Possible non-offspring nursing in the southern right whale, Eubalaena australis

Abstract

During the austral winter, adult female southern right whales Eubalaena australis enter the South African coastal waters to give birth and raise their young. Most births take place over a 4-month period, when the females congregate in specific coastal areas or nursery grounds for up to a recorded maximum of 105 days. At this time, the density of cow-calf pairs in nursery areas can reach as high as 3.2 pairs/km2 over 26 km of coastline. Although a single young is born and suckled exclusively for 7 months to a year, recent observations on nursery grounds include 3 incidents where apparently abandoned/orphaned calves-of-the-year have been seen associating with a minimum of 2-3 different cow-calf pairs over periods of 11-38 days. Attempts to suckle from these females have been noted in 2 of the cases, with the response of the female varying from extreme avoidance to apparent tolerance. In one instance where the observations of the same trio extended over 21 days, the non-offspring appeared to compete at least equally with the offspring, even though the mother directed her evasive tactics more at the non-offspring than her own calf. At the same time, both of the calves exhibited some growth in length when compared with the size of the adult female: their subsequent survival is unknown. Non-offspring nursing in monotocous species is generally rare, and the costs to the female potentially high: this is certainly the case for seasonally feeding mysticetes such as the right whale, where the costs of lactation cannot be recovered until the cow resumes feeding about 4 months after parturition. Hence, it is perhaps not surprising that these are the first recorded observations of contemporaneous nursing attempts by offspring and non-offspring calves of any mysticete.

Full text

405
Possible non-offspring nursing in the southern right whale, Eubalaena
australis
Peter B. Best,* Simon H. Elwen, Per J. Palsbøll, Meredith Thornton, Evan Austin, and Katja Vinding
Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028,
South Africa (PBB, SHE, MT, KV)
Iziko South African Museum, P.O. Box 61, Cape Town 8000, South Africa (PBB, MT)
Marine Evolution and Conservation, Groningen Institute for Evolutionary Life Sciences, University of Groningen, Nijenborgh 7,
9747 AG Groningen, The Netherlands (PJP)
African Wings Aerial Whalewatching, P.O. Box 215, Hermanus 7200, South Africa (EA)
Statens Serum Institut, Artillerivej 5, 2300 Copenhagen S., Copenhagen, Denmark (KV)
* Correspondent: peter.best@axxess.co.za
During the austral winter, adult female southern right whales Eubalaena australis enter the South African coastal
waters to give birth and raise their young. Most births take place over a 4-month period, when the females
congregate in specific coastal areas or nursery grounds for up to a recorded maximum of 105 days. At this
time, the density of cow–calf pairs in nursery areas can reach as high as 3.2 pairs/km
2
over 26 km of coastline.
Although a single young is born and suckled exclusively for 7 months to a year, recent observations on nursery
grounds include 3 incidents where apparently abandoned/orphaned calves-of-the-year have been seen associating
with a minimum of 2–3 different cow–calf pairs over periods of 11–38 days. Attempts to suckle from these
females have been noted in 2 of the cases, with the response of the female varying from extreme avoidance to
apparent tolerance. In one instance where the observations of the same trio extended over 21 days, the non-
offspring appeared to compete at least equally with the offspring, even though the mother directed her evasive
tactics more at the non-offspring than her own calf. At the same time, both of the calves exhibited some growth
in length when compared with the size of the adult female: their subsequent survival is unknown. Non-offspring
nursing in monotocous species is generally rare, and the costs to the female potentially high: this is certainly the
case for seasonally feeding mysticetes such as the right whale, where the costs of lactation cannot be recovered
until the cow resumes feeding about 4 months after parturition. Hence, it is perhaps not surprising that these are
the first recorded observations of contemporaneous nursing attempts by offspring and non-offspring calves of
any mysticete.
