The Influence of Biological Factors on Haematological Values in Wild Marsh Harrier (Circus aeruginosus) Nestlings

Abstract

Marsh harrier (Circus aeruginosus) is a species with obligatory cainism, in which hatching asynchrony creates a pronounced size hierarchy in nestlings. The size-related competitive advantage of older nestlings means that they tend to dominate the younger ones, and brood reduction occurs in most nests. The aim of the study was to reference values and carry out a haematological examination in order to evaluate the physiological status and health of nestlings with respect to hatching order, brood size, and nest initiation date. To do so, we examined 19 nests with a total of 58 nestlings from a free-living population of this species located in fishpond complexes in the agricultural landscape of eastern Poland. Repeated blood samples (118 in all) were collected from nestlings. The following parameters were measured using fresh full blood: red blood cell count (RBC), haemoglobin level (Hb), white blood cell count (WBC), and plasma glucose level (Glu). The data were analysed using generalized linear mixed models and linear mixed models ((G)LMM). The study revealed that hatching order, but not brood size or nest initiation date, affected the physical condition of marsh harrier nestlings. Hb levels and RBC counts gradually decreased, whereas Glu levels and WBC counts increased from the first- to the last-hatched nestlings. This result points to the generally poorer condition of the youngest nestlings compared with their older siblings. The poor physiological condition of the youngest nestlings may consequently increase the likelihood of their perishing, and hence, of brood reduction.

Effect of Management of Grassland on Prey Availability and Physiological Condition of Nestling of Red-Backed Shrike Lanius collurio

“…Many authors have indicated that a reduction in the average haemoglobin level in chicks is associated with limited access to food (e.g., [65,98,193,194]) or poor food quality (e.g., [64,119]). Also, high haematocrit values are correlated with environmental food abundance and the absence of infections and parasites [195,196].…”

Storing prey in larders affects nestling haematological condition in the Red‐backed Shrike (Lanius collurio)

“…2020, Zaremba et al . 2021). Higher haemoglobin concentrations are a predictor of nestling survival from hatching to fledging (Kaliński et al .…”

“…2015), whereas higher WBC counts suggest higher stress levels in nestlings, a situation unfavourable to the proper development of nestlings (Zaremba et al . 2021). It has been documented in a few species of birds that the conditions experienced during early development can significantly affect physiology, behaviour and reproductive performance in later life (Hochachka & Smith 1991, Naguib et al .…”

“…The prey items are subsequently consumed mainly in the evening or the next morning, when temperatures are lower and insects are no longer or not yet very active (Hernandez 1995, Golawski et al 2020. The fact that limited access to food leads to a decrease in mean blood haemoglobin concentrations has been described in nestlings of many bird species (Minias 2015, Kali nski et al 2019, Lidman et al 2020, Zaremba et al 2021. Higher haemoglobin concentrations are a predictor of nestling survival from hatching to fledging (Kali nski et al 2015), whereas higher WBC counts suggest higher stress levels in nestlings, a situation unfavourable to the proper development of nestlings (Zaremba et al 2021).…”

“…The fact that limited access to food leads to a decrease in mean blood haemoglobin concentrations has been described in nestlings of many bird species (Minias 2015, Kali nski et al 2019, Lidman et al 2020, Zaremba et al 2021. Higher haemoglobin concentrations are a predictor of nestling survival from hatching to fledging (Kali nski et al 2015), whereas higher WBC counts suggest higher stress levels in nestlings, a situation unfavourable to the proper development of nestlings (Zaremba et al 2021). It has been documented in a few species of birds that the conditions experienced during early development can significantly affect physiology, behaviour and reproductive performance in later life (Hochachka & Smith 1991, Naguib et al 2006, so the better condition of shrike nestlings resulting from the availability of larders could lead to a greater survivorship of the birds, and possibly to higher future breeding performance.…”