Who knew that coprophagy was so vital for birds' survival?

Faeces -- either their own, or from other birds -- provides them with essential nutrients, energy, and helps them adapt to new environments and seasonal variations, especially when they are developing.

New research led by the University of South Australia and published in Biological Reviews explains how eating faeces (known as coprophagy) shapes wild birds' digestive tracts (gut biota), enabling them to absorb lost or deficient nutrients and adjust to seasonal variations in food sources.

This is especially important for long-migratory birds, which transition between fasting and fuelling metabolic states as they fly around the world.

Lead author Dr Barbara Drigo, a UniSA microbial ecologist, says consuming faeces modifies bacteria and microbes in the birds' digestive tract, allowing them to adapt to new environments.

There is also some evidence that ingesting faeces could be a form of self-medication to fight infections in birds, although more research is needed to confirm this theory.

While coprophagy provides birds with essential nutrients, it also has a downside, Dr Drigo says, because birds can potentially harbour and transmit diseases to other birds and humans via their faeces.

"Depending on their geographical range, behaviour and interactions with other animals and environments, birds -- especially migratory ones -- can efficiently spread pathogens around the world.

"Eating bird faeces may also increase their exposure to antimicrobials, particularly pesticides and cleaning products, which lead to antimicrobial resistance," Dr Drigo says.

And the reason why humans should never feed bread to birds is that it lowers diversity in their gut microbiota, whereas if birds source food from natural sites, their digestive tract is much healthier.

"Birds foraging in human environments are exposed to chemicals and metals from waste, sewage and refuse, which can alter their microbiota, potentially leading to antimicrobial resistance."

Dr Drigo says a healthy avian gut is essential for regulating birds' biological functions, and eating faeces plays a significant role in this. However, while coprophagy is inherently beneficial, it can expose birds to harmful antimicrobial substances.

"There's an urgent need to thoroughly explore how various forms of coprophagy impact avian gut microbiomes, affecting bird health across their different life stages and environments," she says.