Key words: Eubalaena australis, non-offspring, nursing, South Africa, southern right whale
© 2015 American Society of Mammalogists, www.mammalogy.org
Female southern right whales Eubalaena australis visit near-
shore waters along the South African coast between June and
December each year to give birth and raise their young. Most
births occur over a 4-month period between mid-June and mid-
October, with a peak in August (Best 1994). After giving birth,
females reside in these waters for up to 105 days nursing their
young, moving between favored nursery areas but only leav-
ing the coastline for higher latitudes once the calf has reached
a certain size (Best 2000). At this time each year, a number
of neonatal right whales strand on the South African coast,
approximately 15% are live when found (Best et al. 2001b):
the stranded calves are generally smaller than the calves seen
alive at sea, possibly because they are mainly first-born calves
(Best and Rüther 1992). Nevertheless, sightings of abandoned
calves at sea are rare, and the circumstances surrounding the
separation of mother and calf (and their subsequent behavior)
are unknown.
The length of lactation in southern right whales is not well
established. Some calves have been seen attempting to skim
feed next to their mothers at an estimated age of 6 months (Best
2007), while some females return to coastal nursery areas in the
following year with their yearling calf still in attendance: these
pairs apparently separate or disappear by about mid-August
(Thomas and Taber 1984; Best et al. 2003). If these latter
calves are still nursing, then lactation would have lasted about
12 months: Hamilton and Cooper (2010) have documented
Journal of Mammalogy, 96(2):405–416, 2015
DOI:10.1093/jmammal/gyv042

406 JOURNAL OF MAMMALOGY
mother–calf associations in North Atlantic whales lasting up to
14 months. Before separation, the yearling takes the initiative
in maintaining contact with its mother, nurses more frequently,
and appears to be obtaining as much nourishment as possible
before weaning (Taber and Thomas 1982). Some of these year-
lings then remain on the coast through September, October, and
November, where they socialize with adults and other subadults
(Taber and Thomas 1982; Thomas and Taber 1984).
Like most large whales, right whales normally give birth to a
single calf. Twin fetuses have been recorded in 0.5% of south-
ern right whale pregnancies (n = 220—Best 1994), but these
were relatively small (1.13 and 1.18 m long) and whether both
would have been carried to term or survived long after birth is
unknown. Documented observations of twin births or neonates
in right whales (i.e., with accompanying genetic evidence) are
unknown, and although killer whales Orcinus orca are said to
be the only cetacean species in which viable multiplets have
been recorded (Baird 2000), this assertion appears erroneous
(Ford and Ellis 1999).
Nevertheless, occasional sightings of southern right whales
accompanied by 2 calves have been reported along the South
African coast. Most of these observations of “twin” calves are
short term and opportunistic in nature, with little supporting
documentation in the form of photographs, etc. However, since
1997, there have been 3 occasions where the incidents have
been more protracted and the observations more fully docu-
mented. In this paper, we provide details of these 3 instances,
together with one at-sea observation of an interaction between
an adult female and an apparently abandoned calf, and attempt
to interpret the behaviors observed.
Materials and Methods
Annual aerial surveys along the south coast of South Africa
between Muizenberg and Plettenberg Bay (Fig. 1) were
undertaken in mid-October annually since 1979, their pur-
pose being photo-identification of all cow–calf pairs of right
whales seen. Methods used in field photography and subse-
quent laboratory matching of individuals have been provided
by Best (2011), but a relevant aspect of these surveys is that
they were wide in spatial extent but narrow in seasonal cover-
age. Currently (up to 2012), the Mammal Research Institute
(MRI) right whale catalog includes images of 1,318 adult
females and 599 of their calves that were conspicuously
marked dorsally (some of which also eventually appear in
the catalog as adults).
Fig. 1.—South African coastline showing localities mentioned in the text.

BEST ET AL.—NON-OFFSPRING NURSING IN RIGHT WHALES 407
From 1995 to 1997, a boat-based program of biopsy sam-
pling right whales was carried out annually between July and
November in the South African coastal waters, from Lamberts
Bay on the west coast to Wilderness on the south coast (Fig. 1).
