Colombias cotton-top tamarin monkeys weigh just one pound and are tiny enough to sit in your hand. You can see why they might need a little help fighting off poachers and other threats. For todays Call of the Wildlecture, Rosamira Guillen, project director for Proyector Titi, along with Anne Savage, conservation biologist for Disney Animal Kingdom, will discuss their efforts to protect the tamarins and what you can do to help. 7 p.m. Houston Zoo, 1513 North MacGregor. For information, call 713-533-6500 or visit www.houstonzoo.org. $5 to $15.