Roberto Carmona

Red Knots Calidris canutus roselaari occur along the Pacific coast of the Americas and may use as few as four
stopover or staging sites during spring migration. There are key information gaps regarding this population’s
status and non-breeding distribution because of its localized distribution during migration, relatively small
population size (estimated population of 17,000) and a poor understanding of the location of major overwintering
sites. Based on resightings of marked birds, we assessed migratory connectivity of Red Knots along the Pacific
coast. Knots captured and marked at two sites in NW Mexico have been observed at several locations, including
migration areas in coastal Washington and the Yukon-Kuskokwim Delta in W Alaska and breeding areas in
NW Alaska. The greatest connectivity was between Guerrero Negro/Ojo de Liebre and Golfo de Santa Clara,
Mexico, and during northbound migration, between those two sites and coastal Washington, USA. Much less
is known about the southbound migration; comparatively few marked knots have been resighted north of
Mexico during autumn. We reviewed scientific literature and consulted eBird data to compile observational
records of Red Knots along the Pacific coast. Records from mainland NW Mexico document substantial aggregations
(hundreds or thousands) of Red Knots at several locations during the non-breeding season. Connectivity
involving locations in mainland NW Mexico may be demonstrated with more field effort. Additional
records along the Pacific coast south of Mexico, which involved far fewer birds, extended to extreme southern
Chile near the documented winter range of the rufa subspecies. The available information suggests the
possibility of an area of overlap in the non-breeding range of roselaari and rufa in southern Mexico; the southernmost
distribution of roselaari remains incompletely known. Comprehensive conservation assessments will
require additional investigation to identify important stopover and overwintering sites.

The Upper Gulf of California has recently been discovered as a summering area and as an important stagingarea during spring migration for the Pacific Red Knot
Calidris canutus roselaari
. In this paper we describethe feeding ecology of Red Knots using the beaches near Golfo de Santa Clara, Sonora, Mexico. DuringMarch–September 2010, we determined the abundance of knots, their abdominal profiles, agonistic relation-ships and the composition of benthic prey. The area includes two habitat types: muddy beach (in the north)and sandy beach (in the south). The highest numbers of knots were found on the sandy beach duringMarch–April 2010, with a maximum count of 842 on 24 March. Bivalves were the most abundant potential prey on both beaches. However, in spring, high densities of eggs of Gulf grunion
Leuresthes sardina
occurredon the sandy beach, attracting shorebirds. Before the spawning of Gulf grunion eggs, no aggressive encounters between birds were observed; however, after the eggs appeared intra- and interspecific agonistic behavior  became common (up 0.12 attacks/minute). In March we found mostly lean birds with low abdominal profiles,in April–May, birds became more robust (presumably mostly adults on migration to their breeding areas),and in summer and autumn birds had intermediate profiles (presumably oversummering juveniles, or juvenilesand adults that had just arrived in the area). Our results suggest that Gulf grunion eggs are the most importantfood source during spring migration, of comparable ecological importance to horseshoe crab
Limulus polyphemus
eggs in Delaware Bay, USA. The distribution of eggs led to aggressive behavior, neverthelessthe body mass of the birds increased to prepare for northward migration.

In Mexico there have been few efforts to develop monitoring programs to systematically track changes inshorebird populations. Therefore the object of this study was to develop and validate a methodology toimplement such a program for any wintering site. This was developed using shorebird count data from oneof Mexico’s most important shorebird wintering sites, the Guerrero Negro Wetland Complex. We carried out monthly shorebird counts at Guerrero Negro between July 2006 and June 2007 to identifythe sites where the greatest numbers occurred. For this purpose, we divided the study area into 45 zones, based on the type of substrate (mud, sand, dunes and marshes) and origin (natural and artificial). We selected24 of the zones (based on abundance and geographic relevance) in which 73% of the aggregate number of shorebirds was counted. We found that the abundance of shorebirds in these zones allowed us to predict thetotal abundance of shorebirds in the whole 45 zones with 98% confidence. If only the 24 zones had beencounted there would have been a reduction in effort of about 53%. A validation exercise undertaken in a portion of the lagoon complex allowed us to conclude that the monitoring model proposed predicts abundancewith 95% confidence. Important wintering sites such as Guerrero Negro are key for developing monitoring programs becausethey allow sampling trials at different scales. It is also valuable to focus studies on such sites because theycan support large proportions of biogeographic populations; e.g. Guerrero Negro hosts >30% of the populationof three shorebird species or subspecies. The methodology we propose is for the establishment of a common shorebird monitoring plan for winteringsites in Mexico, Central and South America that is simple to perform, reliable and efficient. Applying thesame method will allow the integration of shorebird monitoring efforts at regional, national and internationalscales in a way that will greatly improve our ability to determine shorebirds population trends.

