Diet
Dietary shifts throughout the annual cycle correspond to changes in gut
microbiota (Ren et al. 2017; Smits et al. 2017; Drovetskiet al. 2019). Kirtland’s Warblers shift from a fruit-rich diet in
The Bahamas to a diet composed primarily of insects in Michigan
(Deloria-Sheffield et al. 2001; Wunderle et al. 2010;
Wunderle et al. 2014). Firmicutes and Actinobacteria, which are
often associated with frugivorous diets and known to aid in digestion
through cellulose and carbohydrate degradation, were more abundant in
The Bahamas where the Kirtland’s diet is rich in fruit (Anand and
Kandula 2012; Segawa et al. 2019). The abundance of Cyanobacteria
throughout the sampling periods similarly shifts with decreased
frugivory exhibited by the Kirtland’s from The Bahamas to Michigan.
Cyanobacteria may be acquired as environmental byproduct; it may also be
represented by ingested chloroplasts (Brice et al. 2019). Though
Cyanobacteria is often removed from gut microbial studies (Knightet al. 2018), the proportional variation between sampling periods
further illustrates environmental and diet related differences
throughout the annual cycle.
Proteobacteria, often abundant in insectivorous species (Edenboroughet al. 2020) more than doubled in relative abundance from The
Bahamas to the second Michigan recapture period. This may be in response
to the shift in diet between locations. Additionally, specific lineages
of this phylum, such as genus Serratia , are known to produce
chitinase which facilitates the degradation of insects’ exoskeletons
(Rathore and Gupta 2015). We identified Serratia as significantly
abundant in the second Michigan sampling period, corresponding to the
insect-rich diet of that time.