In total, some 343 groups of right whales were intercepted
and 906 biopsy attempts made: details of the methods used
are given by Best et al. (2005). Individual identification pho-
tographs taken of each group intercepted were compared with
each other and where possible with the contemporary aerial
right whale catalog. Of relevance is that these surveys were
wide in both temporal and spatial coverage.
Since 2005, commercial whale-watching flights over Walker
Bay and the adjacent Pearly Beach area (Fig. 1) have been
undertaken on a daily basis during the whale season (approxi-
mately June to December), weather and tourist demand permit-
ting. Incidental photographs have been taken of groups seen
from a circling fixed-wing aircraft, both by the pilot (using a
Pentax K20D) and various passengers (including KV using a
Canon 40D with 200-mm lens or a 5D with 100–400-mm lens),
from a minimum altitude of 305 m as dictated by permit con-
ditions. Appropriate images have been cropped and compared
with the MRI catalog using the Hiby–Lovell matching system
(Hiby and Lovell 2001). These opportunistic data are obviously
circumscribed in spatial coverage but extensive seasonally: at
the same time, they are nonsystematic in nature so that only
whales of interest were photographed.
Nursing in right whales normally takes place with the mother
lying level at the surface. The calf commences suckling by arch-
ing its back and submerging, then turning in toward its mother’s
side. During suckling, the head remains beneath the mother’s
genital region, while the back is arched and the tail raised close
to the surface (sometimes with the tips of the flukes exposed):
suckling bouts last less than 1.5–4.5 min, depending on age
(Thomas and Taber 1984). Because the calf’s head is hidden
beneath its mother, it is essentially impossible to ascertain from
above-surface observations whether suckling is successful, so
in this paper, the term “suckling attempt” has been adopted for
occasions when the calf has adopted a typical suckling posture.
In boat-based observations, the duration of observations was
recorded as part of the normal protocol (as encounter time),
but in aerial observations was not. In annual aerial surveys the
duration of observations has been deduced (as a maximum)
from the time between the start of photography of successive
groups. In commercial whale-watching flights, durations were
derived from the time of the first and last frames as recorded
in the time stamp metadata associated with each photographic
image: where no photographs were taken there is no record of
the duration of observations. In the commercial whale-watch-
ing data, each daily flight was considered a separate encounter
(“observation”).
We have used photographic frames as instantaneous samples
of behavior, but have treated each photographic session as a
separate sample and expressed the incidence of a behavior as
the proportion of the number of frames in each session in which
it occurred. Because the photographs were taken ad libitum, we
have not attempted to calculate absolute rates of behavior but
only assumed that there was no selection for recording behavior
by the calf or non-offspring, so that the relative incidence of
behaviors shown by the 2 should be unbiased.
Relative measurements of calves against adults have been
made on the same image when both are at the surface with both
extremities visible and in the same approximate orientation,
after enlargement on a 55-cm monitor.
The distribution of observed ages at 1st parturition for 122
right whales off South Africa has been used to estimate a possi-
ble minimum age for mature females seen for the first time with
a calf. Although 1.6% of females have been observed with their
1st calf at age 5, animals at age 6 comprise 9% of observed ages
at 1st parturition. The latter age has therefore been selected as a
more appropriate minimum age.
Results
Case 1: interaction of near-term female with abandoned calf.—
On 10 July 1996, a lone adult right whale (A) was encoun-
tered at sea off De Hoop Nature Reserve (Fig. 1), travelling
west. Almost immediately thereafter a 2nd adult (B) was seen
approaching very fast from the west: the 2 animals joined up
and began traveling fast westward. Both animals, but especially
B, appeared highly agitated, with the head being thrust high
out of the water at each surfacing. After the boat closed with
the group, the whales reversed direction and began swimming
eastward. As the boat followed the group, a very small grayish
calf (C) was encountered, swimming slowly at the surface. At
that stage, both adults were about 100 m away from C. When
the boat stopped to inspect the calf, both adults approached.
