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Natural History of the Salamander,

Aneides hardii

The Sacramento Mountains Salamander, Aneides hardii (Taylor),
is a plethodontid of relict distribution in the spruce-fir vegetational
formation from 8500 to 9600 feet elevation in Otero and
Lincoln counties, New Mexico. The salamanders on which most
of this report is based were collected three, four, and six miles
northeast of Cloudcroft in the Sacramento Mountains. Additional
individuals were collected on the eastern slope of Sierra Blanca,
1.5 miles southwest of Monjeau Lookout, at about 9000 feet, Lincoln
County, and in the vicinity of Summit Springs and Koprian
Springs, 9300 feet, Capitan Mountains, Lincoln County. Certain
details concerning the populations in Lincoln County will be reported
elsewhere (Schad, Stewart, and Harrington, Canadian Jour.
Zool., in press).

We would like to thank Mmes. Donna Schad and Lora Lee
Johnston, Messrs. Robert Stewart, Frederick Harrington and Ralph
Raitt, and Dr. Robert Selander for assistance in the field, Dr.
W. Frank Blair and Dr. Marlowe Anderson for the use of specimens
in their care, and Dr. A. Byron Leonard for the identification
of the molluscan food items.

In the summer rainy season A. hardii lives in and under downed
timber and under talus accumulations. Occurrence, however,
seems to be partly subterranean and always local; seemingly good
habitat frequently appears to lack the animals. Our observations
and collections were made in July, August, and September in 1956,
1957, and 1958. Two hundred seventy-seven individuals were
taken; these were measured, sexed and examined for breeding
status. The food and parasite content of the guts of a few individuals
was determined. Thirteen salamanders were kept for varying
lengths of time in captivity. The specimens are now stored
in collections at New Mexico State University, University of Texas,
Museum of Vertebrate Zoology, and the Museum of Natural History,
University of Kansas.

The primary study and collecting sites were four and six miles
northeast of Cloudcroft, Otero County, at 8600 to 8800 feet in elevation.[Pg 576]
Vegetation was either almost pure stands of Englemann
spruce (Picea englemanni) or mixed stands of spruce, Douglas fir
(Pseudotsuga taxifolia) and white fir (Abies sp.). At each locality
small oaks (Quercus) were present among the dominant conifers.
Most of the salamanders found were in downed Douglas fir logs;
some were taken from spruce and others from cracks in a variety
of deadwood. In the less deteriorated logs the salamanders lived
under the loose bark or in small cracks and chambers near the
inner bark surface. In large fir logs in advanced stages of decomposition,
salamanders could be found to the very centers. This
kind of log was apparently highly favorable for salamanders, for it
was in such sites that we found notably large numbers of the animals
and most of the clutches of eggs that we collected; this kind
of log is not frequently found, for its wood is saturated with water
and completely punky and nearly ready for final collapse.

In winter, salamanders that spent the summer at the surface
presumably move to subterranean cavities, or, at least, to sites
away from winter freezing. In December, 1957, and April, 1958,
four feet of snow covered our collecting sites, and the downed logs
contained ice. A few logs were wet at the surfaces where sunlight
hit them, but just under such melt they were icy. On May 3, 1958,
snow was in isolated drifts and the centers of the logs were still
icy. On May 31, and June 22, 1958, there was no ice anywhere,
but no salamanders were evident. Late June is, however, around
the earliest time that A. hardii emerges (Taylor, 1941).

Food and Foraging Behavior

We identified the contents of stomachs from 16 salamanders
collected in 1956 and 1957; the items found in them are listed in
Table 1. It is not likely that this list is complete for prey species
because A. hardii eats a variety of food and probably takes prey
almost indiscriminately if it is of appropriate size. The kind of
food most frequently eaten was ants; they comprised almost 40
per cent of the total items. Nevertheless, less than half the stomachs
contained ants; this may mean that salamanders do not make
an effort to take ants over any other prey. Such foraging behavior
would result in random capture of ants, and it is noteworthy that
the frequency distribution of ants in stomachs suggests a Poisson
distribution, a mathematical description of one kind of random
distribution.

Table 1.—Numbers of Food Items Found in Stomachs of 16 Specimens
of Aneides hardii

Adult and larval beetles comprised about 28 per cent of the
total items, but were found in only seven of the stomachs. Beetles[Pg 577]
eaten were small representatives of beetle groups likely to occur
in or under logs. A relatively large species of spider was found in
nine stomachs; it represented only ten per cent of the items taken
but was one of the most important foods when mass is considered.

