Radio transmitters do not influence physiological traits of wintering Grasshopper Sparrows ( Ammodramus savannarum ) in the Chihuahuan Desert of Mexico

Abstract

Radio transmitters are a commonly used method that allows researchers to obtain valuable biological and ecological data from avian populations. However, transmitters might negatively affect survival due to the physiological cost of carrying a device. The negative fitness effects of transmitters are likely to vary interspecifically. Therefore, understanding responses to transmitters by birds can help minimize researcher impact and refine the vital rate estimates derived from these approaches. In this study, we investigated the potential negative impact of radio transmitters on two physiological parameters (heterophil-to-lymphocyte ratio and scaled mass index) on the Grasshopper Sparrow ( Ammodramus savannarum ) during the non-breeding season in northern Mexico. Specifically, we used two sampling approaches: repeated measures and independent samples. With repeated measures, most radio-tagged individuals maintained similar values in their scaled mass index across the winter, and showed a statically non-significant increase in this variable. In addition, at the population level (independent samples), we observed no significant difference in the use of transmitters, based on the two physiological parameters. Our results for the non-breeding season are consistent with previous studies where researchers have reported no effects of radio transmitters on physiological parameters. In summary, the study provides insights into the lack of a transmitter effect on chronic stress and body mass index in this species, conducted in a challenging environmental stage of the annual cycle and within a grassland priority conservation area.

Keywords

• chronic stress
• grasshopper sparrow
• grasslands
• heterophil-to-lymphocyte ratio
• radio-transmitter effect
• physiological traits
• scaled mass index
• wintering