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Copeia, 1990(3), pp. 781-787
The Effects of Temperature and Precipitation on the Breeding Migration of the
Spotted Salamander (Ambystoma maculatum)
O.J. Sexton, C. Philips and J.E. Bramble
We examined and quantified the roles of air temperature, soil temperature and precipitation as
potential correlates of breeding immigration for a population of spotted salamanders in western St.
Louis County, Missouri, for 10 yr. Mean 3 d air temperature provided the best temperature predictor
of salamander immigration, significantly explaining 41% of the variation in the number of
immigrating salamanders up to the modal class. There was no relationship between the level of
immigration and the amount of precipitation recorded over a 24 h period spanning the movement of
salamanders. We describe favorable conditions of rainfall (4mm) and mean 3 d temperature (5.5 C)
above which 98.3% of all immigration occurred. After the first week of Feb., all days with these
threshold values showed some level of immigration. Salamanders did not immigrate during Dec. or
Jan. despite instances of above threshold temperature and precipitation. Male salamanders typically
are represented in greater frequency than females early in the immigration season. This difference
appears to be due to a differential response of the sexes to temperature. Salamander immigration was
significantly correlated with soil temperature at 30 cm below the surface. Most immigration occurred
when the soil temperature at 30 cm was at least 4.5 C and the thermal profile was reversed (the surface
was warmer than the soil at 30 cm). This threshold system of cues may reduce the likelihood that
immigrating salamanders will be incapacitated by sudden cold.
In 1930 F.N. Blanchard wrote a brief but insightful paper on the role that physical
factors play in initiating the breeding migration of the spotted salamander, Ambystoma
maculatum, in southern Michigan. He concluded that immigration began during the first
rain following the disappearance of the snow and the thawing of the ground surface.
Blanchard’s paper spawned a number of subsequent studies on the same topic but in
different locales: Pennsylvania (Baldauf, 1952), Indiana (Peckham and Dineen, 1954)
and Maryland (Hillis, 1977) and with other species of Ambystoma (Semlitsch, 1985;
Beneski et al., 1986).
The aim of our study in Missouri is to quantify the relationship between spotted
salamander immigration and environmental parameters such as air and soil temperature
and precipitation. The specific goals are to: 1) predict the conditions favoring
immigration in terms of air temperature and precipitation; 2) construct a statistical model
to predict the level of immigration based on these environmental correlates; and 3)
investigate the possibility that soil temperature (as opposed to air temperature) acts as the
proximal cue for the occurrence of salamander immigration either through a reversal in
the thermal profile of the soil or by the absolute temperature at some depth (e.g.,
hibernation depth). Sexton et al. (1986) and Phillips and Sexton (1989) have reported
upon other details of the breeding migration of the spotted salamanders at this locale.
LOCATION AND METHODS
The study site, Salamander Pond and the surrounding oak-hickory woodlands, is
located on the 800 ha Tyson Research Center of Washington University in western St.
Louis County, Missouri. This permanent pond has a maximum surface area of 350 m
2
and a maximum depth of 1m. Surface runoff supplies water; there is no outlet.

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We used a drift fence of 0.6 cm mesh hardware cloth to divert the immigrant
salamanders into drop cans (15 cm in diameter x 17cm deep) buried at 2m intervals along
the outer side of the fence. Depending on the year, the fence either completely
surrounded the pond or intercepted known migratory pathways. The cans were examined
for salamanders prior to the start of immigration until 7-14 d after emigration had ceased.
We checked the cans at least once daily during the migratory period. We recorded the
sex (except during the 1984-85 season) and total number of immigrants per day for the
winter-spring season s of 1977-80 and again from 1983-88, a total of 10 seasons. We
released captured animals on the opposite side of the fence.
To standardize for year to year variation in total number of immigrants captured
(variation more reflecting improvements in capture technique than actual variation in
population size), we analyzed the level of daily immigration as a frequency: (number of
immigrants per day)/ (total number of immigrants per season). When differences
between sexes were considered, males (or females) were expressed as a proportion of the
total number of individuals captured that date.
University personnel recorded daily precipitation and maximum and minimum air
temperatures at 0800 at a weather station within 150 m of the pond. We estimated mean
daily air temperatures by averaging maximum and minimum daily values. In addition to
mean, maximum and minimum daily air temperatures, we calculated running averages of
mean, maximum and minimum air temperatures for the 2-5 d preceding immigration
(e.g., mean 2 d, mean maximum 2 d, etc.).
We measured soil temperatures at depths of 1, 15, 30 and 60 cm between 1000-
1600 from Jan.-March of 1986-88. In 1980 and 1983 we measured soil temperatures
only at depths of 1 cm and 30 cm. The instruments used to measure soil temperature
(maximum-minimum thermometers, thermistor, and soil probes) were inserted into holes
drilled into the soil at locations adjacent to known migratory pathways within 100 m of
the pond. We collected data from 1 Dec. through the day of immigration by the modal
class for each relevant season. We sued linear and multiple regression to evaluate the
contributions of environmental cues to levels of salamander immigration (Sokal and
Rohlf, 1981; SAS Institute, 1982a, 1982b).
RESULTS
No salamanders immigrated during Dec.-Jan. For each of the 10 yr, a single
modal group of immigrants arrived at the pond between 23 Feb.-20 March and
encompassed between .50 and .85 of the total
immigrants for that season (Fig. 1). In addition,
there were 12 instances, spread over six of the
10 yr, in which smaller frequencies of
immigration (between .01-.26) occurred before
the movement of the modal class (Fig. 1). The
earliest date of immigration for the 10 seasons
was 2 Feb. (1986) when 14 males and one
female (.01 of total immigrants that season)
were collected in the cans. The mean date on
which the 10 modal classes of immigrants