Two adult salamanders not included in Table 1 were found, in
the course of examination for parasites, to have empty stomachs.
One was a male, and the other was a female taken from a chamber
that held an egg cluster. It would not be surprising regularly to
find stomachs empty in "incubating" females, but the fact is that
the one other such female collected by us had a small amount of
food in the gut; probably these individuals take anything that enters
the egg chamber, but do not leave for active pursuit of food.

Foraging behavior of captive salamanders was observed by one
of us. The salamanders were maintained in a seven-gallon aquarium,
the floor of which was covered with soil, mosses, liverworts,
certain flowering plants, and pieces of rotten fir log. The salamanders
were placed in the terrarium in September, 1956, July, 1957,
and October, 1958; one individual lived 13 months, another 14
months.[Pg 578]

A variety of natural foods was present in the soil and plant matter
placed in the terrarium, and these were presumably eaten as
found by the salamanders. However, the great bulk of the food
used by the salamanders was introduced for them, in the form of
colonies of Drosophila melanogaster in half-pint milk bottles. We
tried to keep thriving colonies of flies, primarily of the mutant
vestigial-winged type, present in the terrarium; in 1957 this was
successful to the extent that there appeared to be a surplus of food
available at all times. We did not attempt to feed the salamanders
any wholly artificial food, such as ground beef.

Initially, the salamanders, although seemingly healthy and well-fed,
were not fat. Those that we maintained on a presumably
minimal diet remained slender and did not grow in length. Two
individuals captured in 1957, however, were maintained on food
in excess, and these grew in length and in girth; from an initial
size of about 37 mm. snout-vent length (a subadult size) they
attained about 45 mm. snout-vent length (an adult size) in a
period of five months. The observations on foraging behavior
were made primarily on these latter individuals.

The salamanders captured prey by pursuit. A salamander would
pursue a fly until it was caught, or until it moved out of the field
of action. The salamanders were attracted by movements of
flies, and ignored those that were completely quiet; predation was
oriented almost wholly on a visual basis. Once they were within
2 to 4 mm. of a fly they would snap out the tongue to secure the
fly; they were successful in capturing vestigial-winged flies in about
75 per cent of all tries. The relative success of capture was greater
when the animals were fresh from the field and less after they had
become fattened. The vigor of their pursuit also decreased noticeably
once they became fat. About two days after any new
fly colony was placed in the terrarium, a salamander would take
up a position just inside the lip of the milk bottle, which was placed
on its side. From this vantage point the salamanders took heavy
toll of the fly populations, eating both adults and larvae.

Initially the salamanders foraged indiscriminately in daylight or
in darkness. Later, as they became fat, they avoided high light
intensity and were active only at night or under artificial light of low
intensity. The latter pattern of activity is probably typical of the
pattern they maintain under natural conditions. Certainly we
never saw individuals abroad in daylight at Cloudcroft, yet under
favorable environmental conditions they were to be found in sites[Pg 579]
that required considerable movement over open areas of the
ground surface.

For several months two individuals of Eurycea longicauda were
kept in with A. hardii. Foraging of these two plethodontids is
nearly identical, but the tongue of an adult Eurycea can be extended
somewhat more than one-half inch in capturing flies; for
A. hardii this distance is usually less than one-quarter inch. The
relatively short tongue of A. hardii can be correlated with its life
in restricted, subsurface chambers, where prey most frequently is
close to salamanders; E. longicauda inhabits significantly more
open sites.

Parasites

Thirty of the adult Aneides collected were examined for parasites;
most were parasitized by two species of nematodes, Oswaldocruzia
sp. and Thelandros sp. The former is found in the anterior
part of the small intestine and occasionally in the stomach,
and the latter occurs in the rectum. There were no gross intestinal
pathological changes in the salamanders resulting from parasitism.
In fact, no pathological or structural abnormalities were noted in
any of the salamanders examined. We believe the two nematodes
are well-tolerated by the salamander.

Table 2.—Occurrence of Parasitic Nematodes in Aneides hardii

The numerical and temporal occurrence of the nematodes is
summarized in Table 2. It should be noted that of the 17 worms
constituting the maximum infection by Thelandros, only one was
an adult worm; the maximum number of adult Thelandros in any
one host was five. Similarly, the heaviest Oswaldocruzia infection,
15 worms, consisted of immature individuals; the maximum number
of adult worms in any one host was ten.

