Ensenada de la Paz is located on the southeast coast of the Baja California Peninsula. The lands that comprise the WHSRN site are federally owned. For shorebirds migrating throughout the peninsula, Ensenada de La Paz is the last feeding ground of their southbound (fall) migration and the first of their northbound (spring) migration. In general there is little surf, making it possible for fine sediment to accumulate in the southern section of the inlet and form a floodplain where shorebirds feed. The southwest portion of the Ensenada de La Paz, known as Chametla–El Centenario salt marsh, is a floodplain strongly influenced by tides, with more than 1,000 linear meters of wetlands exposed during spring tides. The region’s climate is arid, with an average annual rainfall of 200 mm that is constantly outpaced by evaporation. The tides in this area are mixed semidiurnal. From October to March, the prevailing winds are from the northwest, and from April to September, from the southeast.
Until 2006, the site was used by at least 20,000 shorebirds throughout the year. The area also supported more than 1% of the biogeographic populations of five species: Snowy Plover (Charadrius nivosus, 1.13%), Wilson’s Plover (Charadrius wilsonia, 10.6%), Semipalmated Plover (Charadrius semipalmatus, 1.8%), Whimbrel (Numenius phaeopus, 1.01%), and Marbled Godwit (Limosa fedoa, 1.12%). To date, human pressures have resulted in close to 60% of the shorebirds not using the area. However, the percentage of the biogeographical Snow Plover population at the site continues to be above 1%. For this, Ensenada de la Paz still meets the biological criteria for being a WHSRN Site of Regional Importance.
National and International Recognitions of the Site
Ensenada de La Paz is recognized by at least four distinctions: 1) a WHSRN Site of Regional Importance; 2) Priority Wetland for Shorebirds in Mexico (No. 20); 3) a Mexican Important Bird Area (AICA, or IBA, No. 93), category G-1 (global); and 4) a Ramsar Wetland of International Importance (No. 1816).
There are several threats to the site: (1) the discharge of solid waste (plastics, rubber, tires, and general trash); (2) occasional spills of gasoline and lubricants, which have increased as urban growth has increased; (3) growth of the urban area is the most serious threat, which now includes construction adjacent to the site that uses terrigenous sediment for fill, causing degradation of the area. There are also various pressures associated with human settlements, such as (4) the presence of dogs and cats, (5) continuous foot traffic and vehicles, and (6) constant noise and lights. All of which has contributed to the reducing the quality of the site. Therefore, it is urgent to propose targeted conservation measures, such as: regulating construction in the area, controlling the presence of exotic animals (dogs, cats, etc.), preventing the discharge of solid and liquid waste, and carrying out awareness campaigns within the community.
Ecology & Conservation
The area is located on the La Paz Bay, in the extreme southeast of Baja California Penisula. With an area of approximately 2,000 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 usually 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 rocky and sandy substrates along much of its coast. Muddy substrates are found only along the extreme southern part of Ensenada de La Paz. Baja California Sur’s capital city of La Paz, with approximately 250,000 inhabitants, is situated on the banks of the lagoon. Given the city’s proximity to the bay, said population presumably impacts this body of water. The tides in this region are mixed semidiurnal; from October to March, the prevailing winds are from the northwest, and from April to September, the southeast.
The Chametla–El Centenario salt marsh is located in the southern part of 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. Given the slight elevation gradient, the level of the sea has a considerable affect on how much of the area is available to shorebirds for foraging. During low tide some 500 to 1,000 linear meters are exposed, while during high tide the water may reach the berm. The vegetation in the higher areas of the salt marsh consists of scrub and cactus, while red mangrove (Rhizophora mangle), black mangrove (Avicenia germinans), and Salicornia spp. predominate the zone bordering the sea.
Until 2006, the WHSRN site was used by at least 20,000 shorebirds annually. However, in the last few years there has been a notable decline in its use. Surveys carried out during the winter of 2011/2012 recorded 6,800 to 7,500 shorebirds in the zone (Brabata 2012), a reduction of more than 60% in the usual abundance (see Threats section).
