xii INTRODUCTION. 
RESIDENTS are species which are found in some district or 
other of the county throughout the year, and therein breed 
annually. 
SUMMER VISITANTS are species which appear annually in 
the spring, remain through the summer for the purpose of rearing 
their young, and afterwards depart in the autumn. 
WINTER VISITANTS are species which appear annually in the 
autumn, and remain in more or less numbers throughout the 
winter, departing in the spring for their breeding haunts. 
PERIODICAL VISITANTS are species which are observed in the 
county only on their annual passage to and from their breeding 
haunts in spring or autumn or both. 
CasuAL VISITANTS are species whose appearance in the 
county is uncertain, but whose occurrence—they being resident in, 
or more or less regular visitants to, other parts of the British Isles 
—is not improbable, even though their visit may be very few 
and far between. 
ACCIDENTAL VISITANTS are mere waifs and strays—species 
whose geographical range renders their occurrence in Britain quite 
exceptional and more or less remarkable. 
These definitions have been carefully framed, and will, it is 
believed, be found applicable to all cases, A few general remarks 
upon them, illustrated by characteristic examples, desirable in 
order to make their meaning perfectly unmistakable, will be given 
in proceeding to analyse the Yorkshire fauna. 