The monthly variation in the relative occurrence of young stages
versus adult in both nematodes (Table 2) suggests that the parasites[Pg 580]
are eliminated from hosts sometime in the long period, late
September to early June, when A. hardii exists subterraneously;
the worms thus would be reacquired annually when the salamanders
resumed living on the "surface" or near the surface. Table 2
shows that the majority of the worms are immature (100 per cent,
in Oswaldocruzia) in samples taken in July. Additionally, all but
one individual of those constituting the 20 per cent occurring as immature
Oswaldocruzia in the period August to September were actually
collected in early August. These were found in one salamander,
and this constituted the heaviest infection for the period; crowding
effects may have led to retardation of development of the worms.

If it is true that parasites are reacquired each spring—we assume
that no temperature factors or immune reactions are delaying
development of the worms, and no unusually long external ovic
or free-living phase is a necessary part of their life-history—then
the host-parasite data can be used as a basis for hypothesizing
about the winter life of the salamander. During "surface" life
the incidence of parasitism is high (90 per cent and 83 per cent:
see Table 2), indicating that salamanders are readily invaded in
times of activity. Salamanders examined in September were all
parasitized and probably carried nematodes with them into their
winter retreats. This part of their habitat should thus be contaminated
with infective stages of both parasites. Yet the salamanders
seem to become re-infected when the period of summer activity
starts (note the high incidence of immature parasites in
salamanders taken in July); therefore, the salamanders lose their
worms in winter. This suggests that during their subterranean
life salamanders are inactive, and avoid ingestion of infective stages
of the parasites. A fairly complete hibernation such as we suppose
they undergo has been reported by Szymanski (1914) for Salamandra
on the basis of kymographic records of movement.

Characteristics of Breeding

Sex-ratio

Tables 3 and 4 show the distribution of sexes for two subsections
of our sample. The ratio of males to females in the total sample
was nearly 1:1. There were differences in ratios between the
three general localities: the two northerly sites had fewer females
than males, when compared with the Cloudcroft samples. This
is true for the samples of adults, but not for the juveniles, where[Pg 581]
in each instance the females predominated. We cannot absolutely
explain these differences in ratios. Possibly the data on adults reflect
different patterns of activity among the sexes so that adult
females are simply not present in numbers where we looked for
them. They could be located underground, in connection with
"incubating" duties; if this is true it would account for the fact that
so few egg-clusters have been found in logs.

Table 3.—Sex Ratios in Aneides hardii, Total Sample

Table 4.—Sex Ratios in Aneides hardii, Adults

[Pg 582]

Age-ratio

The data in Table 5 show adult salamanders to outnumber
young at each collecting locality. This is probably not an accurate
reflection of actual age composition in this species. Yet, we obtained
the same general result in all three years of the study. We
assume, therefore, that young were located where we could not
catch many of them; probably they were underground. Sites of
hatching and of the activities of early life would thus occur where
we think the bulk of eggs are laid.

Table 5.—Age Ratios, Adults-juveniles

For purposes of this study we had only to age the individuals
into adult and subadult classes. The criterion for adult status was
breeding capability. A five-millimeter testis was the smallest size
found in individuals that probably bred, and all of these were 40
mm. or more in snout-vent length. We arbitrarily considered individuals
smaller than 40 mm. to be subadult. This probably does
injustice to reality (females were treated the same way), but it
should be noted that any error introduced in this way was almost
certain to have increased the number of "subadults" in the samples.
Thus, the hypothesis above based on age-ratios is not automatically
invalid because of improper aging.

Timing of the breeding season

The time in which egg-clusters are deposited is a good rough
index to events in the breeding cycle. We found four egg-clusters,
one on July 14, 1957, and three on July 27, 1957; the only other
eggs taken to date were found in late August (Lowe, 1950:94).
Thus, courtship could occur in June, oviposition in July and August,
and hatching from August to September. Actually, it is likely that
the season is more restricted in time for any one year. Lowe's find
was made in a year in which the summer rains were late, beginning
in late July (Stebbins, 1951:137), whereas ours were made in a
year having abundant and relatively early rainfall, beginning in
late June. Microclimatic humidity is of extreme importance to
both the salamanders and their food.