The various species and their relative importance remain the same at the site, despite the aforementioned decreases—meaning disturbances have affected the species similarly. The most common shorebirds at the site are: Western Sandpiper (Calidris mauri, 51% of the birds observed in 2006 and 67% in 2011); Marbled Godwit (Limosa fedoa, 7.2% and 6.3%), Semipalmated Plover (Charadrius semipalmatus, 4.2% and 3.6%). Although less abundant, other common species include Black-bellied Plover (Pluvialis squatarola), Willet (Tringa semipalmata), Whimbrel (Numenius phaeopus), Least Sandpiper (Calidris minutilla), y dowitchers (Limnodromus spp.).
Further qualifying the site for its WHSRN designation in 2006 was the fact that the Chametla–El Centenario zone supported more than 1% of the biogeographic population of five shorebird species: Snowy Plover (Charadrius nivosus, 1.13%), Wilson’s Plover (Charadrius wilsonia, 10.61%), Semipalmated Plover (Charadrius semipalmatus, 1.8%), Whimbrel (Numenius phaeopus, 1.01%), and Marbled Godwit (Limosa fedoa, 1.12%). To date, this criterion only applies to Snowy Plover (1.37%, nearly the same as in 2006). Given this, Ensenada de la Paz continues to qualify as a WHSRN Site of Regional Importance, despite the drastic reduction in the number of shorebirds using the site overall.
Other relevant taxa
Least Terns (Sterna antillarum, under special protection) nest in the upper part of the Chametla–El Centenario beach area. In addition, several species of herons nest in the mangrove area including the Great Blue Heron (Ardea herodias santilucae, under special protection), Reddish Egret (Egretta rufescens, under special protection), Black-Crowned and Yellow-Crowned Night Herons (Nycticorax nycticorax and Nictanassa violacea), Little Green Heron (Butorides virescens), and White Ibis (Eudocimus albus).
Three species of plover also nest in the upper parts of the beach, although in lower numbers: Killdeer (Charadrius vociferous), Wilson’s Plover (Charadrius wilsonia), and Snowy Plover (Charadrius nivosus, considered endangered); as does American Oystercatcher (Haematopus palliates, in danger of extinction). All protection categories per Mexican Official Rule, NOM-ECOL-059.
Fortunately, the tourism mega-project that posed a major threat in 2006 within Ensenada de La Paz, particularly the Chametla–El Centenario beaches, never came to pass. However, other threats persist, such as discharge of solid waste (plastic, rubber, tires, and trash in general), and occasional spills of gasoline and lubricants that have increased as urban growth has increased. This urban growth is the principal threat at the site, especially construction adjacent to it that uses terrigenous sediment as fill, degrading the area. In some places, new construction practically borders the shorebirds’ foraging areas. Other disturbances associated with human settlements that negatively affect the site include the presence of dogs and cats, foot traffic and vehicles, and constant light and noise. The accompanying image shows two areal photos of the same portion of Ensenada de la Paz, one from 1982 (A) and the other, 2012 (B). Two differences stand out: (1) the apparent loss of the supralitoral zone, and (2) encroachment of construction, some located right alongside the mudflats.
As noted in 2006, despite Chametla–El Centenario forming part of IBA 93 (Ensenada de la Paz), with the highest category of G-1, this WHSRN site does not have a management plan. It is of utmost importance to propose targeted measures for conserving this site, such as: regulating construction, controlling the presence of feral fauna (dogs, cats, etc.), preventing the discharge of solid and liquid wastes, and carrying out public awareness campaigns in the community.
From 1992 to 2005, as part of a research program on shorebird use of this region, 14-day-long surveys were carried out regularly, as were mist-net captures. Nearly 1,000 individual Western Sandpipers (Calidris mauri) and 350 Least Sandpipers (Calidris minutilla) were banded. The information generated by these studies was published in various works, reconfirming the importance of the site for shorebirds. However, since 2005 the research effort has been notably reduced, such that between 2011 and 2012 it was limited to three surveys (two winter, one spring).
Photos by Georgina Brabata and Roberto Carmona, unless otherwise noted.
Click on each thumbnail to see a bigger picture.
Shorebirds that Breed at the Site
American Oystercatcher (Haematopus palliatus),recently listed
The site hosts both resident and migratory groups of Snowy Plover (Charadrius nivosus), recently listed in Mexico as a threatened species.
Aerial photographs of Ensenada de La Paz show the apparent loss of the supralitoral zone and urban encroachment: A = 1982, B = 2012.
