Philip Davison Nature Diaries. Bosque del Cabo Rain Forest Lodge.

Today witnessed the arrival of the first of the winter migrants back home.  The Mourning Warbler, (Oporornis philadelphia), normally makes its annual re-appearance sometime in September but a female was seen today feeding amongst the frequent comings and goings of the resident tanagers.  Warblers are amongst the most numerous in terms of both individuals and species of migrants that bolster the already spectacular avian inventory for this special little country.

Many people consider migrants as northern latitude birds that fly south for the winter when in fact many of the migrants are tropical birds that have flown north for the summer.  Why would it benefit a bird to fly from an area seemingly teeming with food to a less diverse part of the world?  Well, although the tropics are indeed diverse in terms of numbers of wildlife, they may not present in such volume of numbers that may exist at higher latitudes. Northern summers see an explosion of insect life.  Breeding birds, whatever their normal diet, need more protein to promote rapid growth of chicks.  Longer daytime foraging hours and an abundance of food would make the journey north worth the effort.  There is also a high failure rate in raising of chicks in the tropics for no other reason than the presence of predators, particularly snakes, that prey upon the eggs and chicks.

Not all migrants are from the north.  We have just had the good fortune to watch the American Swallow-tailed Kites hawking for insects over the cabins at Bosque del Cabo.  These birds live in South America but make the journey north to Central America before the onset of the heavy rains.

Deceptive Behaviour of Side-striped Hairstreak, (Arawacus lincoides)

Arawacus lincoides. Lepidoptera. Lycaenidae. Theclinae. Costa Rica

Side-striped Hairstreak, (Arawacus lincoides)

When walking along the sunlit paths through a tropical forest, your attention may be caught by a little flickering motion.  There are many large gaudily colored butterflies but some of the smaller browns and hairstreaks, when given a closer look are more subtly beautiful.  The Side-striped Hairstreak is a tiny butterfly no bigger than your thumb nail.  You may be aware of a white flickering but pay it no attention.  When it lands, and invariably it will on the same perch, a closer inspection will reveal a remarkable escape artist.  The leading edge of the forewing is bowed out and the trailing edge is flatter so it looks as if the wings are on back to front.  The pattern is of large, alternating black and white arrows, all drawing your attention in the direction of the tip of the hindwing.  This in turn is expanded into a large head-like protuberance with a white mark reminiscent of an eye.  The hindwings have two tails that look like antennae.  Perched on a leaf, the Side-striped hairstreak continually moves the hind wings so the false antennae are twitching up and down.  Everything is leading you to believe that this is the head.   Most predators attack their prey in the region of the head because this is where the central nervous system is housed and if you destroy your prey’s central nervous system you will kill it very quickly.  Butterflies are generally the short lived winged dispersal and reproductive stage in the organism’s life history.  If a bird or a lizard takes a peck or a bite at the false head, the butterfly is only going to lose a little piece of wing membrane, fly off and live to reproduce later.  The illusion is completed by the fact that the butterfly, once it lands, walks backwards, giving every indication that the back is the front.

The Gossamer-winged butterflies or lycaenids are a very diverse family comprising about 30% of all known butterfly species.  They are also very small and many of them differ with only the slightest of color tone or markings.  I do, however, find them intriguing.  They might be small but once you get a close view of them they have a more subtle beauty that can easily be overlooked when seen from a distance.

Calycopis drusilla. Lepidoptera. Lycaenidae. Theclinae. Osa Peninsula. Costa Rica.

Drusilla Groundstreak, (Calycopis drusilla)

Philip Davison Is a Biologist, Writer and Photographer Based in Costa Rica

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: