116 
 
 
ALDO LEOPOLD AND SARA ELIZABETH JONES 
 
 
remainder of April and May, June, and July. Dur- 
ing this 77 day period, all but 17 days were colder 
than normal. Normal temperatures did not reappear 
until August and September. There was no drouth 
to mask the effect of abnormal temperatures. 
  In short, 1945 was a "self-recording experiment" 
in which more than 50 animals and 100 plants at 
two stations registered their responses to a mid- 
April shift from warm to cold. Average dates for 
other years provide the "control." 
  During the early spring warm spell, migratory 
birds arrived earlier and earlier until the weather 
changed, at which time most birds were appearing 
5 to 15 days ahead of schedule. The onset of cold 
brought a rather prompt change to lateness; there 
were no early bird arrivals after May 1. The many 
species due during the first ten days of May were 
all from 2 to 14 days late. 
  In strong contrast to this prompt response of 
birds to the mid-April shift in temperature, plants 
responded much more slowly. No plants were late 
until mid-May, a month after the onset of cold. 
Maximum lateness did not develop until mid-June, 
two months after the onset of cold. The average 
curve for plants crosses the baseline 29 days later 
than the average curve for animals. Apparently the 
developmental mechanism in plants set in motion 
by the early warm spell gathered a momentum which 
expressed itself in early bloom through a month of 
ensuing cold. 
   So far 1945 phenology has been discussed in terms 
 of plants as a whole and animals as a whole. The 
 
 
Ecological Monographs 
       Vol. 1.7, No. 1 
 
 
behavior of particular species during the warm and 
cold periods will now be .considered. 
  Table 13 presents the items normally occurring 
during the warm period March 5 to April 13. These 
are classified by groups in a time sequence. It is 
apparent that the warm period produced the great- 
est earliness in forbs and woody plants, the least in 
birds and mammals, with lakes in an intermediate 
position. It is of some physiological interest that 
subterranean mammals like moles and spermophiles 
should have been early at all. The number of mam- 
mal items is, however, too small to be conclusive. 
  Table 14 is a condensed summary of the cold 
period, April 14 to July 27. The left hand number 
of each pair is the number of items early or late; 
the right (in parentheses) the average number of 
days early or late. It is apparent that earliness in 
birds and mammals ceased in mid-May, a month 
after the onset of cold weather, but that it persisted 
in some forbs into July. Woody plants, on the other 
hand, lost their momentum by the end of May. The 
impact of cold was very unequal as among species, 
as evidenced by the simultaneous existence of early 
and late groups, especially in forbs during late May, 
June and July. 
   It should be realized that some of the forbs per- 
 sisting in earliness long after the onset of cold were 
 still underground when the cold hit. Thus white 
 trillium [104] bloomed May 1 and April 15 at the 
 two stations, six and 20 days early. It did not 
 emerge from underground at the Sauk station until 
 April 14, a day after the cold began. In short, 
 momentum-earliness was in the root. 
 
 
TABLE 13. The Warm Period, March 5-April 13, 1945. 
 
 
      Birds 
Bluebird ..... - 6 
Meadowlark. . - 1 
Robin ........ - 2 
Killdeer ...... -15 
Grackle ...... -10 
Dove ........ - 6 
Woodcock.... - 4 
Fox sparrow.. - 6 
Cowbird ...... - 3 
 
Field sparrow. + 3 
Phoebe ....... -13 
Kingfisher.,.. -- 8 
Sapsucker. . . . - 4 
Hermit thrush - 15 
Purple martin. - 2 
Towhee ..... -13 
Cormorant.. . - 2 
 
 
    Mammals 
    Amphibians 
Woodchuck... - 1 
 
 
 
Chipmunk.... - 0 
Mole ......... -  8 
Leopard frog.. - 3 
 
 
Bat .......... - 15 
Cricket frog . . - 9 
Spermophile.. - 8 
 
 
Forbs 
 
 
Pasque..--18,-12 
 
 
Woody Plants 
 
 
Silver maple ..... 
        -8,-14 
 
 
 
 
Pussy willow. -13 
Hazel ....... -15 
Alder ....... -16 
Aspen ....... -18 
Forsythia.... --17 
Cottonwood . -22 
Elm. . .-19,-19 
 
 
    Lakes and 
      Rivers 
 
 
 
 
Wisconsin River. - 6 
Lake Wingra.... -10 
 
 
 
Lake Mendota. . - 12 
 
 
- 6 days - 6 days      -15 days           -14 days         - 9 days 
 
 
Normal Date 
March 5-15 
 
 
 
March 16-25 
 
 
 
 
March 26- 
  April 5 
 
 
 
 
April 6-13 
 
 
 
 
 
 
Average 
  earliness: 
 
 
-- 6 days 
 
 
-- 6 days 
 
 
--15 days 
 
 
- 14 days 
 
 
,- 9 days