Banding and resighting programs
In his doctoral thesis, R. Carmona (2007) documented his 2001–2002 field season studying Western Sandpipers (Calidris mauri) and Least Sandpipers (C. minutilla) through banding and categorizing by sex and age group. In total, 1,145 Western Sandpipers were caught, of which 388 were adult males and 401 juvenile males; 132 were adult females and 189 juvenile females; and another 16 adults and 19 juveniles were of indeterminate gender. Of the total captured, 856 were banded. For Least Sandpipers, a total of 387 were caught, of which 121 were adult males and 56 juvenile males; 78 were adults females and 40 juvenile females; and another 64 adults and 28 juveniles were of indeterminate gender.
Vázquez (2007) monitored the 856 banded Western Sandpipers during the following 2002–2003 field season to determine the species’ fidelity to and temporary use of Ensenada de La Paz. He made 1,234 resightings of 328 birds, for a return rate of 38% ; the high fidelity presumably was due to Chametla being the only wetland available in the southeastern portion of the Baja California Peninsula. Further, it offers low levels of predation and large areas for foraging. Males had higher rates of return than females. Also, first-year adult males were resighted more frequently than those 2 or more years in age, apparently due to the nomadic behavior of the older birds. The median departure date for banded birds was 28 February. Departure dates by sex and age group were the same, meaning that gender separation occurs at sites closest to the breeding grounds.
· Brabata (1995) assessed the importance of Chametla as a feeding, resting, and wintering area for the Marbled Godwit (Limosa fedoa), Willet (Tringa semipalmata), Whimbrel (Numenius phaeopus), and Long-billed Curlew (Numenius americanus), as well as its seasonal abundance and variations. She observed that these species preferentially utilized the intertidal mudflats for feeding and the mudplains (upper portion) for resting.
· Fernandez et al. (1998) surveyed Ensenada de La Paz’s Chametla beach for one year. The most abundant species was Western Sandpiper (Calidris mauri), particularly during fall migration and winter. There was no increase in the species’ abundance in the spring, suggesting a lack of connection here on the northbound migration route. There are two types of habitat at this site, marshland and mudflats; the latter being more important for foraging shorebirds.
· Brabata (2000) determined the spatial-temporal distribution of Western Sandpipers, the population structure by sex during a one-year cycle, and the relation between bird presence and type of substrate. It was found that the species is most abundant in January, and distributed primarily in the silt-sandy areas of Ensenada de La Paz. The proportion of males was greater than females in the study area by a ratio of 4:1.
· Carmona et al. (2003) recorded nine new and less-common species of shorebirds in Ensenada de La Paz. Four of these were observed in Chametla–El Centenario: the first American Golden-Plover (Pluvialis dominica) recorded for La Paz Bay; the first Terek Sandpiper (Xenus cinereus), recorded for Mexico; the second Red Knot (Calidris canutus) ever recorded for La Paz Bay; and the first Semipalmated Sandpiper (Calidris pusilla) recorded for Baja California Sur!
· Carmona et al. (2003b) evaluated the effect of tide level on shorebird abundance on Chametla beach and adjacent oxidation lagoons in the fall and winter. They observed three types of behavior: 1) exclusively marine environment species; 2) species that only utilize the freshwater zone; and 3) generalist species that utilize both environments. For the generalists, in particular Western Sandpiper (Calidris mauri), they observed a greater use of the oxidation lagoons in the fall and of the Chametla beaches in the winter, which corresponds to a greater energy demand during the migratory season.
· Galindo-Espinosa (2003) determined the utilization patterns of Western Sandpiper (Calidris mauri) in the coastal area (Chametla-El Centenario beaches) and in an artificial freshwater area (oxidation lagoons). He found that the population structure by sex had a 4:1 ratio, male to female, and the global population structure by age was 1:1, but distinct between the two wetlands: 62% of adults on the beaches and 38% in the lagoons. Western Sandpiper utilized Chametla–El Centenario beaches in the fall and winter, and the lagoons mainly in the fall.
· Galindo et al.(2004) documented Mexico’s first record of Terek Sandpiper (Xenus cinereus) on the beach in Chametla, on April 11, 2002. It was seen again at the end of May and August, and for the last time on February 10, 2003, implying that it visited the area at least two consecutive years.
