Introduction
Niche partitioning has an important role in the coexistence of multiple
species with similar ecology (Levine and HilleRisLambers 2009). It is
rather natural that ecologically similar species use different resources
such as foods (Hasui et al. 2009) and nest sites (Kosinski and Winiecki
2004, Vierling et al. 2009) depending on the availability in the shared
habitat to avoid conflicts and competitions. Knowing strategies that
animals adopt to coexist with other species is essential not only for
understanding the biodiversity and ecosystems but also for elucidating
factors that shape their behavior and cognitive functions.
Estrildid finches are one of the most well-studied songbird families
regarding their behavior from its neural mechanisms to evolution (e.g.,
courtship song: Catchpole and Slater 2003, Soma and Garamszegi 2015;
nest-building: Bailey et al. 2014, Guillette and Healy 2015, Hall et al.
2015), while we have limited knowledge of their wild behavior and the
environmental conditions in many species. Blue-capped cordon-bleus
(Uraeginthus cyanocephalus ) and red-cheeked cordon-bleus
(Uraeginthus bengalus ) are socially monogamous, biparental
Estrildid finches from Africa. Male blue-capped and red-cheeked
cordon-bleus, as their names suggest, have blue caps and red cheeks,
respectively (Fig. 1). Female blue-capped cordon-bleus have brighter
blue plumage and pink beak than red-cheeked (Fig. 1). They are sister
species and have similar life history and breeding behavior, and their
habitat overlaps in East Africa (Goodwin 1982, Hockey et al. 2005,
Billerman et al. 2020). Past literature generally mentioned the
ecological and behavioral similarities between the two species and
usually neglected the possibility of adopting different behavioral
strategies to avoid conflicts in the shared habitat.
The nest building behavior of cordon-bleus is characteristic in several
ways. They build their nest in trees mainly using grasses, but sometimes
take over weaver (Ploceus spp. or Bubalornis spp.) old
nests (Fig. 2b, c). They often build a nest near wasp nests
(Hymenoptera: Vespidae) to reduce the predation risk (Fig. 2a, c, d;
Goodwin 1982, Hockey et al. 2005, Beier and Tungbani 2006, Billerman et
al. 2020). During my fieldwork in Tanzania, I observed that cordon-bleus
used the same nesting strategies as previously reported (Fig. 2). The
primary purpose of the expedition was to observe the multimodal
courtship display of wild cordon-bleus (Ota 2020), but I could also
observe nest-building behavior and the nests during the study (Fig. 2,
Movie S1). When attempting to observe the courtship behavior of
cordon-bleus, I usually focus on individuals holding a piece of nest
materials on their beak since cordon-bleus perform courtship displays
with holding them (Ota 2020). Cordon-bleus holding a piece of nest
materials often carried them to their nests (Movie S1) rather than using
them for courtship. In addition, I confirmed that two species of
cordon-bleus actually inhabited and breed sympatrically at my field site
(see results, Fig. 3), so I expected it would be an ideal opportunity to
examine their nesting strategies and the species differences.
I hypothesized that the adopting nesting strategies and their frequency
vary between two cordon-bleus, which can avoid resource competition. I
recorded the positions and surrounding conditions of the nests and
tested if there were species differences. I will also describe some
observational findings of nest characteristics in two cordon-bleus.