We present 9 recent records of rare waterfowls in Baja California Sur, all of them in artificial wetlands:3 freshwater sites and 1 concentration area for a saltworks. We present the first records of the Ross’s Goose in thestate. The remaining 8 species are: Black-bellied Whistling-Duck (breeding), Fulvous Whistling-Duck, Greater WhitefrontedGoose, Snow Goose, Cackling Goose, Tundra Swan, Mallard and Hooded Merganser. To this list we addedan historical compilation of the records of these species in artificial sites of the state. The artificial wetlands are noreplacement for their natural counterparts, they are nevertheless an important part of the region’s landscape mosaic. Asthe records of the present work exemplify, this man-made habitat increases the regional species richness, and should beconsidered as important areas that need to be protected.

El Playerito occidental (Calidris mauri) es el ave playera más abundante en el corredor migratorio del Pacífico. Esta especie ha sido estudiada en diferentes puntos de la Península de Baja California y la costa de Sinaloa. Sin embargo, no se han realizado trabajos en sitios más sureños, como Marismas Nacionales (MN). En el estudio presente determinamos la distribución espacio temporal de la especie en MN (septiembre 2013-marzo 2014), mediante conteos mensuales. MN fue utilizada por al menos 30,000 individuos, el sitio más relevante fue laguna El Chumbeño (57% de registros totales). Las aves arribaron a MN en octubre, tres meses después que en otros sitios del noroeste mexicano, esto en relación con el elevado nivel de agua ocasionado por las lluvias inmediatas anteriores. Se presentó una relación positiva entre la abundancia de la especie de interés en los sitios con la superficie húmeda, y negativa con el área cubierta por vegetación. Las abundancias mayores se presentaron de octubre a enero y descendieron a partir de febrero, dada la migración primaveral y la desecación de sitios de alimentación.

Evaluamos la importancia numérica de las lagunas costeras sonorenses para la invernada de aves playeras, a través de recorridos aéreos en las 13 lagunas de mayor tamaño durante febrero de 2017. Realizamos en total 400,716 registros, el 70% de éstos se llevaron a cabo en la porción sur, el 9% en el centro y el 21% al norte del estado. Las tres bahías con mayores números y porcentajes de aves playeras fueron Tóbari (127,570 registros, 32%), Yavaros-Moroncarit (86,469 registros, 21%) y Lobos (55,684 registros, 14%). Otros sitios con abundancias absolutas y relativas importantes fueron: Bahía San Jorge (34,768 registros, 9%), Santa Clara (18,769 registros, 5%) y el Delta del Río Colorado (20,184 registros, 5%). Por talla de los individuos, las abundancias de aves pequeñas (15-22 cm) y grandes (más de 36 cm) fueron similares (48% y 43%, respectivamente), las aves de talla media (24-30 cm) fueron menos comunes (8%). Los números encontrados permiten ubicar a Sonora entre los tres estados de la república con mayor abundancia de aves playeras invernantes (junto con Baja California Sur y Sinaloa).

Human exploitation has been a major driver of marine turtle population declines, particularly affecting naturally scarce species such as the pantropical hawksbill turtle. Although hawksbill sea turtles have been documented in the Gulf of California since the early 20th century, data on their historical demography during periods of high exploitation in this region are nonexistent. We investigated the size structure of hawksbill turtles from the Western Central Gulf of California by examining a unique sample of decorative taxidermies, corresponding to 31 specimens captured during fishing operations near Santa Rosalía, Baja California Sur, Mexico, between 1980 and 1990. An analysis of the curved carapace measures revealed a length range (nuchal notch to posterior of supracaudals) of 29.5–59.5 cm (mean = 38.75 ± 6.67 cm) and a width range of 25.0–51.5 cm (mean = 33.63 ± 5.66 cm), with 87% of specimens having lengths between 30 and 45 cm. Based on the carapace length measurements, we estimated the ages to be between 7 and 20 years, indicating that the population included juveniles. Our findings provide baseline data for an understudied period and region, suggesting that this area previously served as an important juvenile habitat. These results contribute essential historical demographic information for conservation planning.

Background: Population sex ratios and age structure are fundamental demographic parameters in shorebird studies, and their accurate estimation depends on unbiased capture methods. Methods: To identify potential capture biases, we evaluated the randomness of mist-net recaptures between sex and age classes of the Western Sandpiper (Calidris mauri) in La Paz Lagoon, Baja California Sur, Mexico. Results: A total of 856 individuals were captured and banded, of which 89 (10.4%) were recaptured. Observed and expected recapture frequencies did not differ significantly between sexes (67 observed vs. 62 expected males; 22 observed vs. 26 expected females), indicating no sex-related bias in recapture probability. In contrast, significant differences were detected between age classes (20 observed vs. 42 expected adults; 69 observed vs. 46 expected juveniles), demonstrating a clear age-related bias. The elapsed time between initial capture and recapture was similar for males and females but differed significantly between age classes: adults were most frequently recaptured after 51–75 days, whereas juveniles were recaptured predominantly after 1–25 days. Conclusions: Juveniles were more likely than adults to be captured and recaptured. The higher capture probability of juveniles may be associated with their greater mobility, resulting from their limited experience and lower social status.