The Jaguar Rescue Center is a non-profit, humane-society organization in Puerto Vejo. They accept any animal brought to them from the local communities. Their operation is a recover and release one where they will nurse injured or seperated animals to the point that they can be released back into the wild. Because of this you really can't expect to see any animal in particular when you arrive. However, if you are coming from an area that has access to powdered goat's milk, they would be more than happy to accept it since they can not obtain any locally and it is used for nursing animals such as sloths.
The center also owns a portion of jungle that is not avaliable for tours. This area is where they re-introduce the animals in a "controled" manner that is guarded 24-7 to protect the animals from poachers. The tour is in an entirely outside (though partially covered) environment where you can intereact with the animals including baby howler monkeys and occasionally baby sloths. However, be warned that the monkeys love to play with loose items you may have (sunglasses, cameras, necklaces) and that it will be hot so bring water if you are not used to the high temperatures. The tour guides speak will speak English or give the tour in Spanish and English. They are all very knowledgeable and will help you throughout the tour.