Flocking to a Disco Fight   2 comments

Felipe del Bosque Blog Sept 19th 2011

Something Strange

Not much change in the weather this week over last.  The days remain bright and sunny for the most part but with a small amount of rain falling just about every night.  It could well be that the wet season is going to bypass us completely this year or it is going to arrive with a vengeance later than usual.

Return of the Migrants

This is the time of year when all those birds that migrated north for the northern summer started to return back to their native lands for the southern summer.  Technically Costa Rica lies north of the equator and now we should be entering the winter, but here there are only two seasons wet and dry.  The worst of the wet season has yet to occur, but the temperatures remain pretty constant all year round, so even if it is not dry and sunny, it will almost certainly not be freezing either, which would be a terminal situation for most small tropical birds.

There tends to be a natural northern bias to migrating birds, people from northern latitudes regard them as their birds flying south to escape the winter whereas most of the birds migrating are from tropical bird families that have migrated north for the summer.

Why would a tropical bird leave these conditions and fly north.  The reason would be with regard to food availability for growing chicks.  The 21st of September is the vernal equinox when the earth’s position around the sun is at that point where all points on the globe receive 12 hours of daylight and 12 hours of night.  With Costa Rica lying so close to the equator, this situation does not change much over the course of the year, the longest day and the shortest day differing by approximately 45 minutes.

When the birds fly north, they now have summers where the day length is much longer, particularly the further north you fly.  This provides extended foraging time for food, which for growing chicks involves the consumption of a lot of protein, particularly in the form of insects.  Northern summers provide this huge boost in a food source in a way that the tropics don’t.  So in essence you have more available food and longer hours in which to find it.

Now the chicks have fledged it is time to return home to the tropics.  Over the past week I have seen Yellow Warblers, Prothonotary Warblers, Black and White Warblers and Mourning Warblers all in the garden areas in front of the Bosque del Cabo restaurant.

Flyweight Fight

On one afternoon stroll around the grounds I heard the sounds of an avian altercation accompanied by the frenzied buzzing of wings somewhere in a thicket off to the side of the garden.  Upon closer scrutiny I could see a Rufus-tailed Hummingbird, (Amazilia tzacatl), attempting to encourage a larger Violet-crowned Woodnymph, (Thalurania colombica), to remove itself from the area.  The subject of this dispute was a patch of Heliconias in bloom.

Heliconia sp    Heliconia sp    Heliconia sp

Heliconias are essentially a family of plants from the American tropics.  Their flowers come in variety of shapes and sizes but whatever form the blooms take, they are all colored in multifarious shades of red, orange, or yellow, colors attractive to hummingbirds.  Due to the different species of Heliconia having different shaped flowers, as the hummingbirds visit them, it results in pollen being dusted on different parts of the bird’s anatomy.  So in theory, one species of hummingbird could potentially pollinate a variety of Heliconia species.

Heliconia sp    Heliconia sp    Heliconia sp

Hummingbirds need to feed on approximately 8 times their own bodyweight everyday just to keep themselves flying, so once they find a productive food source they don’t give it up.  Rufus-tailed Hummingbirds, despite their diminutive size are very pugnacious little birds.  They will take on, challenge and expel any interlopers into their territory with gusto.

Heliconia sp    Heliconia sp

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

Rolling the Disc’s

Costa Rica is a very special little country in many respects, not one of the least is its bat diversity.  It may only encompass .03% of the land surface of the earth, but it hosts 12% of the planet’s bat species.

Around the grounds of Bosque, if you look closely, and in the right places, you will come across several different species of bat.  The Common Tent-making Bats, (Uroderma bilobatum), have their roosts under the large leafs of palms or bananas where they have ripped through the veins, causing the leaf to fold over.  These bats can be occasionally seen under various palm leaves close to the Bosque restaurant.  The continually change the location of the day roosts to avoid having their main predators, Tropical Bird-eating Snakes and Squirrel Monkeys being able to easily locate them.  They change their night roosts depending upon which of the trees are fruiting as they never forage too far from the nearest fruiting trees.

Common Tent-making Bats

Nectar feeding and fruit eating bats tend to attracted to musky smells rather than sweet smells.  Bananas are both bat pollinated and dispersed in the wild hence the flowers and fruit have that very musky smell.

On the Zapatero Trail and in small caves, both on the Pacific and Saino Trails, you may have the opportunity of seeing the White-lined Sac-Winged Bats, (Saccopteryx bilineata).  You will generally find a male with a harem of females in their typical repose of clinging head down to the sides of the tree or rock face but with the head distinctively held away.  You may be lucky enough to see the male fluttering up and down serenading his collection of female followers.