· Carmona et al.(2005) described the effect of tide levels on an alternate feeding area adjacent to Chemetla beach (the oxidation lagoons of the City of La Paz) during the fall. They found a positive relationship between abundance and density and increased rates of intraspecies aggression among Western Sandpipers. The highest levels of aggression occurred during high tide due to increased density and competition. In the fall, the alternate sites become important to meeting the energy requirements of this species.
· Sauma (2006), and later Carmona and Sauma (2010), determined the abundance and population structure of Least Sandpipers (Calidris minutilla) on Chametla beach and five adjacent oxidation lagoons. They observed the greatest abundances in August and February in the lagoons and beach, respectively, indicating that birds were using the lagoons during migration and the beach during winter. Males were more abundant in the fall, and females in the winter; adults were more abundant in the fall, and juveniles in the winter. In sum, Ensenada de La Paz seems to be most utilized in the fall by adult males and in the winter by juvenile females.
· Carmona (2007) identified and assessed the population dynamics and habitat use of shorebirds in Ensenada de La Paz between 1996 and 2003. He developed a species list that places this site as the richest in the country (36 species), and compared use patterns in coastal zones and oxidation lagoons. The lagoons were most used in the fall, and the beach from the fall to early spring. This biological information supported the designation of Ensenada de la Paz as a WHSRN Site. For species occurring in both places (coastal zone and oxidation lagoons), tide level was a determining factor in their use, particularly for Western Sandpiper, the most numerous species. Composition by sex and age group for Western and Least Sandpiper populations was determined and compared in both locations. Western Sandpiper adults were more abundant on the beach (80%) in winter, and juveniles in the lagoons (80%). By gender, Least Sandpipers showed no differences between the sites; by age, adults were more abundant in the fall (80%) than in winter (30%). In analyzing the probability of capture for Western Sandpipers, gender had a low effect whereas age had a marked effect.
· Morales (2007) compared habitat quality between Chametla–Centenario beach and the oxidation lagoons for Western Sandpipers (Calidris mauri) during the 2004–2005 field season. The highest densities occurred in the lagoons in the fall, and on the beach in the winter and spring. Additionally, there was a greater use of the lagoons during periods of high tide in the fall and early winter. The proportion of females (37%) and juveniles (78%) was greater than observed in previous studies in this area. In the fall, the biomass of available food was greater in the lagoons; in winter, on the beach. A show of defense and aggression was observed more frequently in the lagoons, where there was also a greater abundance of predators. This, together with more vegetation cover, increased the risk of predation at that site. In sum, the lagoons represent an alternate but sub-optimal environment that is used by only a portion of the population during the fall.
· Brabata (2011) conducted a taxonomic literature review of aquatic and marine species found in the Bay of La Paz and found a total of 160 species recorded in the bay, of which 28 are shorebirds. Fieldwork also was conducted in three areas: Espiritu Santo Island, oxidation lagoons, and Chametla beach, where 6, 18, and 22 species of shorebirds, respectively, were observed. The beach had the highest abundances, with Western Sandpiper (Calidris mauri) being the most numerically dominant species.
· Brabata (2012) conducted three surveys in Ensenada de La Paz for a report for the Biological Monitoring Program of the National Commission on Protected Areas: the first in December 2011, the second during winter of 2011 (as part the annual Christmas Bird Count), and the third in April 2012. The surveys recorded 15, 23, and 13 species, respectively; the total number of individuals reported was 7,540, 6,781, and 1,792, respectively. The most abundant species was Western Sandpiper (Calidris mauri), representing 83%, 52%, and 69% of the population in each survey, respectively. The presence of American Oystercatcher (Haematopus palliatus) and Snowy Plover (Chraradrius nivosus), both federally protected species in Mexico, were also noted during the surveys.
Eduardo Palacios Castro
Center for Scientific Research and Higher Learning of Ensenada (CICESE), La Paz Campus
Northwest Center for Biological Research, S.C.
