bird kills in the Florida, California, Louisiana, and Massachusetts; and in 2016 in Maryland, the deaths of 13 bald eagles after they ingested the highly toxic pesticide, carbofuran.
Pesticides threaten birds through a number of vectors: direct ingestion of pesticide granules that birds pick up while searching for seeds, consumption of insects that have been killed by pesticides, and ingestion of pesticide-treated seeds, among other routes. The nature of the impacts on birds is likewise varied, depending on the particular pesticide’s toxicity, its persistence in the environment, amounts of pesticide applied, any synergy with other pesticides present, delivery method and location, general ecosystem impacts, and whether the particular compound concentrates through the food chain. Effects of pesticides on birds include: starvation; endocrine disruption and dysfunction; nervous system toxicity; and behavioral changes that imperil survival and/or successful reproduction.
Bird populations are in decline in the U.S. (especially among grassland species). A 2013 study found that the best predictor of bird declines is the risk from pesticide use, to which birds are especially vulnerable. Neonicotinoid pesticides (neonics) appear to be a particular culprit in birds’ slumping numbers. The American Bird Conservancy issued a report in 2013, titled The Impact of the Nation’s Most Widely Used Insecticides on Birds, that sets out the risks to birds of neonicotinoids, the most-common toxic pesticides in use in the U.S.
A Defenders of Wildlife report notes, “Many experts believe birds are amongst the most vulnerable species when it comes to pesticide exposure and serve as sentinels of the quality of the environment. One reason they are most susceptible is that they are very mobile and difficult to exclude from areas that have been treated with pesticides and there is little that can be done to prevent them from landing in areas that have recently been treated. Their susceptibility relates to their high rates of ventilation and inhalation of vapor and fine droplets, which makes them at risk from pesticides that are sprayed. They also ingest pesticides through their food and by preening and grooming and by absorbing them through their skin and their feet.”
Bird populations are affected by pesticides indirectly, as well as directly. A 2014 Dutch study linked the use of a neonicotinoid pesticide — imidacloprid — to reductions in localized bird populations; the mechanism was the significant reduction of populations of the insects on which they feed, such as beetles, mosquitoes, moths, aphids, and others. Pushback from industry on that study’s results were contravened by a report from the Task Force on Systemic Pesticides, which analyzed the findings of more than 800 peer-reviewed publications on the impacts of systemic pesticides: “The report emphasizes that neonicotinoids and their metabolites are persistent and harmful, even at very low levels, and that the chemicals have far-reaching impacts on entire ecosystems, from direct exposure to persistence in soil and water. Bees, butterflies, worms, and other pollinators and non-target organisms are also put at risk. Scientists concluded that even when neonicotinoids were used according to guidelines on their labels, the chemicals’ levels in the environment still frequently exceeded the lowest levels known to be harmful to a wide range of species.”
In the summer of 2018, new research pointed to an alarming ubiquity of neonicotinoids once released into the environment. The study, by a group from the University of Guelph, Ontario points to the wide effects of neonics on wildlife. The team found that 25% of their sample of wild turkeys had residue of the pesticide in their livers. Turkeys in agricultural areas, as the studied turkeys were, tend to eat seeds from farmers’ fields; those can easily be neonic-treated seeds. In addition, they may consume insects that have been contaminated with the pesticide; and when predators chow down on those turkeys, the residue of the pesticide moves up the food chain.
Evidence continues to emerge that such contamination of one aspect of an ecosystem can ripple throughout the system and portend other dynamics harmful to the balanced functioning of the system. Such ripples are an example of what’s known as a “trophic cascade” — a series of indirect ecosystem effects set off by a change in the status or abundance of a predator or prey organism. For example, decline in a bird population due to one or more factors (pesticides, habitat loss, et al.) might lead to: overgrowth of populations of prey insects on which the birds typically feed; greater destruction of plants (whether trees or agricultural crops) by those insects; increases in other populations that feed on the same insects (e.g., bats) and/or on the damaged plants — essentially, a destabilization of the equilibrium and well-being of the ecosystem.
Beyond Pesticides continues to work to raise awareness about the dangers to wildlife and the wider environment that pesticides pose. Learn more about what you can do in your community to protect pollinators and other species impacted by pesticides, and by neonicotinoids, in particular, via the short video, “Seeds that Poison.” More broadly, organic solutions to pest management and land management are the best ways to protect bird and non-target wildlife populations. On the home front, there are alternatives to toxic neonics. Commercially, we can manage land used for food production without the use of toxic pesticides by moving to organic practices, which forgo pesticide use in favor of cultural practices that improve soil health and enhance natural ecosystem processes. For more information on organic land management see the recent article in Pesticides and You titled “Thinking Holistically When Making Land Management Decisions.”