Birds undergo many morphological and physiological changes in preparation for migration, such as zugunruhe, hyperphagia leading to pre-migratory fattening, and heightened immune system function. Birds in poor condition, without insufficient reserves, may not complete or even begin migration. Many aspects of the physiological changes occurring during migration are poorly understood, especially in raptors. I investigated the relationship between body condition and heterophil to lymphocyte (H:L) ratios in fall migrating northern saw-whet (Aegolius acadicus) and flammulated owls (Otus flammeolus). Blood smears were made and 200 white blood cells counted on each smear. There was a significant negative relationship between H:L ratios and body condition index in northern saw-whet owls: as body condition decreased, H:L ratios increased. An increased H:L ratio is indicative of increased stress on the immune system. There was no detectable relationship between H:L ratio and body condition index in flammulated owls; however, the sample size was low. While the H:L ratio may be a good index for chronic stress, this ratio may not be as useful during migration when most migrating birds are in good condition.
A relationship has been shown between hemoparasites and body condition during the breeding season. I investigated this relationship during the migration season in the same owl species as above. Blood smears were made and hemoparasites counted per 200 white blood cells. For northern saw-whet owls in 1999, prevalence was 53% (n = 30). In year 2000, northern saw-whet owls, prevalence was 47% (n = 70). In year 1999, flammulated owls had a prevalence of 44% (n = 16). In 2000 prevalence was 33% (n =6). Three genera of hemoparasites were found in both owl species: Haemoproteus spp., Leucocytozoon spp., and Trypanosoma spp. Northern saw-whet owls were primarily infected with L. ziemanni, while flammulated owls were primarily infected with H. noctuae and H. syrnii. There was no detectable correlation between presence/absence of parasites and body condition index in flammulated owls.
Traditionally, northern saw-whet owls are sexed in the field using a morphometric chart that was created from a discriminate function of mass and wing. However, this chart has an area of overlap between small females and large males requiring those birds to be classified in the field as unknown sex. Moreover, in flammulated owls, there is not enough dimorphism to allow them to be sexed by external measurements. I compared three methods of DNA sexing using two sets of primers: P2 and P8, and P2550 and P2718. All methods gave consistent and comparable results, and were used to successfully sex 44 flammulated owls and 210 northern saw-whet owls. DNA sexing allowed me to assign sex to 112 of 141 owls that would have been classified as unknown by the chart. When compared to DNA sexing results, morphometric methods had an accuracy rate of 97% on owls definitively sexed by the morphometric chart. DNA sexing is recommended for monomorphic species and any birds that cannot be sexed by morphometric means.