More pets died on Delta Air Lines than on any other carrier last year, according to data released by the federal government.
Out of 35 pets that died on airlines last year, 19 died on Delta flights. That's up from 16 the previous year.
Delta said it carries more pets than many other airlines, in part because of its broad route network. The number of pets that are injured or die on the airline is less than 0.2 percent of pets carried, Delta said.
Many carriers such as AirTran and Southwest don't carry pets as checked baggage in the cargo hold. Some pets also are transported in the cabin as carry-ons, but the deaths were all in the hold.
"The loss of any pet is unacceptable to us," Delta spokesman Anthony Black said. "We are working to improve the processes and procedures to ensure that every pet arrives safely at its destination."
One of Delta's latest changes came in December, when it stopped accepting snub-nosed dogs or cats as checked items. Delta already had banned American, English and French bulldogs from flying. That came after a sharp increase in the number of animals that ran into trouble on Delta flights, particularly bulldogs, which are susceptible to respiratory problems.
In most cases, pet deaths are not caused by mishandling but because the pets run into health issues in the cargo hold environment, Delta said. The Humane Society of the United States recommends not transporting pets by air "unless absolutely necessary" because of the risks.