Don't only humans have the ability to enter social
contracts?
Other animals do agree to certain types of social contracts with
each other. For example, some species of bats share the food they
find with others in their community who they are not related to.
It is not possible to force a bat to share against his will,
since this process is done by regurgitating food directly into
the mount of the recipient. Each bat remembers which individuals
in the community have helped them when they themselves were
hungry, and they remember which individuals refused to help them
in their time of need, and these bats respond in kind.
It is not unusual for a bat to be unable to find food for several days, in which case his survival depends on having friends. In effect, by sharing food with others, these bats are purchasing an insurance policy. A bat with a large network of friends is much more likely to survive - and a bat who chooses not to honor his contracts (not help those who have helped him in the past) will soon find himself without any friends when he is in need of assistance.
Follow up questions:
What do we gain by respecting the rights of other animals if they do not respect our rights?
Aren't only humans self aware?
What evidence is there that other animals can make moral decisions?
Don't only human beings have a soul?
Don't only humans have the ability to use language and understand abstract concepts?
How do you know that other animals can feel pain?
Don't only humans have the ability to pass on cultural information from one generation to the next?
Don't only humans understand the concept of death?
Don't only humans have the ability to use tools?
How can some animal rights activists believe that other animals are our equals?