Natural Resources Use and Restoration Department
Secretary of the Environment and Natural Resources
Baja California Sur Delagation
Georgina Brabata Domínguez
Autonomous University of Baja California Sur
Juan Ramón Guzmán Poo
Autonomous University of Baja California Sur
Autonomous University of Baja California Sur
Mariela Amador Amao
Autonomous University of Baja California Sur
Bibliography relevant to Ensenada de la Paz WHSRN Site
Brabata, G. 1995. Presencia y conducta alimenticia de cuatro especies de playeros (Scolopacidae) en la Ensenada de La Paz, B.C.S. Tesisde Licenciatura. Depto. Biología Marina. Universidad Autónoma de Baja California Sur. 64 p.
Brabata, G. 2000. La Ensenada de La Paz, B.C.S., como parte de la ruta migratoria de Calidris mauri (Charadriiformes: Scolopacidae): su estancia a lo largo de un año. Tesis de Maestría Centro Interdisciplinario de Ciencias Marinas I.P.N. La Paz, B.C.S. México. 64p.
Brabata, G. 2011. Estructura y función de las asociaciones de aves en ambientes costeros e insulares de la Bahía de La Paz. Tesis doctoral. Posgrado en Ciencias Marinas y Costeras, Universidad Autónoma de Baja California Sur. 167 p.
Brabata, G. 2012.La Ensenada de La Paz. In: Vega, X., E. Palacios, &G. Fernández. Monitoreo de Aves Playeras migratorias en 11 sitios prioritarios del Noroeste de México, en los estados de Baja California Sur, Baja California, Sonora, Sinaloa y Nayarit. Reporte Final. Centro de Ciencias de Sinaloa para la CONANP programa PROMOBI 2012.
Carmona, R. 2007. Dinámica poblacional y uso de hábitat de las aves playeras en la Ensenada de La Paz, como componente del corredor migratorio del Pacífico. Tesis doctoral. Posgrado en Oceanografía Costera, Universidad Autónoma de Baja California. 253 p.
Carmona, R. & L. Sauma. 2010. Uso de dos ambientes, costero y dulceacuícola, por el playerito menor (Calidris minutilla) en la Península de Baja California, México. Ornitologia Neotropical. 21: 545–554.
Carmona, R., D. Galindo & L. Sauma. 2003a. New and noteworthy shorebirds records from South Baja California Peninsula, México. Wader Study Group Bull. 101/102: 62–66.
Carmona, R., A.M. Álvarez, A. Cuéllar Brito & E. M. Zamora Orozco. 2003b. Uso estacional de dos áreas, marina y dulceacuícola, por aves playeras en función al nivel de marea, en Baja California Sur, México. Ornitología Neotropical 14: 201–214.
Carmona, R., A. Franco & R. López. 2005. Niveles de agresión del Correlimos de Alaska Calidris mauri en un ambiente dulceacuícola de la Península de Baja California, México. Ardeola. 52(2): 365–369.
Fernández, G., R. Carmona & H. De La Cueva. 1998. Abundance and seasonal variation of western sandpipers (Calidris mauri) in Baja California Sur, Mexico. The Southwestern Naturalist 43(1):57–61.
Galindo, D., G. Mlodinow, R. Carmona & L. Sauma. 2004. Terek sandpiper (Xenus cinereus): a first for México. North American Birds 58: 454–455.
Galindo. D. E. 2003. Uso de dos humedales, dulceacuícola y costero, por Calidris mauri (Charadriiformes: Scolopacidae) al sur de la península de Baja California, México. Tesis de Maestría. Centro Interdisciplinario de Ciencias Marinas I.P.N. La Paz, B.C.S. México. 76 p.
Morales, K. L. 2007. Evaluación de la calidad de hábitat en un ambiente costero y uno dulceacuícola, para Calidris mauri en La Ensenada de La Paz, B.C.S., México. Tesis de Maestría. Centro Interdisciplinario de Ciencias Marinas I.P.N. La Paz, B.C.S. México. 88 p.
Sauma, L. 2006. Uso migratorio de La Ensenada de La Paz, B.C.S. México por Calidris minutilla (Aves: Charadriiformes): comparación entre un ambiente marino y uno dulceacuícola. Tesis de Licenciatura. Depto. Biología Marina. Universidad Autónoma de Baja California Sur. 57 p.
Vázquez, R. 2007. Fidelidad a la ensenada de La Paz, B.C.S. México como sitio de invernación del playerito occidental (Calidris mauri). Tesis de Licenciatura. Depto. Biología Marina. Universidad Autónoma de Baja California Sur. 54 p.