Behavioral interactions between C and the adults then took
place, but the adults left without C following. The calf then
swam slowly round the boat, bumping it once, causing a large
piece of skin to become detached. The animal was clearly new-
born, with loose grayish skin indicative of an animal under-
going postnatal ecdysis that is completed on average within 1
week of birth (Reeb et al. 2005). The sex of the calf was deter-
mined genetically as female (Bérubé and Palsbøll 1996). The
boat then left C to follow the adults, which after moving about
200 m away reversed direction and returned to C. Whale B then
interacted quite strongly with the calf, surfacing right next to
it, and the calf began swimming alongside her in the normal
mother–calf position, with whale A also in attendance. Whale
B was biopsied and proved to be female. Shortly after B had
been biopsied, the calf was abandoned again, the adults moving
off several hundred meters. When the boat followed them, they
reversed direction and returned to C. When the boat approached
again, the adults swam off without the calf. This was the last
time that C was seen. Adult B continued to swim in an agitated
manner backward and forward, mainly inshore/offshore, some-
times accompanied by whale A. Eventually A and B separated,
causing loss of visual contact with whale A. Whale B was then
seen to associate with a smaller whale that possibly could have
been whale A. After biopsying the latter individual (determined
genetically to be male), the boat left the area. The total period
of observations was 1 h 44 min. It is possible that the observed

408 JOURNAL OF MAMMALOGY
behavior of the adults was influenced by the presence of the
boat, particularly following the biopsy darting of B.
Whale B was photographed again on 30 September 1996 off
De Hoop, about 7.5 nautical miles west of (and 82 days follow-
ing) its July location, with a calf (D). Both animals were biop-
sied, and the calf molecularly sexed as male. The cow was later
identified as MRI catalog number R99/11A, which had not
been seen previously in 17 annual surveys suggesting that D
was likely to have been its first recorded calf, making R99/11A
at least 6 years old in 1996.
Whales B and R99/11A had identical genotypes at 14 micro-
satellite loci, confirming that they were the same adult female:
R99/11A also shared at a minimum 1 allele at all 14 microsat-
ellite loci with calf D, confirming that it was its biological off-
spring. The microsatellite data from calves C and D, however,
proved these to be 2 different individuals, confirming the find-
ings from gender determination.
This incident can be characterized as an interaction between
a near-term female and an abandoned/orphaned non-offspring
neonate, in which the adult seemed to be the active partner, at
least briefly.
Case 2: association between lone calf and different mother–
calf pairs.—On 19 October 1997, during the annual photo-
graphic survey for right whales, a group consisting of a cow
and 2 apparent calves was encountered off De Hoop Nature
Reserve: one of the calves left the group almost as soon as
photography began but was relocated about 5 min later and
photographed on its own; the total duration of observations
was about 6 min. This was considered a highly unusual occur-
rence at the time, as usually a calf on its own will be rapidly
rejoined by its mother once the helicopter targets the calf for
photography. The cow was identified as MRI catalog number
R89/16A, a female first photographed with a calf in 1989 and
with subsequent calves in 1994 and 1997. Given a minimum
age at first parturition of 6 years, R89/16A was presumably at
least 14 years old in 1997. The lone calf was readily identifi-
able from a large white dorsal blaze and was assigned the MRI
catalog number R97/72c.
On 29 October 1997, the same calf was encountered at sea
off De Hoop about 2 km from the sighting 10 days earlier.
About 200 m away was another cow–calf pair, the adult of
which proved to be MRI catalog number R97/56A, a female
photographed for the first time with a calf (and so presumably
about 6 years old): it was photographed 3 years later with a 2nd
calf. All 3 animals were biopsied: the calf with the white blaze
was molecularly sexed as male and seemed in good condition.
