Zdravko Dolenec

First arrival dates of the Nightingale (Luscinia megarhynchos) to Central Croatia in the early 20th century and at the turn of the 21st century

Global climate change has important impacts on animal life-cycles. One of the responses to global warming is an earlier arrival time of many migratory bird species. The first arrival date of the Nightingale (Luscinia megarhynchos) in Central Croatia was studied for the periods of 1901–1917 and 1991–2005. Data were derived from the first spring observations and first capture data. A statistically significant advance of 11 ± 1.4 days was recorded. The difference in the mean April temperature between two study periods was significant, while changes in NAO winter index were not significant. Adequate data from the beginning of the 20th century exist; however, recent studies were done on a relatively short-term basis. Therefore, the analysis of two discrete datasets may help to fill the gaps in the knowledge about the climate change response.

Laying date of marsh tits Parus palustris in relation to climate change

Increasing evidence suggests that climate change affects bird breeding phenology and other life-history traits of wildlife. This study is based on the mean spring temperatures (February, March, April) and laying dates of first eggs of the marsh tit Parus palustris. We collected data from 1984 to 2004 for the Mokrice area in NW Croatia. Correlation between laying date and mean spring temperatures was significant. The relationship between mean laying date (y) and air temperature (x) can be expressed as y = 44.69 − 2.08x. Results indicate that spring temperatures are a good predictor of timing of laying eggs. Such long-term data could than be used in order to assess the effects on biological systems if human activities influence climate.

Spring migration characteristics of the House Martin, Delichon urbica (Aves: Hirundinidae) in Croatia: A response to climate change?

Many authors have discussed use of birds (and other organisms) as sensitive biomonitors for climate change. In this paper we investigate the long-term trends in first arrival dates of the long-distance migratory House Martin, Delichon urbica (Linneus, 1758), in north-western Croatia during the 28-year period. The aim of this paper is to identify possible relationship between arrival times and local spring air temperatures. Between 1981 and 2008 the House Martin arrived progressively earlier (5.9 days), probably in response to climate change. First arrival dates correlated significantly with increasing March-April mean temperatures. Correlation between mean spring air temperature and yearly temperatures were also statistically significant. Our results suggest that the arrival timing of the House Martin is influenced by spring air temperatures

Factors Affecting the Goldcrest/Firecrest Abundance Ratio in Their Area of Sympatry

The goldcrest (Regulus regulus) and the firecrest (Regulus ignicapilla) are sympatric over a large part of Europe, but with different abundance ratios. We studied the effects of geographical location, vicinity of the species range boundaries, habitat and climate factors on the goldcrest/firecrest abundance ratio. At the continental scale, a weighted multiple linear regression model resulted in four significant covariates: temperature, precipitation, forest type and occurrence rate (representing the vicinity of the species’ range boundaries). The firecrest dominates in warmer and more humid areas and its dominance is more pronounced in mixed forests. The projection of the model showed that in any combination of temperature, precipitation and occurrence rate, the probability to encounter the goldcrest is higher in coniferous forests. Studies in Croatia and the Czech Republic showed regional differences in habitat preferences related to forest type. A significant effect of the seasonal dynamics of precipitation was confirmed in Croatia. Climate change and changes in forestry may influence the distribution and abundance of these two Regulus species in Europe.

Detecting habitat changes using MODIS EVI images: a case study of Spoonbill Platalea leucorodia in Croatia Ugotavljanje sprememb v habitatih z uporabo posnetkov MODIS EVI: vzorčna študija žličarke Platalea leucorodia na Hrvaškem

Abstract The breeding population of Spoonbill Platalea leucorodia in Croatia, estimated at 154-275 breeding pairs, is classified as Endangered. The main reason for the unfavourable status is loss of breeding/feeding habitats. The purpose of the study was to detect changes in the habitat types previously assessed as important for Spoonbill’s feeding. The study area was chosen for two reasons: (1) the alluvial wetlands of the central part of the Sava River hold the biggest colony of Spoonbills in Croatia, and (2) availability of data on feeding ecology of Spoonbills along alluvial wetlands of the Sava River. We used the MODIS (Moderate Resolution Imaging Spectroradiometer) Enhanced Vegetation Index (EVI) as the main indicator for the changes in habitat structure along critical habitats for Spoonbills. The analysis identified areas with significant changes in EVI for habitat types important for feeding of the Spoonbills during the 2000-2008 period. Pastures, especially those with high wetness potential, changed in significant percentage despite conservation efforts in this habitat type. Changes in EVI were detected on ca. 9% of the pastures. For that reason we urge for better monitoring of the Spoonbill’s feeding habitats “in situ” and more specified characterisation of the reasons for the detected changes.

Intra-seasonal changes in reproductive strategy of a multi-brooded passerine: the tree sparrow Passer montanus

In order to evaluate how a multi-brooded bird species adapts its breeding strategy during the breeding season, we investigated variations in clutch size, egg traits and sex of the final eggs in a population of the tree sparrow Passer montanus in northwestern Croatia. Of the three clutches of the season, the second was the largest and it contained the largest eggs. Furthermore, the females followed the brood survivor strategy for the second clutch, while they chose the brood reduction strategy for the first and the third clutches. These results indicate that female tree sparrows adjusted their reproductive strategy over the course of the breeding season and invested the most resources in the second clutch. We hypothesise that their decisions may serve to maximise the number of offspring that they can successfully rear in a single breeding season.