Saturday, 19 April 2014

An Update of Birding Activity- Part 1 by Dr John L Webster

This episode was the first in a three part series titled “An Update of Birding Activity for the First 12 weeks of 2014 in Barbados”. In this series I sought to investigate and share some of the activities of both our Resident and Migratory bird species on the island, during the first 3 months of 2014. In this episode I discussed and demonstrated the changes that I observed in the moult of a male Juvenile (?) Northern Pintail duck (Anas acuta), shared the story of a juvenile American Golden Plover (Pluvialis dominica) that seemed to have taken up residence at the Grantley Adams International Airport, and shared the beauty of the Birds of the Glyricidia trees that flower annually during the first three months of the year.

This male Juvenile (?) Northern Pintail duck arrived on the island in late November. This photo was taken on 30 November 2013, Note the total absence of any of the pintail feathers for which the species is named.

Here is the same duck 3 1/2 months later, after it has completed its moult, resulting in a complete change of plumage. He is now beautiful coloured with fully developed pintail feathers, and ready to choose a mate and head back north to their breeding grounds in the Arctic tundra of Alaska and northern Canada, the Canadian prairie provinces, the Dakotas, northern Montana, northern Utah, central Nevada and the Klamath Basin of Oregon and California.

Whilst here in Barbados, the Pintail remained at a private swamp in St Philip, moving between three adjacent ponds. For the first 4-6 weeks it hung around with a small flock of Lesser Scaup ducks. In this photo it can be seen stretching its wings as it swam with the Lesser Scaup.

The Northern Pintail, highlighted here with the yellow arrow, often flew around the area with the flock of Lesser Scaup, always returning to the same ponds. When the Scaup finally moved on, the Pintail befriended a small flock of semi-domesticated Muscovy and Muscovy/Mallard cross ducks, with which it could often be seen swimming.

Here is the Northern Pintail in a fly over, clearly showing its now well developed pintail. It finally disappeared from the pond in mid-March and we assumed that it had started its annual Spring migration back to its northern breeding grounds

This Juvenile American Golden Plover arrived at Grantley Adams International Airport in late December ...somewhat late for their annual south-bound migration. It seemed to enjoy the surroundings and basically "took up residence" on and around Ramp postion 16, where the big jets park on the Eastern most side of the parking apron!. It would daily appear out on the hot paved areas, patrolling up and down, pecking at things on the tarmac and drinking from pools of rain water. When the planes arrived, it would simply walk back towards the aircraft service equipment, where it would take cover until the aircraft departed. This photo was taken during one of my patrols with the Wildlife Patrol Unit of the airport, who are given the responsibility of keeping the runway and taxiways clear of all all wildlife, including birds, to avoid birdstrikes, and the like, on aircraft. The yellow line shown in the photo, along which the bird is walking, is the line painted on the tarmac to aid the pilot in taxiing his aircraft to its parking position at Ramp Position 16 ....perhaps the Plover thinks he is also taxiing into postion!!! At the time of preparation of this show, about 3 months after the Plover made his first appearance, he was still there at the airport, keeping his daily routine ...truly an unusual bird!!

Every year during the first three months, the Glyricidia trees across the island come into flower ...a great show of beautiful pink coloured flowers. The birds go wild ...all those that feed on nectar, and also the fly catchers going behind the insects, attracted by the nectar. The trees are alive with sounds of chirping and twittering, buzzing of wings and snapping of beaks! There are constant squabbles and fights between the highly territorial hummingbirds and also with the Bananaquits. In the following photos I seek to capture some of the birds that frequent the trees and show some of their activities.

The yellow stripe above the eye indicates that this is a juvenile - in adult birds the stripe is white.

The Caribbean Elaenia, the TRUE Pee-whittler or Pee-Whistler, is one of the flycatchers that frequent the flowering trees, seeking insects.

The Grey Kingbirds, often INCORRECTLY referred to as the Pee-whittler, are always around seeking insects in flight. This one has caught a bee!

