Abstract
Cities are potentially stressful environments for birds for numerous reasons, including their high volumes of pedestrian and vehicular traffic. Native birds inhabiting cities tolerate such human disturbance, but may still potentially incur some cost that is reflected in body condition and the level of chronic stress experienced, unless they are inherently relatively insensitive to urban stressors. We compared body mass and condition, three erythrocyte variables and heterophil: lymphocyte ratios (HL) of adult Noisy miners (Manorina melanocephala) in urban Melbourne, Australia and its rural hinterland. Urban individuals had a significantly higher HL (mean 0.995) than rural con-specifics (0.719), suggesting that they may have been experiencing higher chronic stress levels. Body condition (mass-size residuals) and haematocrit were similar in urban and rural individuals, but urban individuals were a little heavier (~ 1%) and rural individuals had a 0.6 g dl higher whole blood haemoglobin concentration. There were no significant relationships between body condition indices and blood variables of the kind demonstrated in some bird species; their absence in Noisy miners may either reflect a lack of winter fattening or confirm that the occurrence of these relationships is species-specific.
Highlights
Proximity to humans and their activities can negatively influence bird assemblages, populations and individuals [1]
There are too few intra-specific comparisons of heterophil: lymphocyte ratios (HL) in free-living birds inhabiting contrasting environments to satisfactorily evaluate the biological significance of the observed modest difference in Noisy miners
The higher HL of urban Noisy miners was not associated with poorer body condition (MSR); urban individuals were slightly
Summary
Proximity to humans and their activities can negatively influence bird assemblages, populations and individuals [1]. Proximity to human disturbance disrupts vital behaviour [5], stimulates intraspecific aggression [6], reduces fecundity [7] and causes chronic stress and even mortality [8, 9] These effects apparently occur because birds often respond to humans as potential predators, even when they are harmless, and avoid close proximity to people or become ‘distressed’ when avoidance is impossible or uneconomical [10]. Cities have high densities of pedestrian and vehicular traffic, and physical and biotic features that can be problematic for some colonizing birds [11, 12] They are potentially quite stressful environments for members of many bird species. Perhaps the only birds that thrive in cities are
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