After 10 days of ship travel, at last we reached the entrance to the Panama Canal and our passage to the Atlantic Ocean and Caribbean. It took almost 12 hours to transit the 50 miles of the canal, through three sets of locks on the Pacific side, into huge Lake Gatun, and then through three sets of locks on the Atlantic side.
I was particularly interested in getting a look at the islands in Lake Gatun, which was formed by damming the Chagras River at a narrow point near its mouth on the Atlantic side (see map below near Gatun locks) back in 1913. When dammed, the river then flooded a once wide valley forming a large lake with just the mountain tops projecting up forming a series of small and large islands in the lake.
This area of Panama receives about 100 inches (i.e., 8 feet!) of rain annually, but almost all comes during the rainy season. During the dry season between December and April, less than 3 inches of rain falls and many of the island streams dry up. The soil becomes so dry, large cracks develop in it. Flowers and insects disappear, trees stop producing fruit, and animals on the island become food limited.
As a result of changes in the forest structure with limited island land surface and the size of the islands themselves, species diversity of animals, and especially birds, is markedly lower than that of intact rainforest on the hillsides of the canal — as you would expect. Researchers have found smaller numbers of under-story bird and mammal species, and there are no large mammalian carnivores to control the herbivore populations. But food is a limiting factor here.
National Geographic produced an interesting video featuring some of the work that has been done on Barro Colorado Island in 2007: Panama Wild — Rainforest of Life. If you like nature videos and want to know more about this area of the world — click on the video below.