Population decline of the House Sparrow Passer domesticus in orange groves of eastern Spain

Full article

Published:

Volume 49(2), December 2002. Pages 195-209.

Language:

Spanish

Original title:

Tendencia decreciente de la población de Gorrión Común Passer domesticus en los naranjales del este de España

Keywords:

colonies, growth rate, House Sparrow, orange groves, Passer domesticus, population, rainfall, temperature, tree cover

Abstract:

This study presents the trend of a population of House Sparrows in a plot of 16.92 ha during 27 years (1975-2001) in eastern Spain. Each year we determined the number of breeding pairs in the plot by means of exhaustive nest searching. The results showed a dramatic decline of the breeding population from 114 pairs in 1977 to 6 in 2001 (No. breeding pairs = 5709.23 – 2.85(YEAR); R2 = 0.75, F1,25 = 76.59, P<<0.001). Meteorological variables did not explain the population decline. We analysed four meteorological variables: i) the sum of rainfall during July and August, the dry period; ii) the sum of rainfall from September to October, a period of high rainfall in eastern Spain that could produce floods; iii) the average maximum temperatures from July to August, the warmest period; and iv) the average minimum temperatures during December and January, the coldest period. The population growth rate (r) rwas inversely related to the sum of rainfall during September and October (r = 0.159 – 0.0019(MAXIMUM RAINFALL), R2 = 0.24, F1, 24 = 7.22, P = 0.013; Fig. 3). Changes in the location of House Sparrow colonies did not explain the decline since colonies located in groves around the study area also disappeared (Fig. 4). From 1975 to 1988 the number of trees declined and then increased until 2000 (Fig. 5). However, the breeding population of House Sparrows did not change their declining trend after the increase of tree availability. Thus, the changes of tree cover were not related to House Sparrows decline (R2 = 0.12, F1,25 =3.54, P = 0.072). We suggest some alternative causes of the observed population decline related to predation, competition and agricultural management, especially the intensification of the use of land that could have decreased food availability during critical periods. In this way, from the end of the 80’s onwards there has been a decline of the number of groves ploughed together with an increase in the use of herbicides for weed control. These changes in weed management could have reduced the availability of bulbs and insects from May to September, a critical period for House Sparrows nesting in orange groves.