corticosterone

Corticosterone is a steroid hormone in the glucocorticoid family—essentially, it's a chemical messenger that travels through the bloodstream to influence cells throughout the body. It's most prominently known as a key stress hormone in birds and rodents, and it is also the main glucocorticoid in many reptiles and amphibians. In many other animals (including most fish and many mammals), cortisol is the dominant glucocorticoid instead.

When an animal encounters a stressful situation—a predator, lack of food, social conflict—the brain activates the stress-response system (often described as the HPA axis: hypothalamus → pituitary → adrenal glands). Signals from this pathway stimulate the adrenal cortex to produce corticosterone. This surge prepares the body for action by increasing glucose availability (energy!), dialing down non-urgent processes like digestion and reproduction, and sharpening attention.

However, prolonged or chronic stress can keep corticosterone levels elevated, which may harm health over time. Possible effects include weaker immune responses, changes in learning and memory, disrupted sleep and daily rhythms, and shifts in body condition. Researchers often measure corticosterone in blood, saliva, feces, feathers, or hair to estimate an individual's stress load and to understand how environmental factors affect well-being.

Interestingly, while humans primarily use cortisol as a stress hormone, we do produce some corticosterone—it's just not the dominant player, and it also sits along the pathway that leads to aldosterone (a hormone involved in salt and water balance). Understanding corticosterone is useful for anyone studying animal behavior, physiology, or ecology, because it offers a window into how animals cope with challenges and maintain balance in a stressful world.