Wild Bird Reproduction: Neuroendocrinology, Conservation Biology, and Environmental Threats.

Birds are among the most diverse and threatened vertebrates on the planet. Occupying a vast array of global ecosystems, avian species are adapted to a variety of climates and enduring a range of stressors including anthropogenic and climate-related challenges. However, despite their adaptations to varied ecosystems, avian populations are declining at an alarming rate as seen in data from various global regions. In addition, illegal trade and loss of habitat impose significant stress on birds. It is critical to understand the life history of short- and long-lived birds, unique characteristics of birds including migratory patterns, effects of environmental chemicals, and other stressors on vulnerable life stages. Moreover, the ability to monitor wild populations is critical, and field-friendly health metrics must be developed. Understanding avian biology across the diversity of species and their critical resource requirements is critical to conservation. Although the hypothalamic-pituitary-gonadal (HPG) axis and neuroendocrine regulation of reproduction have many conserved mechanisms, the unique characteristics of avian physiology must be understood for effective conservation. The deleterious effects of developmental exposures to environmental chemicals, especially endocrine-disrupting chemicals (EDCs), can alter lifetime reproduction, and the adverse effects are exerted differentially in songbirds (altricial) versus precocial species. Examples are provided for the involved physiological mechanisms, with consideration of neuroendocrine mechanisms that modulate responses to environmental stressors. In addition, the role of vultures as scavengers and the demise of Old World vultures are presented as a case study.