Veterinarians at Monterey Bay Aquarium may have discovered what killed three penguins at the facility two months ago. In November, the endangered penguins died unexpectedly, prompting the closure of the exhibit for two days. After evaluating the birds, veterinarians believe their deaths may have been caused by a toxic reaction to an antifungal drug. This type of medication has been associated with toxicity in other bird species. The drug is not being given to the remaining penguins in the exhibit, as a precaution.