En  el  complejo  lagunar  Guerrero  Negro-Ojo  de Liebre-Exportadora de Sal inverna el 31% de la población de Ganso de collar (Branta bernicla nigricans) que utiliza México  (31 000 aves en promedio). Nosotros  realizamos censos de punto mensuales (noviembre 2006 a abril 2007) en tres sitios para determinar: (1) los efectos de la época del año y del sitio en la estructura poblacional (grupos de edad) y (2) la relación del nivel de marea con la abundan- cia y la proporción de aves alimentándose. La proporción general de adultos fue de 0.68. Esta proporción fue mayor en invierno que en primavera. Por sitio en LGN y ESSA disminuyó y en LOL se mantuvo constante. El incremento de  aves  inmaduras  entre  el  invierno  y  la  primavera  se relaciona con su partida primaveral tardía. La alimentación del Ganso de collar en LOL (el sitio de mayor abundancia) fue  independiente del nivel de marea, lo que se  puede relacionar con dos conductas: (1) que las aves se muevan a lo largo de la laguna, para aprovechar el desfase, de hasta cuatro horas en el nivel de marea o (2) que modifiquen sus estrategias de alimentación, para consumir el pasto flotante.

La mayoría de las aves playeras migratorias hacen uso de los humedales principalmente como zonas de alimentación; estos sitios están sujetos a diversas amenazas debido a que en ellos convergen varios intereses humanos. El noroeste de México es una región que presenta gran abundancia de aves playeras y forma parte del corredor migratorio del Pacífico; sin embargo, aún no se cuenta con información sistemática que proporcione las bases para identificar y priorizar los hábitats aptos para la alimentación de estas aves y que brinde herramientas para desarrollar estrategias de manejo. Debido a la extensión y complejidad de estos hábitats, las imágenes de satélite son una herramienta útil para ubicarlos y caracterizarlos. En este trabajo, describimos un marco metodológico para desarrollar modelos espaciales como herramienta para identificar humedales potenciales para la alimentación de aves playeras migratorias mediante el análisis de imágenes satelitales Landsat TM, sistemas de información geográfica y métricas de paisaje. Nuestros resultados muestran diferencias consistentes en la configuración espacial de los sitios identificados en la Península de Baja California y el macizo continental. Asimismo, muestran que los sitios continentales presentan una mayor conectividad y extensión, mientras que los sitios peninsulares presentan menor extensión y mayor aislamiento. Discutimos que los aspectos que contribuyen al grado de importancia de un sitio como zona de alimentación para estas aves son su extensión, el grado de agrupamiento de los parches de sustrato húmedo dentro en cada zona y la distancia entre zonas.

Marbled Godwits (Limosa fedoa) do not present obvious sexual dimorphism, although females are known to be slightly larger than males, on average. During the nonbreeding seasons between August 2007 and April 2009, a noninvasive technique was tested that might permit phenotypic identification of sex in a large sample of individuals from the most important wintering area, Guerrero Negro, México. Blood samples (n = 577) were used for molecular sexing. For phenotypic sexing, culmen length was selected because it had the greatest sexual dimorphism. A normal distribution curve for culmen length of each sex and the overlapping area between the two curves was calculated and used to minimize the probability of error in identifying the sex of each individual. Using the criterion that males had a culmen length ≤ 106 mm and females ≥ 108 mm, the sex of 96.4% of the individuals would be correctly identified, 2.8% would be regarded as indeterminate and 0.8% would be sexed erroneously. A discriminant analysis using bill length and other commonly used phenotypic measurements did not improve success in predicting sex. The results indicate that culmen length is a useful measure for sex determination in Marbled Godwit. Identification of the sex of Marbled Godwits in the field offers new possibilities to study life histories of both sexes. In Guerrero Negro, the sex ratio of Marbled Godwits was heavily male-biased biased (2:1), suggesting latitudinal segregation by sex.

