A comprehensive survey of historical (pre-1936) Tasmanian newspapers was
undertaken, together with a review of museum and zoo records, to locate
articles or registry entries that cited female thylacines with offspring.
As the descriptions "pup", "young" and "cub" had been shown to be somewhat
elastic terms, only those reports and registry entries that were reliably
dated, and specified pouch occupancy, were collated..
breeding season of the thylacine showing mating period (red)
and period when females carry pouch young (purple)
(after Sleightholme & Campbell, 2014).
With one notable exception, these records show that females with pouch
young were caught or killed from the end of May (late autumn) to early
December (summer). The noted exception was a female with three pouch
young purchased by the City Park Zoo in Launceston shortly before 10th
April 1902 (Paddle, pers. comm. 26th March 2013). The records for
the month of December all refer to full-grown pouch young, which would
infer that the breeding season was drawing to a close.
With a gestation period estimated at around 28 days, mating would normally
occur from April to September. As the thylacine's prey species are
most abundant during spring and summer, this cycle is commensurate with
maximising food supplies for the young when they become independent of
the family unit the following year. No females with pouch young could
be located in the historical record between January (summer) and the early
part of April (autumn).
In Michael Sharland's regular "Peregrine" column, published in the
Mercury newspaper of the 29th October 1938 (p. 5), he makes the following
comments regarding the pouch period for marsupial young:
"Kangaroos and wallabies have young in the pouch through the Winter; the
Tasmanian devil carries its baby in its warm marsupial pouch till the Spring,
the 'tiger' does the same, although the last named is just as likely
to deposit its young ones in some sheltered nook while it is seeking food,
and tend to them there until they are large enough to fend on their own
Sharland's remark with respect to the thylacine is consistent with Sleightholme
& Campbell's historical findings. They conclude:
"A closer examination of Guiler's findings tells us little of when breeding
actually occurred, as the boundaries between pups, young and half-grown
are obscured by inconsistencies in the bounty data. The authors contend
that Guilers's original four-month estimate for the breeding season of
the thylacine was based on bounty data masked by bulk submission of skins,
hawking, and the questionable classification of young. We provide
an alternative hypothesis based on the historical record of females caught
or killed with pouch-dependent young. We fully acknowledge the limitations
of this small sample size, but contend that historical newspaper, museum,
and zoo accounts provide a more accurate survey of when breeding actually
occurred. These records show that the thylacine's mating season extended
from April through to September, with little evidence to support significant
out-of-phase breeding. Females with pouch-dependent young could normally
be found from May through to December, and with young at varying stages
of their development throughout the year. As such, a closed season
at the termination of the breeding cycle would have conferred little, if
any, protection to the species".
It is generally believed
that female thylacines reach sexual maturity between 2 - 3 years of age,
with males somewhat later at around 3+ years. By comparison, quolls (all
species) reach sexual maturity at 1 year (Anon. 2015) and the Tasmanian
Devil at around 2 years (Fox 2010), although with the advent of Devil Facial
Tumour Disease (DFTD), this appears to be reducing.
No historical observations
exist on the mating behaviour of thylacines either in the wild or captivity.
Sleightholme & Campbell
(2014) established that the mating season historically extended from April
through to September, with little evidence to support significant out-of-phase
D. Pemberton (1990)
noted with reference to one of the
nearest living relatives, the Tasmanian devil (Sarcophilus harrisii),
that reproductive success is high in
wild, non-diseased populations, with nearly all females of breeding age
(2 - 4 years old) bringing the full complement (n = 4) of pouched young
through to weaning. Although direct comparisons cannot always be
made, historical reports often cite female thylacines with their full contingent
of pups, which seems to indicate that the thylacine's reproductive success
is (or historically was) high in wild populations. The success
rate of weaned individuals reaching maturity however, is unknown.
Virtually nothing is
known regarding the incidence of pup mortality in thylacine litters.
The only reference that we have is that by a former trapper, Mr. G. E.
Randall of Hobart, in a letter addressed to the editor of the Mercury,
and published in the newspaper on the 12th December 1945 (p. 3):
"In regard to Mr
Stevenson's letter stating that the native tiger gives birth to four at
a litter - two males and two females - this is not the rule. I have
trapped within a radius of 25 miles from Burnie during 13 years (snaring)
15 tigers in one month. I have inspected their lairs and have at
times discovered one male and three females, and vice versa. Also
it happens that one is born dead or died shortly after birth".
It is unclear if Mr.
Randall is referring to the actual birth process when he refers to "born
dead or died shortly after birth" or the initial period of independence
from the pouch.
On the 3rd September
1902, a female
thylacine with three pouch young arrived at the National Zoological
Park in Washington, DC. One of the pups, a
female, died just nine days after its arrival at the zoo on the 12th September
1902, at the age of approximately 5 months. The cause of its death is unknown.