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The main target of this extension to the Beni -- the rare and beautiful Blue-throated Macaw, here at home in an Atalea palm grove. (Photo by guide Dan Lane)

What is “The Beni” and why is it so durned special? Well, it’s believed that over a million years ago, much of the southwestern Amazon basin was occupied by an inland sea. Over the millennia, as the Andes rose, this sea started to recede, draining out through the proto-Amazon. The last of this sea was left in the present-day Beni, a low-lying area that drained through the bottleneck of the geologic arch on what is the present-day Rio Madeira, just inside Brazil. Today, the Beni still becomes a large lake during the rainy season, but drains for the most part during the dry season, as we saw. While it was still a body of water, it is conjectured that there were nevertheless some higher lands that existed within it as islands. These islands probably were vegetated with a forest reminiscent of ‘varzea’ present today in much of Amazonia, and birds related to species found in Amazonian varzea were isolated on these islands long enough to differentiate. As the Beni “dried out”, an Amazonian influence was able to extend up the gallery forests along the larger rivers that drained it (particularly the Rio Mamore), but others were excluded by the presence of competitors already present in the area. Meanwhile, the floodplain became vegetated by plants that are shared with the Pantanal, an adjacent region that probably shared a similar history (although is not connected directly to the Amazon), resulting in the palm-dominated savanna we see there today.

“Lake Beni” was inhabited by the Amazon River Dolphin, but because of the continued presence of the rocky arch on the Rio Madeira, forming rapids today, the Beni population and that in the Amazon proper have became isolated, and now two taxa exist: species in the eyes of some mammalogists. Similar things happened to several birds such as Plain Softtail, Velvet-fronted Grackle, Varzea and Unicolored thrushes, and a pair of macaws with blue and yellow plumage. The first three are not all that strongly differentiated -- the Amazonian and Beni forms of the first two are, as you can see, still considered conspecifics, but further study is likely to overturn that status. The last pair is more clearly differentiated and, more importantly, are now found together without interbreeding…clear evidence that they cannot be considered conspecifics! Sadly, the present-day co-occurrence of Blue-throated and Blue-and-yellow macaws may be the undoing of the former. The larger and more aggressive Blue-and-yellow Macaw occupies a similar niche to its smaller cousin and, worse still, seems to be capable of muscling it out of breeding sites. The smaller Blue-throated Macaw, to its disadvantage, is also more specialized than its larger relative, requiring large stands of the Atalea palm for foraging and nesting places. It was in such a place that we went to see the pair we enjoyed. Of course, the interest in the rarer macaw by the pet trade hasn’t helped this bird, either. With luck, ecotourism may help bring conservation dollars in to help it withstand these perils and continue to screech amid the Beni's palms.

But the Beni is more than a land with a few specialized birds! As we found, it is in fact a very birdy place, what with all the large waterbirds, the screamers, the limpkins, the storks, the ducks, the skimmers and terns, and then there are the parrots, parakeets, pigeons, ground-doves, finches, horneros, cachalotes, woodpeckers, woodcreepers, spinetails…well, you get the idea! In less than four days, we saw about half the number of species we enjoyed on the following two weeks on the main Bolivia tour! Wow, that’s some bird biomass! And let’s not forget the caimans, capybaras, foxes, and that incredible experience watching the mating tangle of anacondas! Yes sir, the Beni is a pretty special place. I know I enjoyed the visit, and I hope you all did too. Keep those binoculars handy, and maybe see you again soon on another tour!

--Dan

KEYS FOR THIS LIST
One of the following keys may be shown in brackets for individual species as appropriate: * = heard only, I = introduced, E = endemic, N = nesting, a = austral migrant, b = boreal migrant

ADDITIONAL COMMENTS

Bat sp.

Tegu Lizard (Tupinambis sp.)

Spectacled Caiman (Caiman crocodilus)

Green Anaconda (Eunectes murinus)

Toilet Seat Frog (Trachycephalus typhonius)

Cane Toad (Bufo marinus)

'Leopard' Frog (Leptodactylus sp.)

Totals for the tour: 234 bird taxa and 6 mammal taxa