INTRODUCTION
Omnivory implies nutrient acquisition from plant and animal sources
(Agrawal & Klein, 2000; Coll & Guershon, 2002; Singer & Bernays,
2003). Dietary sources utilized by omnivores may differ widely in
nutrient content and despite foraging different food types, many
omnivores have a primary or preferred diet. For example, most avian
omnivores are granivorous, frugivorous or herbivorous species that
incorporate protein-rich insects into their diets to complement their
protein-deprived primary plant diets (Coll & Guershon, 2002; Burinet al., 2016). Others are diet specialists or facultative
omnivores which do not necessarily require supplementation (Griffithet al., 2021). Where omnivory is obligate, deprivation of
supplementary diets will lead to nutrient limitation (Gillespie &
McGregor, 2000; Gillespie et al., 2012), whereas facultative
omnivores may be unaffected by such deprivation (Trichilo & Leigh,
1988; Milne et al., 1996; Milne & Walter, 1997).
Anthropogenic/natural environmental changes which may alter the
availability of specific food types can lead to nutrient limitation with
effects on body mass maintenance (Krieger et al., 2006; Papet al., 2008; Nwaogu et al., 2019; Filipiak & Filipiak,
2020), muscle and fat reserves (Pierce & McWilliams, 2004; Van den
Burg, 2009) and physiological parameters such as Packed Cell Volume
(PCV) and Haemoglobin Concentration (HBC) (Pyke et al., 2012).
For example, a protein-rich diet including insects supports the
maintenance of body form and function. Dietary protein deprivation may
thus lead to the breakdown of protein-rich tissues including muscles and
digestive organs (Piersma & Gill, 1998; Krieger et al., 2006).
The ability of animals to temporally adjust body reserves in response to
breeding and changes in environmental condition (Likness & Swason,
2011; Petit & Vezina, 2014; Nwaogu et al., 2017; Vezina et
al., 2020; Eikenaar et al., 2021) may also be impaired by diet
or nutrient limitation with effects on survival and fitness (Cooket al., 2004; see Harrison et al., 2011 for a review).
Also, the effects of nutrient limitation may be sex-specific because of
differences in breeding roles (e.g., Mallory et al., 2008),
physiology (e.g., Filipiak & Filipiak, 2020), and morphology (e.g.,
Fernández‐Montraveta & Moya‐Laraño, 2007).
In the absence of diet restriction, animals may face nutrient
limitations in nature due to changes in the quality of their preferred
diet (see Agrawal et al., 1999; Agrawal & Klein, 2000; Bravoet al., 2019), the energetic demand of cold condition (Swanson,
2010), and the occurrence of other energy/nutrient demanding periods of
the annual cycle such as breeding and moult (Murphy & Pearcy, 1993;
Cherel et al., 1994; Klaassen, 1995). This may lead to temporal
over-exploitation of body reserves (Milenkaya et al., 2013;
Ndlovu et al., 2017; Andersson et al., 2018; Awoyemi,
2020). To maximize nutrients intake during periods of limited nutrient
availability, animals may shift between diets or show preference for a
given food type (McWilliams et al., 2004; Lamperti et al.,2014; Kwiecinski et al., 2017) with sex-specific variation in
diet preference due to differences in morphology (Walker et al.,2014; Bravo et al., 2019), physiology, and breeding role
(Kwiecinski et al., 2017; Treidel et al., 2021).
In birds, body mass, pectoral muscle and fat scores indicate physical
condition in terms of energy and nutrient reserves (Milenkaya et
al., 2013). PCV and HBC on the other hand, are physiological indices
which may indicate overall health status (e.g., Garvin et al.,2007). Omnivorous birds in a changing Afrotropical environment are
useful surrogates for investigating how diet restriction and/or nutrient
limitation due to environmental changes and timing of annual cycle
events can influence body condition. The Village weaver Ploceus
cucullatus is an omnivorous tropical bird found throughout sub-Saharan
Africa (Craig, 2010). Its omnivorous foraging behaviour makes it
amenable to captive conditions and suitable for experimental diet
manipulation. This allowed the effects of nutrient deprivation on body
condition to be determined. In the wild, Village weavers exist in large
colonies often around water bodies or human settlements, but they thrive
well in captivity and are commonly kept as pets (Collias et al.,1986). Village weavers feed predominantly on grains (Collias and
Collias, 1970, Collias et al., 1986), but they also forage on
insects (Collias & Collias, 1970; Adegoke 1983), and fruits (Lahti,
2003; Yilangai et al., 2014). Males are polygynous. They build
nests but nestlings are predominantly fed by females (Collias &
Collias, 1970). Male weavers have brighter feathers compared to females
especially during the breeding period (Borrow & Demey, 2004).
In this study, we tested the effect of nutrient deprivation on the body
condition (body mass, pectoral muscle score, fat score, PCV and HBC) of
wild-caught captive Village weavers. First, we determined that grains
were the preferred diet of Village weavers, then we tested how
preference for grains, insects and fruits may vary over time and between
sexes. We expect weavers to show preference for grains compared to
fruits and insects during periods of higher energy demands such as under
colder environmental conditions. We also expected diet preference to
vary between sexes due to their differences in plumage colouration,
sex-roles and physiology. Secondly, we compared body condition indices
between male and female weavers fed on grains and fruits and those fed
on grains and insects over eight weeks. We expect; a deterioration of
body condition in weavers on both diet treatments if omnivory is
obligate, and a more pronounced deterioration in weavers deprived of the
more essential supplementary diet between insects and fruits. We
expected differences in how body condition varies over time and between
sexes if nutrient demands vary differently between sexes with changes in
environmental conditions over time.