Nestling Development of Jackdaws Corvus monedula in Agricultural Landscape

Abstract

Abstract A Jackdaw colony of over 200 nests, built in cavities of old willow trees along 3 km of a small road running through meadows next to the river Narew in an agricultural landscape (15 km southwest of Białystok, NE Poland), was studied to determine nest locations and construction, onset of egg laying, incubation period, egg parameters, clutch size and hatching success, nestling growth and mortality, breeding success as well as predation. The onset of laying and clutch size were correlated with ambient temperature and precipitation (p < 0.001). Hatching success was also determined by these environmental factors as well as by the degree of predation (p < 0,001). There was a statistically significant correlation between clutch size and hatching success (p < 0.001) as well as fledging success (p < 0.001). Nestlings hatching first or second grew faster, reached a higher body weight, and had a lower mortality rate than those hatching last or second to last. There was also a statistically significant correlation between nestling survival and clutch size as well as ambient temperature (p < 0.001 each). Nestling mortality caused by predators, i. e. mainly by martens Martes foina and domestic cats Felis domestica, was high in periods of intensive burning of the meadows surrounding the Jackdaw colony. However, mortality rate of the youngest nestlings was almost 100% lower in periods of high predation compared to times of low predatory activity. Several groups of insects constituted a high amount of nestling food, e. g. 60% of all Orthoptera occurring in the meadows next to the breeding colony. In that area the total dry body mass of phytophagous invertebrates amounted to 1.4-2.0 g per m2, of which 0.3 g were fed to the nestlings. The percentage of zoophagous invertebrates delivered to the offspring was high with about 30-35%. From an economical point of view, Jackdaws during the breeding season are advantageous in an agricultural landscape because they reduce pest insects significantly while consuming only an insignificant amount of all seeds applied.