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Himalayan weather has long been a mystery. The extreme logistical challenges that come with just trying to access the loftiest mountains have precluded all but a handful of weather stations [...]

Egg hatchability in birds is a critical component of individual reproductive success and is associated with eggshell integrity. Contaminants, such as DDT, can influence eggshell thickness and are known to cause population declines. Moisture content and temperature can also impact eggshell thickness, but the influence of environmental conditions on the natural variation in eggshell thickness in wild populations is not well understood. Our goal was to investigate the relationship between environmental conditions and eggshell thickness of Western Bluebird (Sialia mexicana) and Ash-throated Flycatcher (Myiarchus cinerascens) eggs from 1997 to 2013 on the Pajarito Plateau in northern New Mexico. We tested whether nesting elevation, temperature, precipitation, and drought conditions influenced eggshell thickness in these two secondary cavity-nesting species, while also looking at eggshell thickness over time. Over the 16 years, nonviable or abandoned eggs were collected, and the analyzed datasct included 330 bluebird eggs and 113 flycatcher eggs. There was a significant increase in eggshell thickness over time for both species. Flycatcher eggshells were correlated with higher temperatures, whereas bluebird eggshells were influenced by an interaction between temperature and drought severity. In drought conditions, bluebird eggshell thickness was positively correlated with temperature, whereas in wet conditions, eggshell thickness was negatively correlated with temperature. Thicker eggshells in drought conditions may be a way of reducing water loss from eggs, which occurs faster at higher temperatures. In the southwestern United States, frequent and severe drought, higher temperatures, and decreases in precipitation are all expected to continue. The structure of eggs will be important to consider regarding how species may or may not adapt to novel conditions or persist in new environments. Received 14 November 2022. Accepted 9 September 2023. Key words: Ash-throated Flycatcher, climate change, drought, nesting elevation, precipitation, temperature, Western Bluebird. La posibilidad de eclosion del huevo es un componente critico del exito reproductivo individual y esta asociada a la integridad de la cascara del huevo. Contaminantes como el DDT pueden influir en el grosor de la cascara de huevo y son conocidos como causa de declives poblacionales. El contenido de humedad y la temperatura pueden impactar el grosor de la cascara del huevo, pero la influencia de las condiciones ambientales en la variacion natural del grosor de la cascara de huevo en poblaciones silvestres no se entiende bien. Nuestro objetivo era investigar la relacion entre condiciones ambientales y el grosor de la cascara en huevos de azulejo Sialia mexicana y del copeton Myiarchus cinerascens de 1997 a 2013 en Pajarito Plateau en el norte de New Mexico. Probamos si las condiciones de elevacion de anidamiento, la temperatura, la precipitacion y la sequia influian en el grosor de la cascara de dos especies de aves anidantes secundarias en cavidades, midiendo tambien el grosor de cascara de huevo en el tiempo. En 16 anos, se colectaron huevos no viables o abandonados y la base de datos analizada incluyo 330 huevos de azulejo y 113 huevos de copeton. El grosor de las cascaras de huevo aumento considerablemente en el tiempo para ambas especies. Las cascaras de huevos de copeton se relacionaban mas con altas temperaturas, mientras que las de azulejo se relacionaban con la interaccion entre temperatura e intensidad de la sequia. En condiciones de sequia, el grosor de la cascara de huevo de azulejo se correlacionaba positivamente con la temperatura, mientras en condiciones humedas, el grosor de la cascara de huevo se correlacionaba negativamente con la temperatura. Las cascaras gruesas en condiciones secas pueden ser una manera de reducir la perdida de agua de los huevos, que ocurre mas rapido en altas temperaturas. En el sudoeste de los Estados Unidos, se espera que continuen las sequias frecuentes y severas, altas temperaturas y un decrecimiento en precipitacion. Sera importante considerar la estructura de los huevos para entender como las especies se adaptaran o no a nuevas condiciones o persistiran en los nuevos ambientes. Palabras clave: azulejo Sialia mexicana, cambio climatico, copeton Myiarchus cinerascens, elevacion del nido, sequia, precipitacion, temperatura., Climate change is a threat to biodiversity and directly impacts ecosystems and populations. Examples of these impacts are found across taxa and have become more severe in recent decades. Many [...]