Sunday, February 28, 2010

Manitoba Breeding Bird Atlas

Some of you have asked me why my rate of posting has slowed down. Well, it is mostly because I am so busy with the Manitoba Breeding Bird Atlas - an exciting new citizen science project to document the distribution and abundance of all breeding bird species in Manitoba and to engage as many Manitobans an Manitoba communities in environmental monitoring as possible.

Knowing when I am onto a good thing, to that end I have started a second blog: My intent is to blog about citizen science and the engaging citizens in conservation on that blog, while I will my photo essays and such on this blog. Now, if only i could clone myself to get more of this exciting stuff done at once… So visit that blog and and tell me what you think!

Monday, February 22, 2010

Yucatán endemics

The Yucatán Peninsula is a flat limestone shelf that extends northward from Central America. This peninsula includes the three Mexican states of Yucatán, Quintana Roo and Campeche and northern Belize and northeastern Guatemala. The limestone rock formation means the soil layer is very thin and the topography is generally flat, unlike most of the rest of Mesoamerica. There are some small hills in parts of the peninsula and the Mayans use these to their advantage. In fact, they even contributed to the hilly topography of the area by seeking height in their architecture and building new pyramids atop the old. Here are two photos of the Mayan ruins as Uxmal (the letter “x” is pronounced like “sh” when used in a word of Mayan origin – though not necessarily so in recent writing conventions of the more than 20 Mayan languages that are spoken by more than 6 million people in this region today). As you can guess from the second photo, the Mayan ruins can make wonderful birding sites, especially where the forest has grown around the ruins and where there are tall fruiting trees, that maybe were once a food source for humans, that attract the birds. In some places, you can climb some of the pyramids and look straight into the canopy, giving a rare and privileged observation point of life in the tree tops.

The unique geology of the area has given rise to some different habitat types from those found elsewhere in the region and this has produced a certain amount of endemism. One of these unique habitats was in fact the very first image on my retina of the Yucatán Peninsula. As I flew southward towards Cancun, we crossed over a strip of very brown (dry) looking habitat between the coast and the greener interior, clearly visible from the plane (I always ask for a window seat!). You can see this area stands out on a google map – notice the browner strip I have marked with an ellipse.

This narrow strip is known as “coastal dune scrub”, sometimes also called “thorn forest” – although thorn forest is found in other coastal dry areas such as on the Pacific side. Despite the similarity of this habitat with thorn forests elsewhere, the geographic isolation of this dry forest from other dry forests means that quite a few of the plants are endemic. The dryness of this strip is related to precipitation levels and soil type, in particular a calcareous sand bar that differs from the limestone bedrock of most of the peninsula.

Of the bird that inhabit this dry strip, the most intriguing is the Yucatan Wren. Why, well because this species’ entire global range is confined to this narrow strip of habitat (a range map for this species matches the brown patch inside the ellipse on this map)! The Yucatan Wren is in the same genus as the Cactus Wren and almost as large and equally noisy. Their beautiful brown and white markings camouflage them nicely against the brown and white environment they live in as seen in these two photos!

The Mexican Sheartail, a small hummingbird, is another endemic of the coastal dune scrub with a very similar global range to the Yucatan Wren, mostly confined to this same coastal strip. I say mostly because there is a very small disjunct population of this species across the Gulf of Mexico in a dry area on the coast of Veracruz. In the Yucatán, the range of the Mexican Sheartail also extends slightly further east than that of Yucatan Wren.

The Zenaida Dove is not a Yucatán endemic because they occur on Caribbean islands as well as the Yucatán Peninsula. Nonetheless, where they do occur in the Yucatán is once again confined to the northern coastal strip, in particular areas with sand dunes, as shown here (first a bird feeding on the sand and then a pair perched up).

Most of the other Yucatan endemics are not as restricted as the sheartail and the wren and extend further south on the peninsula to varying degrees. One example is the Black-throated Bobwhite, also known as the Yucatan Bobwhite, whose range is most of the northern half of the Yucatán Peninsula but also has some smaller disjunct populations in Honduras, Guatemala and Belize. This species occurs in scrubby habitats that occur through the limestone shelf rather than the more forested areas. Here is a pair out crossing a road near Río de Lagartos (River of Lizards) in the coastal strip. The second shot shows their rather elegant pas-de-deux, up on tippy toes (and without the shoes!)

The Ocellated Turkey is also found throughout the peninsula; however they are extremely difficult to see anywhere, well, anywhere except Tikal in northeastern Guatemala, where they roam around at the base of the pyramids as if they own the place! The first photo show two birds while the second photo is zoomed in to show the remarkable iridescence of the feathers.

