The light was beginning to fade and Hassan, the lion, knew what that meant.

It was time to kick off his bedtime behavior with a leisurely patrol around his enclosure at the Maryland Zoo in Baltimore. The 16-year-old big cat opened his maw and tasted the air just like he did most evenings.

Hassan’s caretakers usually dropped off dinner when the sunlight waned and the temperature dropped — but where were they? The lion chuffed. One low growl was followed by another and another, like a steam engine picking up speed.

The roaring routine was premature. Turns out, it wasn’t bedtime after all.

The North American solar eclipse was partially visible over parts of Maryland Monday afternoon, with the moon blocking about 80% to 90% of the sun over the state by 3:21 p.m. While eclipses have long delighted and fascinated humans, they’re also associated anecdotally with unusual behavior in other species.

[Sex at the Maryland Zoo: Bizarre facts to wow (or terrify) your Valentine’s date]

Caretakers at the Maryland Zoo kept that top of mind ahead of Monday’s eclipse. They took special precautions for species they worried could become stressed by the irregular shift in sunlight. A menagerie including zebras, chimpanzees and gazelles were moved indoors around 2 p.m.

Hassan and his mate, Zuri, were spared the restrictions but still appeared a little confused by the eclipse.

To be fair, the Homo sapiens wandering the grounds were behaving strangely, too. Most humans come to the zoo to look at animals, but around 3 p.m., were turning their backs on the lion exhibit to stare directly at the sun.

For the zoo’s general curator Margaret Innes and her colleagues, determining which animals would need special attention proved challenging. There aren’t many historical records or research on animal behavior during a total solar eclipse to consult. Innes reviewed a recent study of how the solar eclipse in 2017 affected some mammals, birds and reptiles at the Riverbanks Zoo & Garden in Columbia, South Carolina.

Three-quarters of the animals in the study appeared to change their behavior during the eclipse. The most common behavior researchers observed was mimicking an evening or nighttime behavior, suggesting the change in light and possibly temperature had served as a major cue. The baboons, gorillas, giraffes, flamingos and lorikeets appeared to show signs of anxiety, including swaying and huddling.

Innes took a conservative approach and advised caretakers to move certain species in doors beginning around 2 p.m. Chimpanzees, prone to agitation, were among them. So were the elephants.

“They notice everything,” said zoo spokesperson Mike Evitts.

As for the animals that stayed outside during the eclipse — there’s no way to know for certain what they thought of the astronomical event. Animal experts including those at the Maryland Zoo are wary of interpreting animal behavior through a human lens.

Evitts recalled the story of two ostriches who appeared to hate each other. Caretakers often observed them standing on opposite sides of their enclosure. However, it was later determined the birds were positioning themselves where they could get the clearest view of meals arriving.

In the minutes following the peak eclipse, some animals around the zoo appeared animated. Two porcupines scratched at a nearby door used by caretakers. A pair of groggy grizzlies waddled out of their den, behavior considered typical for bears exiting a winter hibernation.

Innes plans to compile a report on all of the behaviors observed among the zoo’s residents along with notes from their caretakers. Maybe it will be helpful for the next solar eclipse, she said.

By the time the moon passed by the sun, Hassan had quieted down. Dinner would be delivered eventually.