Age-dependent changes in biometrics indicate senescence in the European Blackbird <i>Turdus merula</i>

<p><b>Capsule:</b> A 19-year study of European Blackbirds <i>Turdus merula</i> confirms that senescence is associated with a decrease in condition measured by wing length but bills become progressively longer with age.</p> <p><b>Aims:</b> To explore the correlations between biometrics of Blackbirds and age, to identify possible links with senescence.</p> <p><b>Methods:</b> During the 19 years of the study, 801 birds of known age were measured: 431 males and 370 females, aged from 2 to 10 years. Among these 91 males and 50 females were retrapped at least one moult later. For each bird, there were at least one set of measurements when fully grown.</p> <p><b>Results:</b> Wing length increased until the sixth year of life after which it started to decrease. An increase in bill length throughout the lifetime was found in both sexes.</p> <p><b>Conclusion:</b> Changes in wing length correspond with an earlier study of this population suggesting the onset of senescence after the fifth to sixth calendar year of life.</p

Estimated smoothing functions modeling Greater Scaup <i>Aythya marila</i> abundance in relation to the area of occurrence of Zebra Mussel <i>Dreissena polymorpha</i> (km², left-hand panel– 5A) and Zebra Mussel density (tons per 1 km², right-hand panel– 5B) from the best-supported model.

<p>Shaded areas denote 95% confidence intervals around the smoothing functions.</p

Correlation between Zebra Mussel <i>Dreissena polymorpha</i> biomass and biomass of all other food taxa in the digestive tracts of 32 Greater Scaup <i>Aythya marila</i> from the Odra River Estuary during the non-breeding seasons in the years 2008–2013.

<p>Each point represents a single bird.</p

The study area—the Odra River Estuary, NW Poland, bordered by a bold line.

<p>The study area—the Odra River Estuary, NW Poland, bordered by a bold line.</p

Greater Scaup <i>Aythya marila</i> and its flocks in the Odra River Estuary.

<p>A—Scaup flock in the Miroszewo (MI) subarea, 16.10.2013, photo by D. Marchowski. B and E—part of a line of Scaup directly above the Zebra Mussel aggregation in the Miroszewo (MI) subarea, B—16.10.2013, E—09.10.2013, photo by D. Marchowski. C—adult male of Scaup, Pomeranian Bay near Świnoujście, 16.02.2014, photo by D. Kilon. D—Scaup females in the Pomeranian Bay near Świnoujście, 16.02.2014, photo by D. Kilon. F—part of a 30 000-strong flock of Scaup directly above the Zebra Mussel aggregation in the Krzecki Wyskok (KW) subarea, 16.10.2013, photo by D. Marchowski.</p

Spatial distribution and abundance of Greater Scaup <i>Aythya marila</i>–mean number of individuals per 1 km² based on censuses in the non-breeding period (October to April, 2002–2014), see also Table 2.

<p>(A). Spatial distribution and biomass of Zebra Mussel <i>Dreissena polymorpha</i> on the 2x2 km modeling grid (B).</p

The percentage of the 156 square/month combinations for both rural (R) and urban (U) areas in which each species (at least one individual) was recorded, the total number of individuals (n) recorded, the mean number for rural and urban areas, the percentage of records recorded from urban areas (%U), whether the model was based on negative binomial (N) or Gaussian (G) distribution, and the significance level of rural/urban, month and interaction terms from GLMM (month means not shown to save space).

<p>Benjamini-Hochberg corrected significance level (BH) is given in brackets under a header of the columns for each hypothesis. Codes are used in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130299#pone.0130299.g002" target="_blank">Fig 2A</a>. Where rural/urban comparisons were significantly different the higher mean is in bold. Species in alphabetical order of Latin names.</p><p>The percentage of the 156 square/month combinations for both rural (R) and urban (U) areas in which each species (at least one individual) was recorded, the total number of individuals (n) recorded, the mean number for rural and urban areas, the percentage of records recorded from urban areas (%U), whether the model was based on negative binomial (N) or Gaussian (G) distribution, and the significance level of rural/urban, month and interaction terms from GLMM (month means not shown to save space).</p

Best generalized linear mixed models (GLMM) describing the abundance of the 10 most numerous bird species during the winter.

<p>The Akaike information criterion score (AICc), the -2log, difference between the given model and the most parsimonious model (Δ) and the Akaike weight (<i>w</i>) are listed. Explanation of variable codes: Feeders—number of bird feeders, CitySize—human population size in the city, Month—month of survey (December vs. January), Environment—type of the environment (urban vs. rural), Longitude—geographical longitude, PCA1—the first principal component of environmental variables describing the gradient of increasing proportion of open agricultural habitats, PCA2—the second principal component of environmental variables describing gradient from semi-natural grasslands to intensively managed amenity grasses.</p><p>Best generalized linear mixed models (GLMM) describing the abundance of the 10 most numerous bird species during the winter.</p

Location of the study areas.

<p>Location of the 26 paired areas used to study winter differences in birds between rural and urban environments in Poland.</p

Averaged estimates of the function slopes of variables present in the most parsimonious GLMMs describing the corrected abundance of the 10 most numerous recorded bird species.

<p>Standard errors (SE) and 95% confidence limits (CL) are also presented. Tests of significance of variables are given in the final two columns. Explanation of variable codes: <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0130299#pone.0130299.t005" target="_blank">Table 5</a>.</p><p>* A reference variable</p><p>Averaged estimates of the function slopes of variables present in the most parsimonious GLMMs describing the corrected abundance of the 10 most numerous recorded bird species.</p