Spatial and Temporal Variation in Heterophil-to-Lymphocyte Ratios of Nestling Passerine Birds: Comparison of Blue Tits and Great Tits

Abstract

Environmental factors affecting trophic conditions act as stressors on nestling altricial birds. Access of parental birds to a sufficient supply of food in a limited period of the nestling stage differ in time and space, depending on nesting habitat, prey density and weather conditions. Heterophil-to-lymphocyte ratio (H/L) is considered as a reliable indicator of prolonged stress reaction in birds. In this study we examine if variation in H/L shows consistent spatio-temporal patterns in nestlings of two parids, blue tit Cyanistes caeruleus and great tit Parus major. We found that blue tit nestlings had on average higher H/L than great tit nestlings, which corresponds with the ecological sensitivity of these species. In both species H/L was higher in a poor parkland habitat than in a high quality forest habitat. In nestling blue tits, higher H/L values occurred in years characterized by more extreme weather conditions and worse caterpillar availability. Such consistent patterns of variation in the H/L ratio of nestling blue tits and great tits suggest that, when age-dependent effects are controlled, the ratio can be used as an indicator of physiological stress that is generated by food-related stressors differing in space and time. In particular, elevated H/L ratios are indicative of human-induced changes in the structure of breeding habitats.

Leukocyte profiles indicate nutritional, but not moulting stress in a migratory shorebird, the Common Snipe (Gallinago gallinago)

“…However, most research suggest that unfavourable feeding conditions can provoke changes in leukocyte profiles of wild birds. Elevated H/L ratios have been recorded in passerine nestlings raised in poor-quality territories with low availability of food resources (Soursa et al 2004;Bańbura et al 2013). A similar relationship was found in juvenile Common Kestrels (Falco tinnunculus) (Müller et al 2011).…”

Spatial variation in haemoglobin concentration of nestling Blue Tits (Cyanistes caeruleus): a long-term perspective

“…This difference in condition between both study areas reflects differences in trophic conditions, as described by Naef-Daenzer and Keller (1999). Our study areas considerably differ in caterpillar productivity, with the forest site being characterized by 2-5 times higher abundance of caterpillars than the parkland site (Marciniak et al 2007;Bańbura et al 2013). Additionally, long-term year-to-year changes in haemoglobin concentration were correlated with frassfall peaks in the forest site.…”

“…A parent emits alarm calls and hesitates to approach the nest (Müller et al 2006). Bańbura et al (2013) examined the heterophil-to-lymphocyte ratio (H/L) in Blue Tits at both our study areas and found that nestlings had on average higher level of the H/L in the urban parkland study area than in the forest study area. The H/L is considered as a reliable indicator of chronic stress reaction in birds (Gross and Siegel 1983;Ots et al 1998;Moreno et al 2002;Davis et al 2008).…”

“…The parkland site (51°45 0 N; 19°24 0 E), about 80 ha (including the zoological garden of 16 ha and the botanical garden of 64 ha), has a highly fragmented tree cover (formed artificially) and is one of the major recreation and entertainment areas in Łódź, which is associated with strong human disturbance over the entire breeding season (Bańbura et al 2013;Glądalski et al 2015b). We assess that in 2008-2013 the average number of visitors to our parkland study site in May, as the main period of the nestling stage of Blue Tits, is about 75,000.…”

“…Because the measuring of habitat quality in a direct way is often not feasible, the evaluation of individual condition offers an alternative method to assess habitat quality (Homyack 2010;Ellis et al 2012). Body condition indices have been used to evaluate impacts of stressors and disturbances, assessing habitat fragmentation or to provide insights into the nutritional status of animals in different habitat types Bańbura et al 2013;Milenkaya et al 2013;Kaliński et al 2014;Minias 2015). Currently, relatively few landscape ecologists employ physiological approaches to evaluate habitat quality.…”