These two images are included to show the effect/importance of light on showing the iridescent colours on the throat of the hummingbirds, in this case the Green-throated Carib. They are of the same bird, taken seconds apart, with the only difference being that the bird has turned its head, thereby changing the angle at which the sunlight strikes the feathers in the neck. This area is known as the gorget. The following is a scientific explanation as to colour and iridescence seen in the feathers of Hummingbirds. It is taken from Paul A. Johnsgard's book, "The Hummingbirds of North America" (1997, second edition, published by Smithsonian Institution Press in Washington, DC.) 

The highly iridescent feathers of the hummingbird gorgets are among the most specialized of all bird feathers. But even in the male's gorget ... only about the distal third of each feather is modified for iridescence; the close overlapping of adjacent feathers thus generates the unbroken color effect. The iridescence is produced by the proximal part of the barbules, which are smooth, flattened and lack hook-like barbicels or hamuli. Beyond the color-producing portion, the barbule is strongly narrowed and curved toward the distal tip of the feather. The barbicels in this area help to hold together the barbules on the side of the barb, but do not unite the barbules of adjacent barbs. (Aldrich,1956).

...The colors do not directly depend on selective pigment absorption and reflection, as do brown and blacks produced by the melanin pigments of non-iridescent feathers. Rather, they depend on interference coloration, such as that resulting from the colors seen in an oil film or soap-bubble. Basically, the colors depend on light being passed through a substance with a different refractive index than air (1.0), and being partially reflected back again at a second interface. The percentage of light that is reflected back increases with the difference in the refractive indices of the two media; in addition, the thickness of the film through which the light is passed strongly influences the wavelengths of light that are reflected back. Put simply, red wavelengths are longer than those at the violet end of the spectrum and generally require films that are thicker or have higher refractive indices than those able to refract bluish or violet light. Thus, the optimum refractive index for red feathers is about 1.85; for blue feathers it is about 1.5.

Hummingbird feathers may attain any refractive index within this range because the iridescence portions of the barbules are densely packed with tiny, tightly packed layers of platlets. These platlets are only about 2.5 microns in length and average about 0.18 microns in thickness, but they vary in thickness and are differentially filled with air bubbles. The platlets matrix, probably of melanin, evidently has a refractive index of about 2.2, whereas the air bubbles inside have a refractive index of 1.0. Varying the amount of air in the platelets provides a composite refractive index that ranges from the red end of the spectrum (1.85) to the blue (1.5)....

Thus, the actual thickness of the platlets not only significantly determines the quality of the perceived light, but it also affects the amount of air held within the pigment granules and the consequent variations in interference effects. Further, a single pigment granule can produce different color effects according to the angle at which it is viewed. When an optical film is viewed from about, it reflects longer wavelengths than when viewed from angles progressively farther away from the perpendicular. Thus, a gorget may appear ruby red when seen with a beam of light coming from directly behind the eye, but as the angle is changed the gorget color will shift from red to blue and finally to black, as the angle of incidence increases (Greenwalt, 1960a).

In hummingbirds, the color-producing pigment platlets are closely packed into a mosaic surface, and 8 to 10 such layers are then tightly stacked on top of one another in typical iridescent feathers. Far from confusing the visual effects, such stacking actually tends to intensify and purify the resulting spectral color, which is why hummingbirds have possibly the most intensively iridescent feathers known in birds (Greenwalt, 1960a).

In late February 2014, I was invited to give a presentation on the Birds of Barbados, to a group of 56 birders, mainly from the USA, who were on a Caribbean Birding Cruise. The cruise, organised by Victor Emanuel Nature Tours of Texas, started in Antigua and sailed down the islands to Barbados, stopping at each of the islands on the way for a 1 day birding trip, The objective was to see the birds of each island, particularly those which are endemic to that island and hence not likely to be seen elsewhere. The cruise terminated in Barbados, where I delivered my presentation at the Graeme Hall Nature Sanctuary followed by a bit of birding right there on the site, Our only endemic bird species, made itself very present, thereby allowing our visitors to get up close and personal with the Barbados Bullfinch, our lowly Sparrow!. Whereas I considered it a privilege to be invited to present to such an esteemed group, the highlight of my day was to meet a true icon in the natiure tour business, Victor Emanuel, founder of Victor Emanuel Nature Tours, a gentleman with 50 years in the business!!