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  • Erin Shaotran

The Persistence of the Cal Falcons: Surviving Through DDT and Climate Change

By Erin Shaotran



Peregrine falcons are known as one of the fastest birds of prey due to their impressive flying speeds and hunting abilities. Unfortunately, peregrine falcon populations are on a national decline and a family of peregrine falcons nesting at the Campanile in UC Berkeley is a rare sight today. This rarity is due to climate change, decreasing habitat space, and the bioaccumulation of DDT, a toxic chemical that affects the health and population of animals along with the impacts of climate change.


DDT (dichloro-diphenyl-trichloroethane) is a synthetic insecticide that was widely used to control insect populations in the 1940s and 1950s. DDT was widely used in the mid-20th century to control insect pests, especially mosquitoes, that transmit diseases such as malaria and typhus. DDT was first synthesized in 1874 but its insecticidal properties were discovered in 1939. It was effective in reducing insect populations, but was later found to be harmful to humans and wildlife. During the 1960s and 1970s, the peregrine falcon population dropped and falcons were considered an endangered species. DDT was discovered to persist in the environment and can travel long distances in the upper atmosphere. However, one of its worst effects is that it can persist for decades in the environment and accumulate in animal tissues over time. Because of these negative effects, the United States banned DDT in 1972, but extensive damage had already been done. Birds of prey, such as peregrine falcons, are particularly affected by DDT biomagnification. Biomagnification occurs when the concentration of a chemical increases higher up in the food chain. Since falcons are at the top of the food chain, they accumulate the most amount of these chemicals compared to most other animals.


DDT has major negative effects on peregrine falcons. One of these effects is that it causes eggs to be significantly more fragile, making embryos susceptible to breakage and preemptive lethal exposure to the outside world. This is known as eggshell thinning. Most falcon parents exposed to DDT died, and their eggs were unable to develop in the embryo as a result of this thinning. If the babies did survive, a disproportionately larger number of them were female compared to male. This is called feminization, in which endocrine-disrupting chemicals (EDCs) mimic hormones within the falcons’ body, permanently altering the falcons’ sex. Furthermore, most falcons exposed to DDT or borne from parents exposed to DDT had reduced fertility. These effects resulted in a significant reduction of the falcon population.


Despite the impacts of DDT, the falcon populations are nonetheless beginning to recover from the impact of DDT after its 1972 ban. In fact, peregrine falcons were removed from the federal endangered species list in 1999. When peregrine falcon deaths due to DDT were at its peak, services such as the National Park Service’s Peregrine Falcon Recovery Program helped falcons by feeding them clean foods and reintroducing them into the wild. There was also an initiative to protect falcon nesting sites. The combination of these programs and DDT’s ban, allowed for less DDT accumulation in the food chain, further resulting in a significantly lower amount of falcons being impacted by its effect. Although DDT lingers within soils today, falcons are less impacted by its effects.


Unfortunately, falcons must also deal with the impacts of climate change. Climate change can affect peregrine falcons’ migratory patterns for several reasons. Climate change can lead to changes in plant and wildlife distribution, including falcons and the species they depend on for their survival. As a result, their habitats may shift, shrink or disappear, reducing the availability of suitable nesting sites, roosting areas, and prey. Changes in weather patterns, such as changes in precipitation, temperature, and wind patterns, can impact the availability and abundance of their prey. This can affect their hunting success rates, survival rates, reproductive success and more. Falcons breed during specific times of the year when climate conditions are favorable for nesting and rearing their young. Changes in weather patterns can cause these conditions to shift, which can affect the timing and success of breeding. Additionally, changes in habitat and food availability can also cause falcons to come into competition with other species that are adapting to the changing environment. This can further stress their populations and limit their ability to adapt.


Despite all these struggles, the falcons at UC Berkeley constantly grow their family. Pictured above, the family’s matriarch, Annie, laid four eggs just a few weeks ago! Even though they aren’t immune to the effects of climate change, habitat loss, and DDT, their continuous survival is celebrated by the community. UC Berkeley has launched a program to monitor and protect peregrine falcons on campus. The program includes a group of scientists from the university who monitor the family and a 24/7 falcon camera, in which the community can watch the family whenever they please. There’s an instagram page, cal falcon merch, and a website dedicated to the beloved and ever-changing family. The falcons have become an integral part of the Cal community, as the successes and losses within this falcon family are celebrated and mourned alike. For instance, there’s a naming contest each time new eggs are laid and each falcon is named after an honorable person from cal. We must continue to monitor and protect falcons and work to prevent further environmental damage to them at all costs if we want them to survive and flourish in the future.



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