Data and code from: Cost of migration increased during an outbreak of highly pathogenic avian influenza virus

Migration is thought to be costly, such that challenges faced during
migration likely affect how birds migrate through direct selection on
migratory behavior. Survival throughout the annual cycle and conditions
that affect the survival costs of migration are therefore critical to our
understanding of the causes and consequences of migration. Estimating
daily survival throughout the annual cycle of migratory birds has only
recently become possible. We used over a decade of GPS tracking data from
186 migratory Buteo lagopus to quantify causes of mortality as
well as demographic, seasonal, and spatial variation in daily survival and
how survival consequences of migration changed during an outbreak of
highly pathogenic avian influenza virus. The cost of migration via direct
mortality varied between avian influenza and baseline study periods.
Surprisingly, mortality risk during typical spring migrations was lower
than in all other seasons, but mortality risk during the avian influenza
outbreak was higher during both spring and fall migrations. Additionally,
we found increased mortality risk in females during the avian influenza
outbreak but no sex differences during baseline periods. Hence, the
relative cost of migration was altered by the virus. During baseline
periods, mortality risk was highest during late fall migration and winter,
coinciding with increased anthropogenic-related mortalities at lower
latitudes. However, the number of deaths caused by avian influenza (n =
11) in a single year equaled the total number of deaths caused by
anthropogenic-related factors (n = 11; primarily collision trauma and
persecution) across all 12 study years. Overall, our study highlights how
added stressors such as disease outbreaks and anthropogenic factors may
exacerbate existing seasonal constraints by directly increasing mortality
risk.