Splitting Birds in Two   3 comments

Felipe del Bosque Blog Oct 03 2010

Temp High 92°F  Low 73°F          Precipitation 1.25 ins

Today was grey, overcast and misty with showers.  That made it a very quiet start to the day.  But that is how the day remained, the mist transformed into rain and then back to mist again, eventually with less mist and more of a constant downpour.

Bay-headed and Golden-hooded Tanagers are generally found flying in small flocks, quite often together.  There is one other species of tanager you will commonly see in the gardens at the front of the restaurant, Cherrie’s Tanager.  These are very handsome birds, the males being a deep velvety black with a bright red back and a silvery blue bill; the females are an orangey brown.  Cherrie’s Tanagers are normally seen in small flocks consisting of a male escorting a harem of females.

Until recently the birds were called Scarlet-rumped Tanagers, a name which literally described the strikingly colored males.  But with the birds, taxonomically, the splitters have been at work.  This particular species was split into two; Cherrie’s Tanager which is found on the Pacific Coast and Passerini’s Tanager which is found on the Caribbean coast.  The males are identical but females have a slight difference in coloration between the two coasts which warranted them being split into two species.

A similar situation occurred with the Long-billed Hermit, a hummingbird that has a long bill and a long tail.  It used to be known as the Long-tailed Hermit but now that name only applies to the birds found south and east of the Andes, while to the north and west it is now the Long-billed Hermit.

Positioned stationary about 100 foot above my head, riding an updraft from the cliff edge was a Mangrove Black Hawk.  Its position was maintain by delicate movements of the tail and wings, finely honed avionics hardwired into the birds brain.  The black hawks are usually encountered down on the beach, perched in low trees, scanning the rocks, then swooping down to catch and feed on a crab, which form a large part of their diet.  It shifted direction, moving a hundred yards to its left, stayed there for a matter of minutes, then drew its wings into its sides and plummeted out of the sky, opened its wings once again and glided away through the trees.

One of the things that makes birds such excellent fliers, veritable masters of the air, is that they are so aerodynamically unstable.  A single movement of the tail or wing tip will send the bird into a three dimensional spatially different realm.

The black hawk too, has been the victim of the splitters.  It is yet another literally described bird, it is a hawk and it is black, apart from a white tail band that is, so a black hawk.  On the basis of the length of the bone in the forearm we know have the Mangrove Black Hawk on the Pacific and the Common Black Hawk on the Caribbean.  I would defy you to tell the difference between any of the above 3 pairs of birds should you leave Bosque and continue your journey on the east coast.

Philip is a biologist, writer and photographer as well as the onsite naturalist guide at Bosque del Cabo Rainforest lodge on the Osa Peninsula, Costa Rica.


Photo Feature

Leaf-cutter Ant Trail

I think, without exception, everyone who visits Bosque del Cabo has seen Leaf-cutter Ants.  You can stand and watch them excavating material from nests that, in ant terms, cover vast, metropolis sized areas.  Most people marvel at the length of the ant trails, cutting swaths through the lawns or traversing the forest floor on pathways that put our level of trail clearance to shame.  If you follow the ant trail back along its course in the reverse direction to which the leaves are being carried, you will see the ascending 100 foot up into the crown of the tree, and then descend carrying a cut fragment of leaf that both out sizes and outweighs its six-legged transporter.  Who would have thought it, but Leaf-cutter Ants are quite often the highlight of a trip to the tropics.

Waste Disposal at the Nest Entrance

When you see the river of green running along on the forest floor, don’t imagine that the ants have gone to all that trouble to collect leaf to feed upon.  The Leaf-cutter Ants are mycovores, they eat fungus.  The leaves are collected, taken back to the nest and then processed into a mulch upon which they grow a certain species of fungus.  The fungus does what the ants cannot; it breaks down the plant material and then the ants feed on the fungus.  The fungus doesn’t grow anywhere outside of leaf cutter nests and the ants don’t eat anything other than the fungus which makes the two organisms mutually reliant upon each other for survival.

Leaf-cutter Ants - Olympian by any Comparison

When the ants leave the nest to go and cut the leaf, they are doing the equivalent of a 3.5 minute mile, they cut and carry something 3 – 5 times their own body weight and return doing the equivalent of a 4 minute mile.  This they do over a course that in relative terms is 10’s of miles long, 100 foot up into the tree tops, 2 or 3 times a day, 24 hours a day, 7 days a week.  By way of an analogy; if you could imagine never going to bed, doing 2 or 3 marathons a day, at the pace of a sprint, with someone 5 times your own body weight sitting on your shoulders, over an obstacle course and up the side of a mountain, you will then start to understand why people find Leaf-cutter Ants so compelling to watch.

Text and Photographs are taken from the forthcoming book:

The Natural History of Bosque del Cabo by Philip Davison

Species List for the Day


Howler Monkey

White-nosed Coati



Red-lored Amazon

Scarlet Macaws

Chestnut-backed Antbird

Black-hooded Antshrike

Chestnut-mandibled Toucan

Cherrie’s Tanager

Bay-headed Tanager

Golden-hooded Tanager

Mangrove Black Hawk

Great Tinamou

Turkey Vulture


Northern Cat-eyed Snake


Marine Toad

Red-eyed Green Treefrog

Parachuting Red-eyed Green Treefrog

Banana Frog

Olive Treefrog

Masked Smilisca

Tink Frog


Heliconius sapho

Urbanus proteus


Posted October 4, 2010 by felipedelbosque in Philip's Nature Diary

3 responses to “Splitting Birds in Two

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  1. Nice stuff Phillipe! Long time. Short time.


  2. Looking forward to your return!


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