BOSTON — The lion was panting. The tigers were gnawing at blood-flavored ice pops. And as the temperature approached 90 on Thursday at the Franklin Park Zoo, Jockamo the anteater was basking in the chilly spray of a garden hose, courtesy of Jeannine Jackle, one of his keepers.

Ms. Jackle and her fellow zookeepers were also wilting in the heat, but they said it was the animals they had to look out for.

“Obviously, your vigilance has to be increased on a day like today,” said John Piazza, the zoo’s mammal curator.