Zapletal T.,Mendel University in Brno |
Mares J.,Mendel University in Brno |
Jurajda P.,Ustav Biologie Obratlovcu |
Vsetickova L.,Ustav Biologie Obratlovcu
Acta Universitatis Agriculturae et Silviculturae Mendelianae Brunensis | Year: 2012
Food composition of common bream (Abramis brama, L.) was studied in the shallow, meso-eutrophic, Hamry reservoir (Czech Republic). Fish were sampled during the daytime in the pre-spawning period (April), the post-spawning (June), summer (July) and autumn (October) in 2011. The bream sampled comprised two main size groups: small, 124-186 mm; and large, 210-315 mm standard length. Twenty specimens of each size group (except April - 40 large fish) were taken for analysis on each sampling occasion. Food composition was evaluated using gravimetric methods. Over the whole season, detritus and aquatic vegetation were the dominant dietary items taken. During summer, the diet of large bream comprised mainly aquatic vegetation. Benthic macroinvertebrates and zooplankton formed a minor part of bream diet over the whole season. Specific food habits of bream could be explained by specific conditions within the reservoir and available food resources.
Prochazka P.,Ustav Biologie Obratlovcu |
Jelinek V.,Ustav Biologie Obratlovcu |
Pozgayova M.,Ustav Biologie Obratlovcu |
Honza M.,Ustav Biologie Obratlovcu
Sylvia | Year: 2012
Age is an important indicator of a bird's experience affecting the timing of migration, mortality, social status and reproductive success. Researchers and ringers should be thus able to age the studied birds correctly. However, a common method of ageing based on the contrast between retained juvenile feathers and adult plumage cannot be applied in many species after complete moult. We tested a simple score combining the colouration of iris, tarsus and tongue spots in the Great Reed Warbler (Acrocephalus arundinaceus). This method was developed to discern young, second calendar-year birds (2K) from adult, after second calendar-year (+2K) individuals in spring. We used 272 score values of 164 retrapped birds with age known from ringing data. The two age categories differed significantly in score, the values of which decreased with age of the birds. Juvenile characters disappeared faster in males than in females. An analysis of reliability of the method showed that the border value originally suggested by Bensch et al. (1998) is the best for females. However, this criterion would misclassify a significant proportion of 2K males as +2K birds which would significantly decrease the sample size in 2K males. We propose a more reliable criterion allowing for sex differences and leaving a certain proportion of birds with intermediate score values as undetermined (+1K). Similar scores would be desirable for other species where the plumage after the first complete moult does not allow reliable age determination.