Abstract
This paper explores the ratio of the mass in the inflection point over asymptotic mass for 81 nestlings of blue tits and great tits from an urban parkland in Warsaw, Poland (growth data from literature). We computed the ratios using the Bertalanffy-Pütter model, because this model was more flexible with respect to the ratios than the traditional models. For them, there were a-priori restrictions on the possible range of the ratios. (Further, as the Bertalanffy-Pütter model generalizes the traditional models, its fit to the data was necessarily better.) For six birds there was no inflection point (we set the ratio to 0), for 19 birds the ratio was between 0 and 0.368 (lowest ratio attainable for the Richards model), for 48 birds it was above 0.5 (fixed ratio of logistic growth), and for the remaining eight birds it was in between; the maximal observed ratio was 0.835. With these ratios we were able to detect small variations in avian growth due to slight differences in the environment: Our results indicate that blue tits grew more slowly (had a lower ratio) in the presence of light pollution and modified impervious substrate, a finding that would not have been possible had we used traditional growth curve analysis.
Highlights
This paper uses nonlinear regression models to study the growth of passerine birds, blue tits (Cyanistes caeruleus) and great tits (Parus major)
We studied a shape parameter for bounded sigmoidal growth curves, the ratio of inflection point mass over asymptotic mass, whereby we used the five-parameter BP-model to estimate the ratio
Using data from literature, we illustrated the utility of this model by demonstrating that a higher level of urbanization was associated to a lower ratio, which in turn indicated a () slower growth towards the adult mass
Summary
This paper uses nonlinear regression models to study the growth of passerine birds, blue tits (Cyanistes caeruleus) and great tits (Parus major). Literature has considered various environmental factors that may affect growth, such as: tree cover [12], impervious surface [4, 13], pollution by light [14, 15] and sound [16,17,18], or nest interference by humans and pets [1, 2, 19]. All these factors are known to affect the breeding success. When clearly distinct environments were compared (forests and urban parklands), significant differences in the breeding success of blue tits [19] and in the growth of nestlings [10] could be established by the logistic and other simple models
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