Future Callout with apex trigger for a webservice

 if(System.IsBatch() == false && System.isFuture() == false){ 

 Error if this above condition is not used in trigger: System.AsyncException: Future method cannot be called from a future or batch method: herokuapp.animalname(String)

Animal__c is a string field to update a value of o index from the webservice call.

Trigger: 

trigger herokuapp_account on Account (after update) {

    for(account a: trigger.new)

    {

        if(System.IsBatch() == false && System.isFuture() == false){ 

            if(trigger.isUpdate)

            {

                herokuapp.animalname(a.id);

            }

        }

    }

}

Trigger Handler 

public with sharing class herokuapp {

    @future(callout=true)

    public static void animalname(string id)

    {

        Http http = new Http();

        HttpRequest request = new HttpRequest();

        request.setEndpoint('https://th-apex-http-callout.herokuapp.com/animals');

        request.setMethod('GET');

        HttpResponse response = http.send(request);

        // If the request is successful, parse the JSON response.

        if (response.getStatusCode() == 200) {

            // Deserialize the JSON string into collections of primitive data types.

            Map<String, Object> results = (Map<String, Object>) JSON.deserializeUntyped(response.getBody());

            // Cast the values in the 'animals' key as a list

            List<Object> animals = (List<Object>) results.get('animals');

            System.debug('Received the following animals:');

            Account a=new Account();

            integer i=0;

            List<Account> aList=new List<Account>();

            string animalname=animals[0].toString();

            system.debug('animalname'+animalname);

            a.id=id;

            a.Animal__c=animalname;

            system.debug(a);

            update a;

        }

    }

}