Baja California Peninsula has several wetlands that represent important ecosystems
for shorebirds. San Ignacio Lagoon is one of these sites, and supports 10% of the total abundance of shorebirds
reported in this Peninsula. Since there is few information about this group in this area, we studied spatial and
temporal changes in abundance and distribution of shorebirds in San Ignacio Lagoon. For this, we conducted
twelve monthly censuses (October 2007-September 2008) on the entire internal perimeter of the lagoon, which
we divided into four areas: two at the North and two at the South. We observed a seasonal pattern, with the
lowest abundance in May (1 585 birds) and the highest in October (47 410). The most abundant species were
Marbled Godwits (Limosa fedoa; 55% of the total records), Western Sandpipers (Calidris mauri; 23%), and
Willet (Tringa semipalmata; 10%). All three species were more abundant in autumn; for both, the Marbled
Godwit and Willet, we observed their highest numbers in winter and spring, while the Western Sandpiper
showed noticeable oscillations, reaching a maximum in early winter (December). In summer, Marbled Godwit
and Willet were the only birds present but in lower numbers. Here present the first records of the Pacific Red
Knot (Calidris canutus roselaari) in the area. Bird abundance and species richness were influenced seasonally
by migration and spatially by sites in the lagoon. The greatest shorebird abundance was in the South area of the
lagoon, probably because of better accessibility to food. Our results allowed the inclusion of San Ignacio Lagoon
in the Western Hemisphere Shorebirds Reserve Network (WHSRN) as a site of international importance.

Many shorebirds exhibit within- and among-year site fidelity during their annual cycle. Little is known, however, about the migration ecology of Red Knots (Calidris canutus) that migrate along the Pacific Flyway and occur in Washington in numbers that exceed counts elsewhere on the flyway. At two large estuaries in coastal Washington, Grays Harbor and Willapa Bay, we searched for and recorded the locations of Red Knots (N= 547) that had been individually marked with leg flags at their wintering grounds in Baja California Sur, Mexico, during the period from October 2006 to April 2009. In 2010, we resighted 43 Red Knots at Grays Harbor and Willapa Bay that had been observed at these sites in previous years, primarily in 2009. We found a high degree of site fidelity between years, with birds observed in 2010 more likely to return to the same stopover site used in 2009 than to switch stopover sites. For knots that did not switch estuaries between years, the median nearest distance between locations where individuals were observed between years was 1.4 km at Grays Harbor and 0.6 km at Willapa Bay. Our results provide the first evidence of stopover site fidelity by Red Knots of the roselaari subspecies. Fidelity occurred at three spatial scales: coastal Washington, the two estuaries where we conducted our study, and specific mudflat areas within the estuaries. Because our study sites support high populations of bivalves, Red Knots may be returning to the same areas in subsequent years to exploit what we suspect is a predictable food resource. The abundance of Red Knots and high degree of site fidelity suggest that our study sites in Grays Harbor and Willapa Bay are important for the conservation of this species on the Pacific Flyway.

Understanding the population dynamics of migratory animals and predicting the consequences of environmental change requires knowing how populations are spatially connected between different periods of the annual cycle. We used stable isotopes to examine patterns of migratory connectivity across the range of the western sandpiper Calidris mauri. First, we developed a winter isotope basemap from stable-hydrogen (δD), -carbon (δ13C), and -nitrogen (δ15N) isotopes of feathers grown in wintering areas. δD and δ15N values from wintering individuals varied with the latitude and longitude of capture location, while δ13C varied with longitude only. We then tested the ability of the basemap to assign known-origin individuals. Sixty percent of wintering individuals were correctly assigned to their region of origin out of seven possible regions. Finally, we estimated the winter origins of breeding and migrant individuals and compared the resulting empirical distribution against the distribution that would be expected based on patterns of winter relative abundance. For breeding birds, the distribution of winter origins differed from expected only among males in the Yukon-Kuskokwim (Y-K) Delta and Nome, Alaska. Males in the Y-K Delta originated overwhelmingly from western Mexico, while in Nome, there were fewer males from western North America and more from the Baja Peninsula than expected. An unexpectedly high proportion of migrants captured at a stopover site in the interior United States originated from eastern and southern wintering areas, while none originated from western North America. In general, we document substantial mixing between the breeding and wintering populations of both sexes, which will buffer the global population of western sandpipers from the effects of local habitat loss on both breeding and wintering grounds.

