Quantifying phenology and migratory behaviours of hummingbirds using single-site dynamics and mark-detection analyses

Nuanced understanding of seasonal movements of partially migratory birds
is paramount to species and habitat conservation. Using nascent
statistical methods, we identified migratory strategies of birds outfitted
with radio-frequency identification (RFID) tags detected at RFID feeders
in two sites in California, USA. We quantified proportions of migrants and
residents and the seasonal phenology for each movement strategy in Allen’s
and Anna’s hummingbirds; we also validated our methodology by fitting our
model to obligate migratory black-chinned hummingbirds. Allen’s and Anna’s
hummingbirds exhibited characteristics of facultative migratory behaviour.
We also quantified apparent annual survival for each migratory strategy
and found that residents had significantly higher probabilities of
apparent survival. Low survival estimates for migrants suggest that a high
proportion of birds in the migrant group permanently emigrated from our
study sites. Considered together, our analyses suggest that hummingbirds
in both northern and southern California sites partake in diverse and
highly plastic migratory behaviours. Our assessment elucidates the
dynamics underlying idiosyncratic migratory behaviours of two species of
hummingbirds, in addition to describing a framework for similar
assessments of migratory behaviours using the multi-state open robust
design with state uncertainty (MSORD-SU) model and single-site dynamics.