THESES. GASTON DE GAAL. 



„A critical control of the data of migration is indispensable; the 

 mean figure is to be gained from the average data of several years' obser- 

 vations in a certain region". 



„Average figures— mathematical treatment — give a more accurate 

 result than mean figures— geometrical treatment". („Aquila" VII. 1900. 

 pp. 358, 359.) 



„As a foundation for working out comparative international mate- 

 rial on Bird-Migration the geographical-chronological method -zonal- 

 system — is most appropriate". („Aquila" IV. 1897. pp. 45-47.) 



Under the name of „Quadrat- System", this system is extensively 

 explained in: „Aquila" VII. 1900. pp. 13, 14, 371. 



„Between „extravillan"' and „intravillan" data there exists undoub- 

 tedly a temporal difference". („Aquila", taken from all registrations.) 



„Delay towards the North varies more or less, but can be proved 

 for every species from year to year". (Taken from all registrations.) 



,J\\& main-direction in the spring movement in Hungary is therefore 

 northerly. In certain parts however a deviation is observable,e. g. in the 

 case of the Stork (Ciconia ciconia), which in the eastern half of Hungary 

 moves from S. E. to N. W. — whereas in the big plain of the Alfold 

 and in the western part of the country the direction is from S. W. to 

 N. E.; the main direction however remains a northward one." („Aquila" 

 111. 1896. p. 69. and IV. 1897. p. 64.) 



„The assertion that migrating species, witlwiit exception, are obliged 

 to avoid high mountain-chains, has been refuted by the Hungarian 

 data" („Aquila" III. 1896. p. 74. - Since confirmed for Ciconia ciconia 

 and other species by Ertl.) 



„ln some species not the „first appearance", but the date of the arrival 

 of the main body — Culmination — gives a more uniform view of the 

 movement." („Aquila" III. 1896. pp. 60.61. Alauda arvensis). 



* „Extravillan" means the outskirts of a borough, „intravillan" the inhabited parts 

 of it ; the first has always earlier dates of arrival. 



oza 24 10! 



