Abstract
Data collected out of the breeding season suggest that House sparrows (Passer domesticus) from the urban populations are characterized by a smaller body size and poorer body condition compared to birds from rural populations. Considering an urbanized Eurasian Sparrowhawk (Accipiter nisus) and other potential predators, a new predator-prey dependency is developing that can also be a reason for the House sparrow’s poorer condition. This study was aimed at comparing the multivariate biometrical characteristics and few body condition indices of adult birds from urban and rural populations during the breeding season. It was hypothesized that a higher predation risk during the breeding season concerns mainly males, thus affecting their poorer condition. Most of the condition indices of males were significantly lower in the urban population. Males from the urban populations had lower body mass, shorter tarsus, longer alula, greater Kipp’s distance and higher wing pointedness index in comparison to the birds from rural populations, whereas these differences were not found between females. We suggest that the lower body condition and biometric differences in the analyzed birds are a means of adapting to the new predator-prey scheme in accordance to the tradeoff theory between starvation and predation risks. A lower condition of birds in poor foraging urban habitats and higher predation risk may be indicative of a declining population.
Highlights
The House Sparrow, known for its occurrence within human habitats, has become a widely distributed species, reaching vast numbers in urbanized areas
Multivariate comparisons of bird biometrics show a strong diversity of features among males and females (MANOVA: Wilks test: λ = 0.570; F8,124 = 11.687; P < 0.001) and among the urban and rural populations (Wilks test: λ = 0.679; F8,124 = 7.321; P < 0.0001), with a significant difference in the direction of feature variation between males and females of both populations
Considering the alula and tarsus length, as well as the Kipp’s distance, wing shape and body mass, females of the rural population showed no difference (Tables 1 and 2). Other features, such as the variability of wing, alula and tail length, the Kipp’s distance as well as the wing to tail length ratio, were lower in birds from the urban habitat compared to the rural population
Summary
The House Sparrow, known for its occurrence within human habitats, has become a widely distributed species, reaching vast numbers in urbanized areas. The previous comparative research on urban and rural populations of the House sparrow indicate that in urban areas the birds have a lower body mass, shorter tarsus and a weaker condition than in rural habitats (Liker et al 2008; Seress et al 2011) These differences by may explained by Shochat’s credit card (Shochat 2004) assumptions that the urban exploiter species reach high population numbers, which results in a significant increase in the number of individuals with a lower body condition compared to the populations in rural areas. Weaker or less competitive individuals will feed less and will never be able to reach their physical potential, but in accordance with the credit card hypothesis these smaller individuals will still have a high survivability rate and constitute a large part of the population, whereas only a small group of super competitors will manage to maintain a high body condition (Anderies et al 2007)
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