Spix's Disc-winged Bat

The third species of bat commonly found around the grounds of Bosque also uses plant leaves but this time the unfurled leaves of Heliconias, bananas and Calathea.  If you look down into one of these rolled up green cylinders, if the diameter and situation are suitable, you may see a small group of 2 or 3 Spix’s Disc-winged Bats, (Thyroptera tricolor).  The disc refers to the modified suckers on the wings which allow them to stick to the slippery inside of the leaf surface.  As opposed to other bats which roost head down, Spix’s Disc-winged Bats characteristically roost head up allowing them an easy flight up and away from danger should it threaten.

Spix's Disc-winged Bat

Text and Photographs are taken from the forthcoming book:

The Natural History of Bosque del Cabo by Philip Davison

Temperature and Rainfall

Average Daily Temp High 88°F.  Average Daily Temp Low 73°F.

Average Daily Rainfall 0.21 ins.  Total Weekly Rainfall 1.27 ins

Average Daily Temp High 30.8°C.  Average Daily Temp Low 22.8°C.

Average Daily Rainfall 5.3.  Total Weekly Rainfall 37.3 mm

Species List for the Week


  • Howler Monkey
  • Spider Monkey
  • White-faced Monkey
  • White-nosed Coati
  • Agouti
  • Red-tailed Squirrel
  • Spix’s Disc-winged Bats
  • Nine-banded Armadillo


  • Orange-chinned Parakeet
  • Red-lored Amazon
  • Scarlet Macaw
  • Great Currasow
  • Crested Caracara
  • Roadside Hawk
  • Yellow-headed Caracara
  • Golden-naped Woodpecker
  • Pale-billed Woodpecker
  • Black-hooded Antshrike
  • Chestnut-backed Antbird
  • Dot-winged Antwren
  • Short-billed Pigeon
  • White-tipped Dove
  • Long-tailed Hummingbird
  • Purple-crowned Fairy
  • Rufous-tailed Hummingbird
  • Stripe-throated Hermit
  • Violet-crowned Woodnymph
  • Chestnut-mandibled Toucan
  • Plain Xenops
  • Streak-headed Woodcreeper
  • Bright-rumped Atilla
  • Golden-crowned Spadebill
  • Great Kiskadee
  • Southern Beardless Tyrannulet
  • Tropical Kingbird
  • Masked Tityra
  • Rufous Piha
  • Bananaquit
  • Blue Dacnis
  • Cherrie’s Tanager
  • Golden-hooded Tanager
  • Gray-headed Tanager
  • Black and White Warbler
  • Mourning Warbler
  • Tennessee Warbler
  • House Wren
  • Riverside Wren
  • Great Tinamou
  • Black-throated Trogon
  • Black Vulture
  • Turkey Vulture


  • Barred Ameiva
  • Four-lined Ameiva
  • Golfo Dulce Anolis
  • Central American Smooth Gecko
  • Clawless Gecko
  • Mediterranean House Gecko
  • Brown Blunt-headed Snake
  • Cat-eyed Snake


  • Marine Toad
  • Parachuting Red-eyed Green Tree Frog
  • Red-eyed Green Tree Frog
  • Banana Frog
  • Masked Smilisca
  • Smokey Jungle Frog
  • Black and Green Poison Arrow Frog
  • Fitzinger’s Rain Frog
  • Tink Frog


  • Anartia fatima
  • Anartia jatropha
  • Glutophrissa Drusilla
  • Heliconius erato
  • Heliconius ismenius
  • Heliconius sapho
  • Heraclides cresphontes
  • Hermeuptychia hermes
  • Morpho menelaus
  • Opsiphanes tamarindi
  • Phoebis sennae


  • Bamboo Orchid Flowering
  • Black Alligator Tree Fruiting
  • Calabash flowering and fruiting
  • Cannonball Tree Flowering
  • Clusia Vine Fruiting
  • Dinner on a Plate Fruiting
  • Monkey Comb Tree Flowering
  • Candlestick Plant Flowering
  • Figs Fruiting
  • Golden Trumpet Vine Flowering
  • Hog Plum Fruiting
  • Jacaranda Flowers and Fruit
  • Ox Eye Vine Flowers
  • Protium Fruits
  • Santa Maria Flowering and Fruiting
  • Water Hyacinth Flowering
  • Yayito Fruiting

2 responses to “Flocking to a Disco Fight

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  1. Very interesting post Philip. I love the bat photos. I will need to look harder to find them myself during our next visit.


  2. Enjoyed the section on bats. Nice photos! I’m looking forward to your book.


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