Why did peregrine falcon populations decline after World War II?

Following World War II, peregrine falcon populations experienced a precipitous global decline primarily due to the widespread use of pesticides, specifically DDT and dieldrin.12

The decline was driven by the following factors:

• Eggshell Thinning: Peregrine falcons ingested DDT through their avian prey. This chemical concentrated in the birds' tissues and interfered with calcium deposition, resulting in abnormally thin eggshells. These fragile shells were prone to breakage during incubation, leading to reproductive failure.13
• Direct Mortality: In regions such as the British Isles, the pesticide dieldrin was identified as a primary cause of the decline due to its role in direct mortality.1

These toxic chemicals posed a severe conservation challenge because of their subtle, widespread environmental impact. Following the restriction or banning of these organochlorine pesticides, populations have since rebounded globally.21