Ensenada de la Paz is located on the southeast coast of the Baja California peninsula. The site lies on federal government lands. For shorebirds migrating throughout the peninsula, Ensenada de La Paz is the last feeding ground in the southbound migration and the first in the northbound migration. In general there is little surf, thus making it possible for sediment to accumulate in the southern section of the inlet and form a flood plain where shorebirds feed. The southwest portion of the Ensenada de La Paz, known as Chametla-El Centenario salt marsh, is a flood plain strongly influenced by tides, with more than 1000 linear meters of wetlands exposed during spring tides, which makes the prime feeding site for shorebirds. The tides in this region are mixed semidiurnal; the prevailing winds are northeasterly from October to March and southeasterly from April to September.
More than 20,000 shorebirds use the Chametla-El Centenario portion of the site during the year, the Western Sandpiper (Calidris mauri) being the most abundant. In addition, more than 1% of the biogeographic populations of five species can be found here: Snowy Plover (Charadrius alexandrinus, 1.1%), Wilson’s Plover (Charadrius wilsonia, 10.6%), Semipalmated Plover (Charadrius semipalmatus, 1.8%), Whimbrel (Numenius phaeopus, 1.0%), and Marbled Godwit (Limosa fedoa, 1.1%). Also common, although in lesser numbers, are: the Willet (Catoptrophorus semipalmatus), Whimbrel (Numenius phaeopus), Least Sandpiper (Calidris minutilla), and dowitcher (Limnodromus spp.).
Ensenada de La Paz, which includes Chametla-El Centenario, is Mexican Important Bird Area (IBA) 93, placed category G-1 (global). This is the highest category that can be assigned and is due to the presence of nests of the California Least Tern (Sterna antillarum browni), a subspecies in danger of extinction.
On the other hand, financing is currently being sought for special projects dealing with the protection of nature in general and shorebirds in particular.
The area is located on the Bahia de La Paz, in the extreme southeastern region of Baja California. With an area of approximately 2000 square kilometers, this bay is the largest protected body of water on the east coast of the peninsula. The region’s climate is arid, with an average annual rainfall of 180 to 250 mm, which is constantly being exceeded by the amount of evaporation. The heaviest rains fall in September, coinciding with hurricane season. The average annual temperature is 24º C, with a low of 5º C in January and a high of 42º C in August. The bay has a rocky substrate, while the coast is sandy for the most part. It is only in the Ensenada de La Paz at the extreme southern end of the bay that we find a muddy substrate. The city of La Paz, capital of the state of Baja California Sur, with approximately 180,000 inhabitants, is situated on the banks of the lagoon. This population presumably impacts this body of water given the proximity of the city to the lagoon. The tides in this region are mixed semidiurnal; the prevailing winds are northeasterly from October to March and southeasterly from April to September.
The Chametla-El Centenario salt marsh is located in the southern part of the Ensenada de La Paz and extends some 6 kilometers. The beach is composed of a fine grained substrate with salt horizons, intercalated with clay and mud. Due to the slight gradient, the sea level greatly affects the feeding area available to shorebirds. During low tide some 500 to 1000 linear meters are exposed, while during high tide the water may reach the berm. The vegetation in the salt marsh is scrub and cactus in the higher areas; red mangrove (Rhizophora mangle), black mangrove (Avicenia germinans), and Salicornia spp. predominate in the zone bordering the sea.
At least 20,000 shorebirds use the WHSRN site annually. The most common are: the Western Sandpiper (Calidris mauri, 50.5% of the total number observed), Marbled Godwit (Limosa fedoa, 7.2%), and Semipalmated Plover (Charadrius semipalmatus, 4.2%).
The California Least Tern (Sterna antillarum browni) nests in Chametla-El Centenario in higher areas away from the shoreline. Two plovers, Wilson’s Plover (Charadrius wilsonia) and the Snowy Plover (Charadrius alexandrinus) as well as the American Oystercatcher (Haematopus palliatus) also nest there. In addition, several species of herons nest in the mangrove area including the Great Blue Heron (Ardea Herodias), Reddish Egret (Egretta rufescens), Black-Crowned and Yellow-Crowned Night Herons (Nycticorax nycticorax and Nictanassa violacea), Little Green Heron (Butorides virescens), and White Ibis (Eudocimus albus).
