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1. Seasonal Patterns of Fat Deposits in Relation to Migratory Strategy in Facultative Migrants

   https://doi.org/10.3389/fevo.2021.691808  

   Cornelius, Jamie M.; Hahn, Thomas P.; Robart, Ashley R.; Vernasco, Ben J.; Zahor, Dorothy L.; Glynn, Kenneth J.; Navis, Corrie J.; Watts, Heather E. (June 2021, Frontiers in Ecology and Evolution)

   null (Ed.)

   Physiological preparations for migration generally reflect migratory strategy. Migrant birds fuel long-distance flight primarily with lipids, but carrying excess fuel is costly; thus, the amount of fat deposited prior to departure often reflects the anticipated flight duration or distance between refueling bouts. Seasonal pre-migratory deposition of fat is well documented in regular seasonal migrants, but is less described for more facultative species. We analyze fat deposits of free-living birds across several taxa of facultative migrants in the songbird subfamily Carduelinae, including house finches ( Haemorhous mexicanus ), American goldfinches ( Spinus tristis ), pine siskins ( Spinus pinus ) and four different North American ecotypes of red crossbills ( Loxia curvirostra ), to evaluate seasonal fat deposition during facultative migratory periods. Our data suggest that the extent of seasonal fat deposits corresponds with migratory tendency in these facultative taxa. Specifically, nomadic red crossbills with a seasonally predictable annual movement demonstrated relatively large seasonal fat deposits coincident with the migratory periods. In contrast, pine siskins, thought to be more variable in timing and initiation of nomadic movements, had smaller peaks in fat deposits during the migratory season, and the partial migrant American goldfinch and the resident house finch showed no peaks coincident with migratory periods. Within the red crossbills, those ecotypes that are closely associated with pine habitats showed larger peaks in fat deposits coincident with autumn migratory periods and had higher wing loading, whereas those ecotypes associated with spruces, Douglas-fir and hemlocks showed larger peaks coincident with spring migratory periods and lower wing loading. We conclude that population averages of fat deposits do reflect facultative migration strategies in these species, as well as the winter thermogenic challenges at the study locations. A difference in seasonal fattening and wing loading among red crossbill ecotypes is consistent with the possibility that they differ in their migratory biology, and we discuss these differences in light of crossbill reproductive schedules and phenologies of different conifer species. 

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2. Habitat Urbanization, Circulating Glucose and Carotenoid Levels, and Body Condition Predict Variation in Blood Ketone Levels in House Finches (Haemorhous mexicanus) from the American Southwest

   https://doi.org/10.3390/birds6030034  

   McGraw, Kevin J; de_Souza_Penha, Victor Aguiar; DePinto, Kathryn N; Drake, Dean J; Crawford-Paz_Soldán, Elise; Pais, Danielle (September 2025, Birds)

   Real-time health assessment is crucial for diagnosing emerging threats to wildlife. Point-of-care instruments now allow detailed, affordable measurements of blood metabolites (e.g., glucose, triglycerides, ketones) in free-ranging animals. Ketones, however, remain understudied, especially in relation to environmental and life-history traits. Here, we assessed blood ketone variation in male House Finches (Haemorhous mexicanus) across two seasons (summer and winter) as a function of body condition, circulating glucose, carotenoids, lipid-soluble vitamins, and habitat urbanization (urban/suburban/rural). In both seasons, the interaction between capture site and glucose concentration predicted ketone levels: urban and suburban birds showed a negative relationship, while in summer, rural birds showed a positive one. Additionally, in winter, ketone levels were negatively associated with plasma carotenoids, indicating birds with higher carotenoid levels had lower ketone concentrations. These findings suggest that similar to patterns seen in biomedical research and our previous work on carotenoids and health, ketone status can serve as a valuable indicator of nutritional condition and fat metabolism in wild birds, particularly in the context of urbanization. 

