American Robin (Turdus Migratorius) Blood Lead Levels May Reflect Elevated Soil Lead Levels: Further Consequences of the Flint Water Crisis

High levels of pollutants often occur in urban environments and can pose a threat to human residents as well as local wildlife. The Flint, Michigan water crisis was caused by the corrosion of pipe infrastructure, resulting in high levels of lead (Pb) leaching into the drinking water. Irrigation with contaminated water may have introduced lead into the soil causing another source of exposure to humans as well as wildlife. A widespread songbird species, the American robin (Turdus migratorius), feeds heavily on earthworms and ingests large amounts of soil during foraging. This study investigated the impact of the Flint water crisis on American robin blood lead levels (BLL) during the breeding season in southeast MI by comparing BLL of birds captured at irrigated sites of Flint to those captured at unirrigated sites in Flint, irrigated sites in a nearby city (Ypsilanti) and rural sites. Robins captured at irrigated Flint sites had nearly double BLL compared to unirrigated Flint sites and all other control sites. Body condition declined with increasing BLL at these irrigated sites of Flint, suggesting a measurable fitness impact of lead at these levels. Because BLL in American robins is known to reflect soil lead levels and soil lead is a known driver of BLL in children, robins may act as a bioindicator for urban communities. Further research should determine the efficacy of using robin BLL as a bioindicator of soil lead and how lead might be impacting body condition and other long-term fitness metrics in urban wildlife.

Natural and artificial scents do not increase egg rejection rates of model brood parasitic eggs by American robins (Turdus migratorius)

Hosts of obligate avian brood parasites can diminish or eliminate the costs of parasitism by rejecting foreign eggs from the nests. A vast literature demonstrates that visual and/or tactile cues can be used to recognize and reject natural or model eggs from the nests of diverse host species. However, data on olfaction-based potential egg recognition cues are both sparse and equivocal: experimentally-applied, naturally-relevant (heterospecific, including parasitic) scents do not appear to increase egg rejection rates in two host species, whereas unnatural scents (human and tobacco scents) do so in one host species. Here I assessed the predictions that (i) human handling of mimetically-painted model eggs would increase rejection rates, and (ii) applying unnatural or natural scents to mimetically or non-mimetically painted model eggs alters these eggs’ respective rejection rates relative to controls. I studied wild American Robins (Turdus migratorius), a robust rejecter species of the eggs of obligate brood parasitic Brown-headed Cowbirds (Molothrus ater). There was no statistical evidence to support either prediction, whereas poorer color-mimicry was still a predicted cause of greater egg rejection in this data set. Nonetheless, future studies could focus on this and other host species and using these and different methods to apply and maintain the scenting of model eggs to more directly test hosts’ use of potential olfactory cues in the foreign-egg rejection process.

Endocrine regulation of egg rejection in an avian brood parasite host

Parasite–host coevolution can lead to novel behavioural adaptations in hosts to resist parasitism. In avian obligate brood parasite and host systems, many host species have evolved diverse cognitive and behavioural traits to recognize and reject parasitic eggs. Our understanding of the evolution and ecology of these defences hinges on identifying the mechanisms that regulate them. We hypothesized that corticosterone, a hormone linked to stress response, vigilance and the suppression of parental behaviour, stimulates the rejection of foreign eggs by brood parasite hosts. We experimentally reduced circulating glucocorticoid levels with mitotane injections in American robins Turdus migratorius and found that the mitotane-treated birds rejected foreign eggs at a lower frequency compared to the sham-treated subjects. This is the first study to causally identify a potential mechanism of a widespread defence behaviour, and it is consistent with egg rejection being mediated by stress physiology.

The ecological context and fitness impact of categorical perception: a comment on Green et al.

Animals, including humans, must make sense of information, bombarding them from the enviroment, quickly and effectively. Categorical perception is one such process, and the evidence for it is increasing. We argue that the next step in the research of category-based decision making should be to study wild animals in the field and in behavioral contexts that have strong fitness-relevant impacts. We illustrate this point by the promise of categorical perception in the rejection of foreign egg colors by American robins (Turdus migratorius).