Possible threats are: (1) a tourism mega-project within Ensenada de La Paz, facing the Chametla-El Centenario beaches, that will most likely cause disturbances during construction as well as changes in water current and sediment patterns due to dock construction; (2) solid waste discharges (plastic, rubber, tires, etc.) and occasional gasoline and lubricant spills that, although currently moderate, could become a serious problem as the population grows; (3) possible future construction degrading the site due to necessary depositing of terrigenous sediment fill, as seen in similar projects already built in other parts of the lagoon., such as the Fidepaz Marina.
In spite of the fact that Chametla-El Centenario forms part of IBA 93 (Ensenada de la Paz), classified as G-1, the site does not have a management plan at present. Crude shrimp cultivation ponds were constructed above the intertidal zone. These ponds were abandoned a little less than ten years ago and are currently being used as an additional habitat by modest numbers of shorebirds. There have been regular field trips into the zones (semi-monthly censuses) from 1992 to the present to survey shorebird in the area. Additionally, shorebirds have been captured, most commonly two species, the Western Sandpiper (Calidris mauri) and Least Sandpiper (Calidris minutilla). Various papers have been written underscoring the importance of the site for shorebirds. An annotated list of the most representative works follows:
Carmona et al. (2003) recorded nine new and rare shorebirds in Ensenada de La Paz. Four of these were observed in Chametla-El Centenario: the American Golden Plover (Pluvialis dominica), the first recorded for the Bahía de La Paz; the Terek Sandpiper (Xenus cinereus), the first recorded for Mexico; the Red Knot (Calidris canutus), the second recorded for the Bahía de La Paz; and the Semipalmated Sandpiper (Calidris pusilla), the first recorded for Baja California Sur.
Brabata (1995) assessed the importance of Chametla as a feeding, resting, and wintering area for the Marbled Godwit (Limosa fedoa), Willet (Catoptrophorus semipalmatus), Whimbrel (Numenius phaeopus), and Long-billed Curlew (Numenius Americanus), as well as for its abundant resources and seasonal variations. She observed that these species preferentially utilized the intertidal mudflats for feeding and the brackish flats (upper portion) for resting. Fernández et al. (1998) drew similar conclusions for the Western Sandpiper (Calidris mauri), the most abundant species in the zone.
Galindo-Espinosa (2003) assessed the utilization patterns of the Western Sandpiper (Calidris mauri) in the coastal area (Chametla-El Centenario beaches) and in an artificial freshwater area (the oxidation pools). He found that the population structure by sex had a 4:1 male to female ratio as opposed to the global ratio of 1:1. However the beach contained 80% adults and the pools 80% juveniles. The Western Sandpiper (Calidris mauri) utilized Chametla-El Centenario in the autumn and winter, while in contrast they utilized the pools mainly in the autumn.
Carmona et al. (2003) evaluated the effect of tide level on shorebird abundance on Chametla beach and the oxidation pools in the autumn and winter. They observed the behavior of three types of species: 1) exclusively marine environment species, 2) species that only utilize the freshwater zone and 3) generalist species who utilize both environments. For the generalists, in particular the Western Sandpiper (Calidris mauri), they observed a greater use of the oxidation pools in the autumn, and of Chametla beach in the winter, which corresponds to a greater energy demand during the migratory season.
Recently, Vázquez (under review) determined a general rate of return for the Western Sandpiper (Calidris mauri) of 56%, with a greater proportion (65%) being males, compared with the females (40%); by age there were no differences among first year adults and second year adults and older.
Photos by Georgina Brabata and Roberto Carmona
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M. en C. Roberto Carmona
Director del Laboratorio de Aves
Universidad Autónoma de Baja California Sur
Carretera al Sur Km 5.5.
La Paz, Baja California Sur, CP 23000
M. en C. Georgina Barbata
Departamento de Biología Marina
Universidad Autónoma de Baja California Sur
Carretera al Sur km 5.5. C.P. 23080
A.P. 19-B. La Paz, B.C.S. México
Tel. (612) 12 3 88 00 ext. 4180, 4100, 4005
Fax. (612)12 3 88 19 ext. 4099
Adriana del Moral
Delegado Federal, SEMARNAT
Avenida Ocampo #1045 Col. Centro
La Paz, Baja California Sur, CP 23000
Tel: (01612) 123 93 07