Lisa said that this has been an email and reference desk question.
We have two subscription databases to help students answer this question:
CCH Accounting Research Manager and RIA Checkpoint, in which you search the Accounting, Corporate Finance and Auditing information.
In either database, you can select GASB, the government accounting standards board.
I tried a keyword search zoo and animal and depreciation.
If the students scroll down through the information, they will find the answer.
If you do a simple keyword search in CCH Accounting Research Manager, there is also interpretative information (Miller GASB Guide) available. The beige background indicates interpretative information.
I also did a Google search and realized that there are different types of zoos. The GASB standards would be applicable to nonprofit zoos, such as those operated by cities. Zoos operated as private commercial enterprises, for a profit, might raise other questions, and the FASB guidelines should then be consulted. (The Google answer by a CPA for a petting zoo operated as a commercial business distinguished between animals born at the zoo and those purchased for the zoo and perhaps later sold.) So, students might need to do some more research. A number of zoos post their annual reports on their web sites.
I hope this information is helpful.