How do animals react to a solar eclipse?

Most reports of animal behaviour during an eclipse are anecdotal, but it is clear that some animals do react unusually during solar events. When an eclipse occurs, even though it’s technically daytime, many animals will start to behave as they normally would at nightfall and begin their typical evening routine.

Both solar and lunar tidal cycles are closely tied to a number of hormonal systems. Much ink has been spilled about the effects of melatonin on our sleep cycles, for example. But melatonin also helps regulate many other important hormonal systems in the animal kingdom, including reproductive activity, moulting, hunting and feeding habits. Light levels can therefore affect wildlife responses in a variety of ways.

But behavioural changes that manifest during an eclipse are transient, so it’s hard to study them or identify patterns.

Birds, mammals and even some insects have been known to exhibit atypical behaviours. For example, birds that are normally active during the day will stop singing, just as they do at dusk. Some frogs will start their evening croaking. Bats may also wake up and take wing as if night had fallen. One report describes hippos in Africa beginning to withdraw from their daytime riverbeds during an eclipse. Some species of arthropods in South America have been seen breaking down their webs, which they normally do in the evening.

Basically, these are all typical behaviours; they’re just not occurring when they normally would.

The greatest threat comes from the potential increase in human-animal interactions. Typically nocturnal animals may emerge, and diurnal species return to their dens, at times when humans are still very active. It can be dangerous for both animals and humans. For example, an increase in animal roadkill was reported in the United States during one eclipse.

Waking during an eclipse might not impact healthy bat populations but it can have a detrimental effect on bats whose systems are already weakened, such as those afflicted with white-nose syndrome. As they won’t be able to feed during the short period they’re active during the eclipse, they are wasting precious energy.

There have been no reports of eye damage in primates following eclipses. But if I were working with primates in a zoo, I’d give them the option of returning to their indoor enclosures during an eclipse to allow them to express their usual nocturnal behaviour. But primates looking at the sun is not something that is well documented and there have been no reports of blindness. I don’t think it should be cause for alarm.

It seems plausible that animals will exhibit more extended behavioural changes in areas that stay dark for longer. But the evidence is still largely anecdotal. We don’t have enough hard data to back up our observations. Cold-blooded animals, such as reptiles and fish, may experience a temporary decrease in their metabolism during the eclipse, as their internal temperature is directly affected by ambient temperatures. But I doubt that brief behavioural changes, say for 15 minutes or so, will truly impact their survival. Long-term environmental changes, such as global warming, are far more likely to have lasting effects on their behaviour and survival.