We describe the migratory pattern of black terns (Chlidonias niger) in the Ojo de Liebre-Guerrero Negro coastal-lagoon complex and Guerrero Negro saltworks on the Pacific coast of Baja California Sur, Mexico. Most black terns (97% of total) were seen July–October, with 6,700 birds being the highest count per month (September). During spring, this species was observed only in April (220 individuals). We recorded 90% of black terns in the southeastern portion of Ojo de Liebre Lagoon, where they were in artificial (saltworks) and natural habitats (marsh and sandy shallows). In late summer (July–August), 94% were in the lagoon, by contrast, in autumn we recorded 96% in saltworks. Overall, black terns are a common transient in Guerrero Negro during summer and autumn and uncommon during spring. Black terns use these artificial and natural habitats as stopover areas during migration.

We studied the seasonal abundance of shorebirds at the Guerrero Negro wetland complex, Baja California
Sur, Mexico, by carrying out twelve monthly censuses between July 2006 and June 2007. Total abundance
ranged from 18,000 birds in June to 370,000 in December. Shorebirds were most abundant in the Ojo de Liebre
Lagoon (peak count: 250,000 birds), followed by the Guerrero Negro Lagoon (95,000) and the man-made wetlands
created by the Guerrero Negro saltworks (83,000). The most abundant species were Western Sandpiper
Calidris mauri (41% of all observations), Marbled Godwit Limosa fedoa (27%) and Short-billed Dowitcher
Limnodromus griseus caurinus (11%).
The lagoon complex supports >1% of the flyway population of ten shorebird species and is particularly
important for Marbled Godwit (about half the world population), Red Knot Calidris canutus (32–64% of the
roselaari subspecies population) and Short-billed Dowitcher (69% of the caurinus subspecies population). The
area is also an important wintering site for Long-billed Curlew Numenius americanus, Snowy Plover Charadrius
alexandrinus and Dunlin Calidris alpina. All of these populations are identified in the U.S. Shorebird Conservation
Plan (2001) as of conservation concern.
We identified five patterns of seasonal abundance. Almost all species were most abundant in winter, were
absent or only occurred in low numbers in summer and varied in spring and autumn. Red-necked Phalarope
Phalaropus lobatus, which only occurred in substantial numbers in autumn, stood out as an exception.

Se llevó a cabo la compilación y revisión de trabajos relacionados con aves playeras (Charadrii)
realizados en México entre 1895 y 2010. Regularmente se ha manejado (e implícitamente aceptado) que
existen pocas investigaciones, sin embargo, a lo largo de este ejercicio se recabaron 221 trabajos. El 77% de
ellos fueron publicados en los últimos 20 años. Hasta la década de 1970’s la producción estuvo a cargo de
investigadores extranjeros, pero a partir de 1990 predominaron los autores nacionales. Entre artículos (160) y
tesis (30) se alcanzó el 86% del total. Sólo cuatro autores han publicado más de 10 trabajos en esta línea, lo que
indica la falta de consolidación de los grupos de investigación. El 66% de las publicaciones son descriptivas.
La especie más estudiada (20 trabajos) es el Playerito occidental (Calidris mauri). Por último, el 70% de las
investigaciones (149) se han llevado a cabo en el noroeste, de éstas, 104 se han realizado en la Península
de Baja California, donde existen los grupos de investigación más consolidados. La mayor parte de estas
publicaciones están disponibles en la biblioteca virtual de Pronatura noroeste (http://www.pronatura-noroeste.
org/). Aunque esta compilación no pretende ser exhaustiva, consideramos que las tendencias aquí mostradas
difícilmente serán modificadas. Queda de manifiesto que la parte descriptiva está prácticamente terminada en
la zona noroeste, en la cual las investigaciones se han enfocado a temas más experimentales. Sin embargo,
en el resto del país se hace necesario realizar los trabajos descriptivos básicos.

We studied a nesting colony of the Least Tern in the saltworks at
Guerrero Negro, Baja California Sur, between 31 May and 23 July 2005. We marked
the nests as they appeared and counted nests, eggs, and chicks daily. In a comparison
of two periods of laying (31 May–13 June and 17 June–19 July) average clutch size
of 15 nests (2.06 and 2.00 eggs/nest, respectively) did not differ, suggesting that in
the year of our study food was not a limiting resource. We observed 36 chicks, 31
from the fi rst period and fi ve from the second. Incubation in the second period was
interrupted by natural predation of nine nests (eight by coyotes and one by ravens).
The hatching and fl edging success of eggs laid during the fi rst period were 100%,
higher than for those laid in the second period (16% and 26%, respectively); the low
values of the second period are attributable to a longer time during which the colony
was exposed to predation. Though in an artifi cial habitat, the colony was not affected
by human disturbance and enjoyed a high success rate overall. The problem of coyote
depredation could be prevented with a fence, increasing the terns’ success further.