We suppose a great deal of breeding activity takes place underground;
the chronology of events in such sites may bear no close
relationship to those occurring at the surface, yet it is likely that a
close parallel would be found. Breeding activities are ordinarily
associated in time with greatest food abundance.[Pg 583]

Clutch-size

By clutch-size we refer to the number of eggs in laid clusters.
We collected clutches of six, four, four and one; adding one more
of three (Lowe, op. cit.) gives an average of 3.6 eggs per cluster;
the average is 4.2 eggs if our clutch of one is discarded on the
grounds it was incomplete.

For comparison we have listed (Table 6) clutch-sizes for some
other plethodontids. It should be noted that these numbers refer
only to eggs deposited in clusters, and not to large ovarian eggs.
Thus, Aneides hardii has the lowest range in clutch-size of any
North American plethodontid on record. It has been noted in
other species that low clutch-size is correlated with low productivity,
slow population turnover, and long average life-expectancy
(Lack, 1954:103-105; Pitelka and Johnston, MS). If this is the
case with this salamander, several other features in its environment
and habits would tend to reinforce such population structure:
the animals are exceedingly well-concealed (they were first
described only 17 years ago [Taylor, 1941]), apparently have few
natural enemies (one garter snake [Thamnophis] was collected
within the habitat of the salamander in three years), apparently
have few and benign parasites, and abundant and readily available
food.

Table 6.—Ranges and Mean Values of Clutch-sizes in Salamanders of
the North American Plethodontidae[1]

Eggs and "incubation"

Our information concerning eggs essentially duplicates that
already reported (see Stebbins, 1951). All egg clusters that we
found were in small chambers within decomposing fir logs. In
each instance the eggs were suspended from the roofs of the
chambers. The clutch of six eggs was a compact mass, and the
individual suspensory cables of the eggs were intertwined and
fused with one another. The clutches of four eggs, although they
too were compact clusters, had each suspensory pedicel distinct
from the others. The surface of the eggs was lightly moist, but
did not glisten with water, and each egg was completely free of
the others. The outer coat of jelly of the fresh eggs measured
about 6.4 by 5.7 mm. as they hung suspended; sizes were uniform
and no egg was notably smaller or larger than the others.

We attempted to keep eggs artificially, but mold destroyed them
after 12 days. We had difficulty keeping them wet without inundating
them, for the climate at Las Cruces, New Mexico, where
we kept the eggs, is exceedingly dry in summer. Until death,
embryos were active and responsive to disturbances around them.
This was at a time when the limb buds could not be detected and
when the external gills were evident only under close scrutiny.

Two times we found adult female salamanders in the chambers
with the egg clusters. The other two egg clutches seemingly had
no attendant adult, but our method of going through a log was such
that we could easily have alarmed any attendant animal well before
we found the eggs, allowing time for the adult to move away from
the eggs. We presume that incubation, so-called, in A. hardii is
similar to that found in other plethodontids (see, for example,
Gordon, 1952:683). Our findings on the conditions of the stomachs
of these attendant adults have been outlined above ("Food
and Foraging"). Our limited data suggest that only females are
found in chambers with eggs.

Summary

The montane relict plethodontid Aneides hardii was studied in
the field and laboratory in 1956-1958. Food items detected in a
small sample of stomachs are listed tabularly. Two roundworms
were found to parasitize the guts of the salamanders; the parasitism
looks to be benign. Subterranean winter inactivity is thought to be
an integral part of the salamanders' lives, and is suggested in part[Pg 585]
by the life cycles of the worms. Summer activity appears to occur
at the ground surface in logs and talus, and underground; the
latter site is suggested by certain ratios obtained in the samples,
showing adults to outnumber young and males to outnumber females.
The season for egg deposition seems to be in July and
August. Clutch-size is lower than for any other plethodontid on
record. "Incubation" of eggs apparently parallels that characteristic
of other plethodontids.

Literature Cited

Transmitted May 11, 1959.

Transcriber's Notes:

Changed "vestigal" to "vestigial" on page 578: vestigal-winged flies.

Changed "inmature" to "immature" in Table 2: nematodes that were inmature.

Changed "auomatically" to "automatically" on page 582: not auomatically
invalid.

Changed "Syzmanski" to "Szymanski" in Literature Cited on page 585.