Tricolored Blackbird (Agelaius tricolor)

Abstract

Breeding range of the Tricolored Blackbird in California. Overall outline of the range is stable, though numbers of breeders have declined dramatically. Colonies typically are largest in the Central Valley and are patchily distributed throughout, but particularly in the Coast Ranges and on the coastal slope.

Persistent panmixia despite extreme habitat loss and population decline in the threatened tricolored blackbird (Agelaius tricolor)

“…Our genome‐wide analyses also illustrate higher and more far‐reaching vagility by tricoloreds than previously known, though multiple studies employing bands on thousands of individuals have revealed large‐scale movements over major portions of the breeding range. These include, for instance, across the Central Valley (Beedy et al., 2018; DeHaven et al., 1975; Neff, 1942), along the coast (Wilson et al., 2016), and throughout southern California (Neff, 1942). However, because movements were not observed between the Central Valley and southern California, in particular by Neff (1942), the prevailing notion was that tricoloreds should be considered two separate demes split between these areas.…”

“…Finally, beyond the aforementioned biological causes, there is also an analytical component that should be considered. Our current N e calculation may be reduced by the presence of overlapping generations (Waples et al., 2014), which is likely in our dataset because adults are long‐lived (~12 years) and a lack of variation in molt and plumage beyond the second year limits age assessments (Beedy et al., 2018).…”

“…This L is based on sites that had at least 190X coverage (10X * the number of individuals used in the SFS projection) across a merged BAM file composed of the individuals that passed quality filters with and with no close relatives or PCA outliers (see results). Meanwhile, g is based upon a robust estimation from another Passerine (Brommer et al., 2004), and the known ages of first breeding of one year for female and two years for male tricoloreds (Beedy et al., 2018).…”

“…One such species experiencing severe impacts in the course of anthropogenic activities is the tricolored blackbird (tricoloreds; Agelaius tricolor ), a colonial songbird that is near endemic to California (Beedy et al., 2018). Tricoloreds are now listed as threatened at the state level after declining by an estimated 63% from 1935 to 1975 (Graves et al, 2013) and another 34% from 2007 to 2016 (Robinson et al., 2018).…”

“…Tricoloreds are now listed as threatened at the state level after declining by an estimated 63% from 1935 to 1975 (Graves et al, 2013) and another 34% from 2007 to 2016 (Robinson et al., 2018). These losses are primarily due to the destruction of the species’ historically preferred habitats for nesting, wetlands, and foraging, grasslands, by extensive agricultural and urban development (Beedy et al., 2018). As a consequence, whereas 93% of surveyed colonies nested in wetlands in the 1930s (Neff, 1937), tricolored colonies today use a broad range of nesting substrates, often including croplands and invasive species (Meese, 2017).…”