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Ospreys and their recovery


by Courtney Collins

Ospreys (Pandion haliaetus) can be found across Canada during the summer breeding season. Ospreys are migratory and can travel over 250,000 km throughout their relatively long lifespans. These beautiful dark brown and white raptors are unique for their fishing habits – a necessary ability to maintain their diet of, nearly exclusively, live fish.1 While these birds-of-prey have healthy population numbers today, it wasn’t so long ago that the story was drastically different. From the 1950’s through 1970’s, osprey populations plummeted to severely low numbers, with some local populations even becoming extinct.2 This was directly caused by the pesticide (insecticide) DDT (dichlorodiphenyltrichloroethane).3 Many bird species were impacted by DDT, and extreme population declines prompted the release of the book Silent Spring from Rachel Carson in 1962, which documented the harmful impacts of widespread synthetic pesticide use. Upon the release of Silent Spring, the American public in particular, were made aware of the environmental costs of pesticides.4
Osprey patient in care at AIWC (2017).
Unfortunately, DDT is not biodegradable and becomes concentrated in the environment, and as it does so, it ’moves up’ the food chain – for example, when an earthworm is in contact with DDT and a robin consumes the earthworm, it can become poisoned by said DDT. When a larger bird of prey consumes various prey species, all of which have been poisoned by DDT, the bird of prey has now consumed a greater amount than each individual organism it has consumed – thereby magnifying its toxicity.5,6 Furthermore, DDT built up within the body of many larger organisms, including ospreys.7 This process is called biomagnification and means that every organism in the food chain from insect to top predator is impacted by the toxic effects of DDT.8 For ospreys (and other birds of prey), DDT caused poisoning, but also had toxic impacts on calcium metabolism – meaning that (among other impacts) eggshells were not strong enough to bear the weight of the incubating bird, ultimately leading to severe populations declines across many species.9
Airplane spraying DDT over forest in Oregon, 1955 (Public Domain).

Although Silent Spring was released in 1962, it was still a decade or more prior to DDT being phased out or banned. The sale and use of DDT was banned in 1972 in the United States and was phased out in Canada during the mid-1970’s, with a complete discontinuation in 1990.10 After the phasing out of DDT, osprey populations began to rebound, increasing by ~1.9% annually until 2019 in North America.11 While this is an incredible conservation success, it is important to remain vigilant about pesticide use and recognise that these compounds can have a rapid and detrimental impact on species other than those targeted. Although ospreys are currently listed as having a low risk of becoming endangered in Canada, other threats including pollution and loss of habitat have begun to impact these magnificent birds and should not be ignored.12

You can find this amazing species across Alberta during the summer months near water bodies – if you’re lucky you may even get to see their incredible hunting techniques when they dive to catch a fish.


  1. All About Birds, “Osprey”, The Cornell Lab, n.d.

  2.  Peter J. Ewins, “The Fall and Rise of Osprey Populations in the Great Lakes Basin”, Environment Canada Ontario Region, 1994.

  3.  Pete Dunne, “Now Resurgent, Ospreys Once Faced an Uncertain Future”, Audubon, 2018.

  4. Wikipedia, “Silent Spring”, Wikipedia, 2024.

  5. Gokul G. K., “Biomagnification – An Ever-growing Threat”, WCS-India, 2020.

  6.  Paul Ehrlich, David S. Dobkin, and Darryl Wheye, “DDT and Birds”, Stanford, 1988.

  7. William Freedberg, “Conservation Success Stories: The Osprey”, Mass Audubon, 2018.

  8. Gokul G. K., “Biomagnification – An Ever-growing Threat”, WCS-India, 2020.,accumulated%20in%20the%20higher%20organism.

  9. Paul Ehrlich, David S. Dobkin, and Darryl Wheye, “DDT and Birds”, Stanford, 1988.

  10. North American Commission for Environmental Cooperation, “History of DDT in North America to 1997”, Commission for Environmental Cooperation, n.d. 

  11. All About Birds, “Osprey Life History”, The Cornell Lab, n.d.
  12. Nature Canada, “Get To Know This Year’s Featured World Migratory Bird Day Species: Osprey”, Nature Canada, 2023. 

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