@article{sparks_are_european_1999, 
author={Sparks, T. and Heyen, H. and Braslavska, O. and Lehikoinen, E.},
title={Are European birds migrating earlier?},
year={1999},
journal = {BTO News (British Trust for Ornithology)},
volume = {223},
pages = {8 - 9},
note = {Sparks, T.; Heyen, H.; Braslavska, O.; Lehikoinen, E.: Are European birds migrating earlier?. In: BTO News (British Trust for Ornithology). Vol. 223 (1999) 8 - 9.}}