The Yucatan Jay is a Yucatán endemic that is found through most of the peninsula but is photographed here in the northern coastal area. The top bird in this photo is an adult (black bill), whereas as the bird with the yellow bill at the bottom is an immature bird. The brighter marking of the immature plumage, at least in terms of bill colour, is intriguing. It was also interesting to observe the immature bird apparently collecting nesting material. The Yucatan Jay and their close relatives (Bushy-crested Jay, Purplish-backed Jay and San Blas Jay) all have a cooperative breeding system with “helpers” assisting the parents in rearing the young. It seems likely therefore that the bill colour differences by age carry important social information about who has what role in the complex “extended family” arrangement.

The Gray-throated Chat is endemic to the region but extends slightly beyond the peninsula towards southeast Veracruz and into Guatemala. This species, however, is not found in the northern coastal scrub zone and is generally in slightly wetter but still scrubby (semi-arid to semi-humid) habitats. The first photo shows a male and then a female. This species and their sister species the Red-breasted Chat have attracted some interest of late as genetic studies have suggested that they may not be Wood-Warblers as previously thought… some have proposed they be in a family of their own!

The Yellow-lored Parrot, also know as Yucatan Parrot, is another endemic of the Yucatán Peninsula. Unfortunately, I only ever saw this species in flight…

The Yucatan Woodpecker (also known as Red-vented Woodpecker) is an endemic that occurs over most of the peninsula. Here is a different photo of this species from my previous post. The small size of this woodpecker means they can do well even in areas of the peninsula where the trees are quite small and in scrubby areas.

As I mentioned in the previous post, the yellow nasal tuft of the Yucatan Woodpecker is one of the features that separates that species from the dubius subspecies of Golden-fronted Woodpecker that occurs on the Yucatán Peninsula. Unlike, other subspecies of Golden-fronted Woodpecker, this race has no gold and a whole lot of red! Obviously the people who named this species were looking at a different subspecies at the time!

The Black Catbird is, well you guessed it, another endemic that occurs widely in scrubby habitat on the peninsula and islands off the coast. Behaviorally speaking, they are quite similar to Gray Catbird, though perhaps a little more skulking.

This next species is not an endemic but the stunningly beautiful Turquoise-browed Motmot has a fascinating disjunct distribution with a population in Central America extending from Costa Rica up to southwestern Chiapas and then a population over on the Yucatán Peninsula that is separated from the Central American birds by at least 400km. It is not clear if this disjunction is a result of these birds have recently disappeared from the intervening areas or whether it is older. Since they like forest edge a lot they seem quite at home in Mayan ruins and will use pyramids as nesting sites. Like some other motmots they will swing their tail from side to side in a jerky pendulum action, earning them the nickname “pájaro reloj” (clock bird). The magnificent tail with the exposed lower shaft and the broad "racquets" at the end is indeed pendulum like, but more colourful than any grandfather clock I have ever seen.

This next species is or isn’t an endemic depending on your taxonomy. The White-browed Wren is variously treated as a Yucatán endemic species, or a an endemic subspecies of Carolina Wren (can you see the plumage differences in this poor quality photo?).

Most of the Yucatán endemics, as you may have noted from the above descriptions are not true forest birds but rather birds of scrub habitat or at least more open forest types. Some however do not like the really dry parts of the peninsula and are therefore not found in the coastal dune strip of the northernmost and northwesternmost part of the Yucatán. The distribution map of these species is somewhat triangular in shape (following the parts of the peninsula with a little more rainfall and hence a little lusher vegetation) as shown in the map below:

One such species is the handsome Rose-throated Tanager. This is a male feeding in a fruit tree at the Mayan ruins of Cobá. This species is absent from the northwestern third of the peninsula.

The Green-backed Sparrow has a similar distribution to the Rose-throated Tanager, also being absent from the northwestern part of the peninsula; however, this species also extends further south and a little further west into the more humid forests of northern Guatemala and eastern Chiapas. This species is very similar in appearance to Olive Sparrow – if you know that species, see if you can spot the differences…

Some endemics of the Yucatán Peninsula actually have an even more eastern distribution in the sense that they are only found in the semi-humid scrub on the eastern side of the peninsula, which gets more precipitation than the thorn forest and do not spread westward in the southern part of the peninsula. A good example of this is the Yucatan Vireo, seen here using their large bill on an unsuspecting berry…

Of course there are a few more Yucatán endemics which I didn’t get satisfactory photos of , such as the Orange Oriole, but this should give you a good introduction of what makes the are unique in terms of its avifauna. I will try to post about some of the other birds of the region soon (sorry, getting very busy with the atlas).
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