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3. Using point‐of‐care devices to examine covariation among blood nutritional‐physiological parameters and their relationships with poxvirus infection, habitat urbanization, and male plumage coloration in house finches ( Haemorhous mexicanus )

   https://doi.org/10.1002/jez.2796  

   McGraw, Kevin J; de_Souza_Penha, Victor Aguiar (May 2024, Journal of Experimental Zoology Part A: Ecological and Integrative Physiology)

   Abstract The development of inexpensive and portable point‐of‐care devices for measuring nutritional physiological parameters from blood (e.g., glucose, ketones) has accelerated our understanding and assessment of real‐time variation in human health, but these have infrequently been tested or implemented in wild animals, especially in relation to other key biological or fitness‐related traits. Here we used point‐of‐care devices to measure blood levels of glucose, ketones, uric acid, and triglycerides in free‐ranging house finches (Haemorhous mexicanus)—a common songbird in North America that has been well‐studied in the context of urbanization, nutrition, health, and sexual selection—during winter and examined (1) repeatability of these methods for evaluating blood levels in these wild passerines, (2) intercorrelations among these measurements within individuals, (3) how blood nutritional‐physiology metrics related to a bird's body condition, habitat of origin (urban vs. suburban), poxvirus infection, and sex; and (4) if the expression of male sexually selected plumage coloration was linked to any of the nutritional‐physiological metrics. All blood‐nutritional parameters were repeatable. Also, there was significant positive covariation between concentrations of circulating triglycerides and glucose and triglycerides and uric acid. Urban finches had higher blood glucose concentrations than suburban finches, and pox‐infected individuals had lower blood triglyceride concentrations than uninfected ones. Last, redder males had higher blood glucose, but lower uric acid levels. These results demonstrate that point‐of‐care devices can be useful, inexpensive ways of measuring real‐time variation in the nutritional physiology of wild birds. 

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

   https://doi.org/10.3389/fevo.2022.817864  

   Goodchild, Christopher G.; VanDiest, Isaac; Lane, Samuel J.; Beck, Michelle; Ewbank, Hallum; Sewall, Kendra B. (February 2022, Frontiers in Ecology and Evolution)

   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. 

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5. Urban living can rescue Darwin's finches from the lethal effects of invasive vampire flies

   https://doi.org/10.1111/gcb.17145  

   Knutie, Sarah A.; Webster, Cynthia N.; Vaziri, Grace J.; Albert, Lauren; Harvey, Johanna A.; LaRue, Michelle; Verrett, Taylor B.; Soldo, Alexandria; Koop, Jennifer A.; Chaves, Jaime A.; et al (January 2024, Global Change Biology)

   Abstract Human activity changes multiple factors in the environment, which can have positive or negative synergistic effects on organisms. However, few studies have explored the causal effects of multiple anthropogenic factors, such as urbanization and invasive species, on animals and the mechanisms that mediate these interactions. This study examines the influence of urbanization on the detrimental effect of invasive avian vampire flies (Philornis downsi) on endemic Darwin's finches in the Galápagos Islands. We experimentally manipulated nest fly abundance in urban and non‐urban locations and then characterized nestling health, fledging success, diet, and gene expression patterns related to host defense. Fledging success of non‐parasitized nestlings from urban (79%) and non‐urban (75%) nests did not differ significantly. However, parasitized, non‐urban nestlings lost more blood, and fewer nestlings survived (8%) compared to urban nestlings (50%). Stable isotopic values (δ¹⁵N) from urban nestling feces were higher than those from non‐urban nestlings, suggesting that urban nestlings are consuming more protein. δ¹⁵N values correlated negatively with parasite abundance, which suggests that diet might influence host defenses (e.g., tolerance and resistance). Parasitized, urban nestlings differentially expressed genes within pathways associated with red blood cell production (tolerance) and pro‐inflammatory response (innate immunological resistance), compared to parasitized, non‐urban nestlings. In contrast, parasitized non‐urban nestlings differentially expressed genes within pathways associated with immunoglobulin production (adaptive immunological resistance). Our results suggest that urban nestlings are investing more in pro‐inflammatory responses to resist parasites but also recovering more blood cells to tolerate blood loss. Although non‐urban nestlings are mounting an adaptive immune response, it is likely a last effort by the immune system rather than an effective defense against avian vampire flies since few nestlings survived. 

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