Meeting Abstract
Reproduction often requires large investments in time and resources and the body undergoes significant changes to meet these energy demands. Investments in survival can also be very energy costly and animals usually time reproduction to occur during the least challenging time of year (e.g., spring and summer). Blood physiology (e.g., hematocrit and red blood cells (RBC) size) may reflect such seasonal resource demands given that these factors probably affect oxygen delivery to working tissue; however, most organisms breed only when environmental parameters are comparatively benign. Some organisms, however, like the red crossbill, Loxia curvirostra breed in both summer and winter allowing the opportunity to compare differences between seasons and reproductive condition independently. We measured how blood physiology responds to environmental parameters and reproductive investment by looking at hematocrit and red blood cell size over seasons and various other physiological and environmental parameters. Our data suggest that crossbills have larger RBCs but lower hematocrit in spring compared with other seasons. There were fewer breeding birds in spring and the high levels of fat deposition coupled with known behavioral patterns suggest a migratory phase. Breeding was most prevalent in summer and winter when hematocrit was higher and cell size was lower – agreeing with the higher hematocrit and lower cell size in reproductively active birds independent of season. We discuss these results in light of behavioral ecology of crossbills, metabolic demand and oxygen delivery dynamics.
