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

Abstract

A central theme in the field of ecology is understanding how environmental variables influence a species’ distribution. In the last 20 years, there has been particular attention given to understanding adaptive physiological traits that allow some species to persist in urban environments. However, there is no clear consensus on how urbanization influences physiology, and it is unclear whether physiological differences in urban birds are directly linked to adverse outcomes or are representative of urban birds adaptively responding to novel environmental variables. Moreover, though low-density suburban development is the fastest advancing form of urbanization, most studies have focused on animals inhabiting high intensity urban habitats. In this study, we measured a suite of physiological variables that reflect condition and immune function in male song sparrows (Melospiza melodia) from rural and suburban habitats. Specifically, we measured hematological indices [packed cell volume (PCV), hemoglobin concentration, mean corpuscular hemoglobin concentration (MCHC)], circulating glutathione (total, reduced, and oxidized), oxidative damage (d-ROM concentration), antioxidant capacity, and components of the innate immune system [bacteria killing ability (BKA), white blood cell counts]. We also measured whole-animal indices of health, including body condition (scaled mass index length) and furcular fat. Song sparrows inhabiting suburban environments exhibited lower hemoglobin and MCHC, but higher body condition and furcular fat scores. Additionally, suburban birds had higher heterophil counts and lower lymphocyte counts, but there were no differences in heterophil:lymphocyte ratio or BKA between suburban and rural birds. PCV, glutathione concentrations, and oxidative damage did not differ between suburban and rural sparrows. Overall, suburban birds did not exhibit physiological responses suggestive of adverse outcomes. Rather, there is some evidence that sparrows from rural and suburban habitats exhibit phenotypic differences in energy storage and metabolic demand, which may be related to behavioral differences previously observed in sparrows from these populations. Furthermore, this study highlights the need for measuring multiple markers of physiology across different types of urban development to accurately assess the effects of urbanization on wildlife.

Individual variation within wild populations of an arid-zone lizard dictates oxidative stress levels despite exposure to sublethal pesticides

“…Bauerová et al ( 2017 ) and Herrera-Dueñas et al ( 2014 ) both found that oxidative stress was detected in RBCs, in conjunction with lower Hb and packed cell volume (PCV) concentrations in birds that inhabited urban areas opposed to rural areas. This is consistent with Goodchild et al ( 2022 ) where Song Sparrows ( Melospiza melodia ) inhabiting suburban areas displayed lower Hb concentrations compared to individuals inhabiting rural areas. However, the study did not find any significant differences in any of the oxidative stress markers tested (GSH, d-ROMs, HOCI neutralisation) between sites, which could suggest Hb concentrations are not dictated directly by urbanisation.…”

Are urbanization and brood parasitism associated with differences in telomere lengths in song sparrows?

“…Adult song sparrows in our urban and rural study sites show consistent behavioral differences (Hyman et al 2004, Evans et al 2010, Davies and Sewall 2016, Davies et al 2018, Fossett and Hyman 2021) and urban birds have higher reproductive success (Lane et al 2023). However, hormone concentrations, oxidative stress, and hematological measures do not reliably differ across habitats (Foltz et al 2015, Lane et al 2021, Goodchild et al 2022, nor is there detectable genetic differentiation between birds at our rural and urban sites (Brewer et al 2020). Song sparrows are a common host for brown-headed cowbirds (Hauber and Russo 2000), and at our study sites brood parasitism occurs at high rates in urban habitats but is very rare in rural habitats (Lane et al 2023).…”

“…These measures have the potential to reveal both pathological effects of living in urban habitats and provide insight into the adaptive mechanisms underpinning responses that facilitate urban living (Isaksson 2015). Previous work has shown associations between urbanization and altered levels of hormones, oxidative stress, hematological parameters, and immune function (Bonier 2012, Isaksson 2015, Isaksson 2018, Goodchild et al 2022, Bonier 2023. Additionally, there is increasing interest in the impacts of urbanization on telomeres -tandem repeats of DNA and a shelterin protein complex at the end of chromosomes (Shay andWright 2019, Salmón andBurraco 2022).…”

Indirect effects of urbanization: consequences of increased aggression in an urban male songbird for mates and offspring

“…This refutes both the idea that urban males are facing a trade-off between territorial defense and parental care, and that urban habitats compromise male parental care. Previously, researchers found that urban male songbirds in this population had better body condition and access to greater fat reserves compared to rural (Goodchild et al, 2022), suggesting that birds in urban habitats are of higher quality than their rural counterparts and are therefore released from constraints experienced by other birds (Reznick et al, 2000). Additionally, urban males likely have different time and energy budgets compared to rural.…”