what's when in las islas?
There is not really a "best" time of year to visit the Galapagos - the archipelago is always magical. There are 2 distinct seasons however. From around the first of the year through roughly May is the "hot and rainy" season. During this time you can expect daytime temperatures to be in the upper 80's/mid-90's (30-36c) with the evenings in the mid 60's (17-19c). Average rain this time of year is typically 15 to 20 minutes, every 2 or 3 days, mixed with bright sunny days and blue skies. Humidity isn't too bad at any time. The ocean is the calmest, flattest, clearest, and warmest this time of year - water temperature average is around 74-76 degrees (24c).
Around the middle of May the ocean currents will change and the annual upwelling will resume. This colder water reaching the surface brings with it the change of seasons - the start of the "garua" (mist) season. Mist will be common at the upper elevations of the volcanoes, but fairly unusual at sea level. Rain is virtually unheard of, but there may be some light overcast. Temperatures will be about 10 degrees cooler; upper 70's/lower 80's (24-28c) during the day, and mid to upper-50's (13c) at night. This cooler ocean, averaging 66-70 degrees (19-21c), is richer with more particulate matter (nutrients!) and fish.
Galapagos flora responds to the rainfall, with the environment being lusher and greener typically between February and June. The rest of the year the islands will have a more stereotypical desert island appearance, with many of the remarkable plant adaptations to the environment obvious.
There is only one migratory species in the islands; the waved albatross. They are not present January-March (the males typically return the last week of March, with the females returning the first week of April). Other seasonal changes include more breeding activity for the land birds (Darwin's Finches, Galapagos Mockingbirds, Galapagos Doves, etc) during the first half of the year (due to increased precipitation, and therefore increased plant growth). During the latter half of the year there is apt to be more activity among the sea birds (the cooler, richer, water bringing an increase in the number of fish, which in turn prompts activity amongst any opportunistic breeders in the seabird colonies). Other seabirds, like the great frigatebird, are seasonal, with courtship and display peaking in the spring (April and May typically). Blue footed and red footed boobies tend to court and breed year round, as do magnificent frigatebirds, although again, they are opportunistic. Nazca boobies are more seasonal, with nesting happening between October and March. The majority of sea lion pups are born in the fall, with the pups reaching their most playful stages when snorkeling with us in the spring and early summer. Giant tortoises follow the moisture, so tend to be at lower elevations in the first half of the year, and higher elevations (where we are more apt to find them) later in the year. Marine iguanas court and nest in the December-February time frame.
Following is a very abbreviated species list highlighting a few of these seasonal differences. As with all nature, there are no guarantees, although the Galapagos are remarkably predictable. Every year/season is unique however, which is part of the fun! Endemic species included on this list are noted with an *
Range restricted species...
More important than when you go to Galapagos, is really where you go in Galapagos. You want a voyage long enough to take in as many of the islands and visitor sites as possible (which is why we spend either 11 or 15 days aboard the yacht in Galapagos). Each island is unique, with its own remarkable flora and fauna. If you don't go north to Tower/Genovesa your chances of seeing Red-footed Boobies are slim. Don't go west to Isabela and Fernandina and you'll likely miss the Flightless Cormorants, Galapagos Penguins, Mola-mola, and more. If you bypass Santiago you'll not get close to Fur Seals or the best tide pools. Santa Fe is the only home to one land iguana species (and probably your only chance to see the endemic Rice Rat). Bypass Espanola and you'll miss the Waved Albatross...