We report the occurrence of Red Knots Calidris canutus on the north-east coast of the Gulf of California,
Mexico. Monthly counts were conducted from Jan 2006 to Dec 2008 along a muddy beach at Golfo de Santa
Clara, Sonora. An aggregate total of 10,565 Red Knots were recorded, with a maximum count of 1,928 on
25 June 2007. Substantial numbers of over-summering birds occurred consistently in Jun–Jul with varying
numbers in Aug, but virtually none from Sep to Dec. Occasional flocks were recorded in Jan–Feb and there
was evidence of a small passage in Mar–Apr, but virtually none in May. Thus it seems that the area is used as
a stopover in early autumn and spring and that small numbers occur in winter, but its main importance is an
over-summering site for immatures that do not go to the breeding grounds. To date no other site has been found
to support significant numbers of over-summering Red Knots in the East Pacific flyway.

In recent years, more than 130 extinctions have been estimated to have occurred in the marine realm. Here we review this body of evidence and show that this figure may actually be overestimated by as much as 50%. We argue that previous estimates have not fully taken into account critical uncertainties such as naturally variable geographical distributions, and have misinterpreted documentary evidence. However, current evidence indicates that some sharks, rays and reef-associated species, although not necessarily geographically restricted, are particularly vulnerable to anthropogenic impacts and now occur in very low numbers. Overestimating extinctions is of concern because it could reduce confidence in the credibility of the ‘extinct’ category in threatened species lists and, ultimately, be used to question the integrity of conservation and management policies. We suggest that when integrating future checklists of marine extinct species, there needs to be a more rigorous use of the terminology of extinction, and participation by specialists in each of the particular taxonomic groups involved.

Distribution of aquatic birds in oxidation lagoons of La Paz city in South Baja California, Mexico. Taxonomic composition, spatial and temporal distribution of aquatic birds in oxidation lagoons (LO) of La Paz city in south Baja California, Mexico, were determined during 24 censuses realized in two-week intervals (April/98-March/99). There are five lagoons of 5 Ha each and 17 ha of terrains constantly flooded that serve as feeding areas for cattle and birds. One hundred twenty three species were observed, 75 of which were aquatic birds. A total of 46 041 observations were made (average 1 918 birds/census). Richness and abundance of aquatic birds were influenced mainly by migration of anatids and sandpipers. The first group had the greatest abundance due to its affinity towards fresh water bodies. The terrains were the favorite sites of dabbling ducks (Anas) and sandpipers. In contrast, two of the most abundant species (Oxyura jamaicensis, 12.5 % of all species, and Fulica americana, 8.8 %) restricted their presence to the oxidation lagoons. LO presented a bird structure of its own and atypical, according to the dryness of the region.

Se evaluó el efecto del nivel del mar sobre la abundancia de aves playeras en dos ambientes,
uno marino y otro dulceacuícola artificial, la playa de Chametla y las lagunas de oxidación, respectivamente,
en dos épocas del año (otoño e invierno). Las zonas de estudio son adyacentes y se localizan en la Ensenada
de La Paz, Baja California Sur, México. Se realizaron 41 censos simultáneos en los dos ambientes,
entre Octubre de 1998 y Febrero de 1999. Se observaron tres tipos de comportamiento: (1) especies exclusivas
de ambientes marinos, (2) especies que únicamente utilizaron la zona dulceacuícola, y (3) especies, al
parecer más generalistas, que pueden utilizar ambos ambientes. Para las aves generalistas, particularmente
para el Playerito Occidental (Calidris mauri), se observó un mayor uso de las lagunas de oxidación en otoño,
y de la playa de Chametla en invierno, lo cual se relaciona con la mayor demanda energética de estas especies
durante la época de movimientos migratorios. Es decir, durante el otoño, estas especies se alimentan
en Chametla durante las mareas bajas, y en las lagunas en marea alta. En general, para las especies generalistas,
los modelos exponenciales se ajustaron mejor para las lagunas en otoño, y para la playa de Chametla
en invierno, logrando explicar hasta un 60% de la variación observada.