Visual display of the Aldo Leopold papers : 9/25/10-6 : Writings

no larg or oonsistent differenoe between 1951 and the reoent average. The
do not seem worth inaludior in this p er, esvecially since there 1a no assurame

that the recorders were equally competent or adbared to aW uaiform standard.

A decade of dates of 329 seasonal events at two stations, 33 miles apart#

wre awlyzed wd omae with pr'ior records, 
Spin events during the decade 1935.'19415 were two weskit earlier than the
events at the same station in 161-M5, 
The northern station is tree days later in spriw  than the southern one,
*ioh i 
twice the epectation ner      6n     Law. Th   ditfference between the two
stations Is 
leset in early spri   and  eatest in mdi    r. 
The year-to yar variability of evets, as            with their 1wn aver es

tends to be greatest in .ar).y spriw, amd decreases progressively throu^
So= plants show little variability in date of first blooml they seem to be

governed more by 1Afth of daylight than by crrent weathero White clover,
the least 
variable plmt, has a st      dar doation of P.4 dys, which is only a third
of tha 
Peailing in other plants during the     m onth, 
Sm   birds show little variability in arrival date, despite the fact that
winter in or beyond the tr4os whore dhwaes in length of day are  oh les 
The least variable birds were rose-breasted grosbeak (3.1 days) and upland
plover (3.2 
days), both only a third of the deviation prevailing In other contemporary
Bird mirgration respond3 to cees in temerture much more qickly than the 
bloom of plants. In 1945 the   om    m of an early wa, period persisted in
thro   two moaths of subsequent cold.  This mmnt     caused early bloom in
trillim     dospite the fat that it was still   rr     ddring the warm period.

Duration of bloom in a cool dry June  as cmp.rdwith a hot wet June, was 
protracted 60 to 8)1 peroent in various groups of plante.