Effects of an anthropogenic diet on indicators of physiological challenge and immunity of white ibis nestlings raised in captivity

Abstract

When wildlife forage and/or live in urban habitats, they often experience a shift in resource availability and dietary quality. Some species even use human handouts, such as bread, as well as human refuse, as a large part of their new diets; yet the influences of this nutritional shift on health and survival remain unclear. American white ibises are increasingly being seen in urban areas in Florida; they collect handouts, such as bread and other food items, from humans in parks, and are also found foraging on anthropogenic sources in trash heaps. We hypothesized that the consumption of these new anthropogenic food sources may trigger increases in indicators of physiological challenge and dampen immune responses. We tested this experimentally by raising 20 white ibis nestlings in captivity, and exposing 10 to a simulated anthropogenic diet (including the addition of white bread and a reduction in seafood content) while maintaining 10 on a diet similar to what ibises consume in more natural environments. We then tested two indicators of physiological challenge (corticosterone and heat shock protein 70), assessed innate immunity in these birds via bactericidal assays and an in vitro carbon clearance assay, and adaptive immunity using a phytohemagglutinin skin test. The anthropogenic diet depressed the development of the ability to kill Salmonella paratyphi in culture. Our results suggest that consuming an anthropogenic diet may be detrimental in terms of the ability to battle a pathogenic bacterial species, but there was little effect on indicators of physiological challenge and other immunological measures.

Variation in Hematological Indices, Oxidative Stress, and Immune Function Among Male Song Sparrows From Rural and Low-Density Urban Habitats

“…For example, future work should examine whether variation in hemoglobin concentrations among rural and suburban sparrows is associated with resting and maximum metabolic rates. Additionally, hemoglobin synthesis can be suppressed by poor nutrition (Minias, 2015), so future studies should also examine whether availability of micronutrients on the landscape influences the metabolic phenotypes of rural and suburban song sparrows (Coogan et al, 2018;Cummings et al, 2020a). Finally, to better understand the ecological relevance of varying hemoglobin levels, it is critical to understand whether hemoglobin concentration is related to breeding ecology and fitness outcomes (e.g., survival and reproductive success).…”

Nature versus nurture: Structural equation modeling indicates that parental care does not mitigate consequences of poor environmental conditions in Eastern Bluebirds (Sialia sialis)

“…In addition, we did not estimate food quality, but food quality may have impacted condition in the birds we studied. Low‐quality food is associated with decreased measures of avian condition, such as immune function (Cummings et al, 2020) and body mass (Wright et al, 1998). Similarly, when European Starlings brought larger portions of low‐quality food, nestling growth rate was slower than when parents provided more digestible food (Wright et al, 1998).…”

Macronutrients, the microbiome, and illness-induced feeding behavior: Do macronutrients shape avian immune responses?

“…Diet can also directly affect immunity without the mediation of hormones. In captive white ibis, birds that were fed anthropogenic dietary items like white bread had reduced bacterial killing ability, but corticosterone levels and the other immune parameters investigated were unaffected by diet treatment (Cummings et al 2020). Other work has found that restriction of dietary protein can limit immune activity (Lee et al 2006, Povey et al 2009) and high lipid diets can increase mortality rates during infection (Adamo 2008, Adamo et al 2010.…”