Montag, 5. Februar 2018

The boundaries of the Western Palearctic and the Greater Western Palearctic

Many birders like to keep lists. Some have a list for anything. There's the basic stuff, like county, national, world or year lists, there's the more unusual stuff, like pee, touch or even eat lists. One of these lists, that many birders in Europe, Northern Africa and the Middle East keep is the Western Palearctic (WP) list. 
And even though most have a general idea of the region, there's often confusion about the regional boundaries to the WP. Maps showing the boundaries on the internet are often blurry or incomplete, therefore I created these three maps in QGIS (v2.18.15) to make for an easy visualisation.

The first map shows the usual and long-established boundaries of the WP used by most authorities and birding websites. These boundaries were defined by Cramp (1977) and published in the 'Birds of the Western Palearctic' series (BWP).*
The Western Palearctic sensu Cramp (1977).

The second map shows the new approach to define the region. The definition used for this map stems from Mitchell (2017) from 'Birds of Europe, North Africa and the Middle East. An Annotated Checklist'. A mostly similar definition will come in the 'Handbook of Western Palearctic birds' series by Shirihai and Svensson (forthcoming in 2018)
The Greater Western Palearctic sensu Mitchell (2017).
The third map compares both definitions. The 'GWP' includes all of the 'WP' plus the Arabian peninsula, Iran and some more of the Sahara.

A comparison of the two aforementioned definitions. The orange area shows what both have in common, the green color shows the additional area of the 'GWP'.
Here the definition for the Greater Western Palearctic (Mitchell 2017), with some comments:
"The northern boundary extends into the high Arctic to 82°N, to include Novaya Zemlya, all of Franz Josef Land and Svalbard, then west to 10°W and south to the Arctic Circle, so excluding Greenland but including Jan Mayen. It follows the Arctic Circle west across northern Iceland, extending north slightly to include Icelandic territorial waters (12 nautical miles from shore), then at 30°W turns south to the Azores, with a minor westward extension to include Corvo, Flores and surrounding territorial waters in that archipelago, before continuing south along 30°W. At 14°N, the boundary runs south of and thus includes the Cape Verde Islands, before heading north at 20°W and then east again at 19°N to the Mauritanian coast. To the north, the islands of the Banc D'Arguin fall within the region but the adjacent mainland coast does not, the boundary lying on the low tide midpoint between the two. From the Mauritanian coast, the boundary runs inland east at 20°N through the southern Sahara to northern Chad, thereby including the Hoggar, but not the extreme south of Algeria nor the Aïr Massif in north-west Niger. Between 16° and 20°E in northern Chad the boundary runs farther south at 18°N to include the Tibesti but not the Ennedi, then east at 20°N again to the Egyptian border. The regional boundary follows this border east along 22°N as far as Gebel Elba, where at about 34°E it moves north-east, thus excluding this Sudan-administered Egyptian territory, and reaches the Red Sea at about 22°N (sic!). All of the Arabian Peninsula is included within the region, as is all of Iran. The eastern border of this region extends into the north from the Kara Sea east of Novaya Zemlya, the north-eastern tip of which represents the most easterly point of Europe, south along the Ural ridge (following administrative boundaries) to 58°30'N, thence by an arbitrary straight line to a point 50 km east of Yekaterinburg, and by another arbitrary straight line to the head waters of the Ural River south of Zlatoust., and then south along the Ural River to the Caspian Sea, the boundary continues south along a theoretical meandering line midway between the west and east shores until it meets the Iranian border with Turkmenistan to the south-east."
This definition seems exhaustive and precise at first glance and is probably much more precise than the definition by Cramp. However there is still some vagueness at some points, which I'll list below:
  • The westward extension around Corvo and Flores is not clearly defined. I suggest the following extension: 30°W 40°N -> 32°W 40°N -> 32°W 39°N -> 30°W 39°N
  • The map and the text in BENAME do not conform with each other at the Tibesti extension, as 16°E  lies slightly east of the Niger-Chadian border, which is used as a guide line in the map. I suggest to stick with the text definition.
  • It is unclear whether the boundaries follow the political boundaries or the 20°N latitude at lake Nasser, as Sudanese waters reach north of this latitude. I suggest to use the 20°N latitude.
  • There's a minor extension south of 20°N at Gebel Elba which is not accounted for in the text, but in the map in BENAME. I suggest this should be added to the definition.
  • There's a mistake in the text definition, after moving north-east along Gebel Elba. It should read "(...) reaches the Red Sea at 23°N" instead of 22°N
  • The oceanic boundaries around the Arabian peninsula are not clearly described. I suggest a meandering line between the east and west shores of the Red Sea south to ca. 43°50'E 12°30'N, then 12 nautical miles from the shore of the peninsula
  • The eastern boundary in Russia and Kazakhstan is depicted completely wrong in the map of BENAME. Neither does it follow the Ural River, nor the Ural ridge and even the dent around Yekaterinburg is depicted far to the west. 
There are three main differences between the WP and the GWP:
  • In the WP definition by Cramp the boundary along the Mauritanian coast runs north to 21°N (as opposed to 20°N) and then eastwards from there towards the Tibesti dent
  • The Arabian peninsula is largely excluded. Instead a straight line along the 28°N latitude cuts through Saudi Arabia
  • The south-eastern boundary used is not the eastern, but the western border of Iran and its neighboring countries

I hope this post can help clear most questions about the boundaries of the WP and the GWP. A commentary on the pros and cons of both defintions will soon follow.

*The boundaries in the Caspian Sea and in the ocean around Kuwait aren't clearly defined in BWP. I therefore assumed borders that are in fact non-existent. Furthermore the lines drawn in these regions aren't exact as drawing them would be a pain in the *** without any reference line I can follow. Sorry for that)

Kommentare:

  1. Good blog and nice to see someone taking an interest in this issue. I wonder have you had a chance to look at this article from Science magazine in 2013? http://science.sciencemag.org/content/339/6115/74.full Including he Saharan-Arabian region in the "WP" simplifies the southern and SE boundaries more or less along the lines of the "GWP" proposition. But what about the NW boundary?? In fact from our experience as birders in W Europe of birds from Greenland and the NE Canadian Arctic and their migrations through our region maybe we should not be surprised by this proposition.

    AntwortenLöschen
  2. I'm looking for a shapefile of the Western Palearctic boundary to use in QGIS. Could you please email me the boundary you have used? My email is rossahmed@gmail.com

    AntwortenLöschen
  3. Great maps, and nicely written article. I've used a map and linked here from https://bubo.org/Western-Palearctic/. Hope that is fine with you.

    AntwortenLöschen