The period of contact with the whole group lasted 25 min, dur-
ing which time no 2nd adult arrived to claim this calf.
Although no attempts at suckling were observed, this was
the first incident in which an apparently lone calf was observed
associating with different cow–calf pairs several days apart.
Case 3: attempted non-offspring nursing.—On 8 December
2012, a solitary calf was seen from the air off Pearly Beach
(Fig. 1): it did not seem to associate with any of several cow–
calf pairs in the bay. The next day a cow was seen off Pearly
Beach with 2 apparent calves in attendance. While 1 calf was
calmly swimming in the vicinity of the female, the other was
actively attempting to access the cow’s genital area. The cow
was twisting her body and attempting to avoid the second, very
persistent calf: observations continued for about 15 min before
the aircraft had to leave for passenger exchange. On a 2nd trip
the same day, 2 calves were observed together but no female
was seen in the vicinity.
Thereafter, a cow with 2 calves in apparent attendance was
seen 6 times between 16 December and 26 December in Walker
Bay, about 30 km to the NW of Pearly Beach (Table 1). On 4 of
these occasions, the cows involved could be photo-identified,
proving to be 3 different individuals:
R09/162A, first seen with a calf in 2009 and seen on 18
October 2012 during the aerial survey with a single calf
about 60 km to the southeast of Walker Bay; comparisons
of photographs showed that this calf was still present on
16 December;
R97/113A, seen with calves in 1997, 2000, 2003, 2006,
and 2009, and on the aerial survey on 4 November 2012
in Walker Bay as escort to a 2nd adult female (R86/09A)
with a calf;
R09/335A, first seen with a calf in 2009 and only photo-
graphed by the whale-watch operation in 2012, not by the
annual aerial survey that year.
Assuming these cows all had their 1st calf at a minimum age
of 6 years, they would have been at least 9, 21, and 9 years old,
respectively, in 2012.
One calf was photo-identified on 3 occasions (16, 21, and
26 December) as the same individual (E) and was observed
making suckling attempts on 2 different cows; if it was
assumed that it was the same non-offspring observed on all
occasions that year, then it was seen on 9 occasions, with
at least 3 different cows on 5 different days and alone on
one day (Table 1).
Evasive reactions by the mother were recorded 3 times on
2 different days. For example, when first encountered on 21
December, the cow R97/113A was lying in an area of white
water and disturbed substrate, interacting with E while its own
calf lay about 2 (adult) body lengths distant. E was attempting to
dive beneath the genital region of the cow, which responded by
lying on its back, a tactic sometimes used by mothers to termi-
nate nursing by their own calf (Thomas and Taber 1984). When
encountered 90 min later, the same cow was found still lying
on its back in a patch of disturbed water, with E attempting to
access its genital area (Fig. 2A). There was initially no sign of
the cow’s own calf, but after 2 min, E seemed to finish harassing
the cow and started to move away. The cow then rolled upright,
turned more than 90°, and headed inshore (Fig. 2B). Zooming
out, the camera showed that the cow was headed toward a 2nd
calf (Fig. 2C). Assuming the cow was about 14 m long (Best
and Rüther 1992), this 2nd calf is estimated to have been about
200 m distant from the cow at the time the interaction with E
ended. Given the time elapsed from the image time stamps, the
cow must have covered the intervening distance at a speed of
10.3 km/h, faster than any leg swimming speed recorded for

BEST ET AL.—NON-OFFSPRING NURSING IN RIGHT WHALES 409
362 right whale groups tracked by theodolite from the shore
(Barendse and Best 2014). Observations ceased after 6 min,
with the cow–calf pair swimming together and E following
them at an estimated distance of 95 m (Fig. 2D).
At other times (e.g., 26 December), the cow was not seen to
make any attempt to dissuade either calf from suckling in 8 min
of observations: rather the 2 calves dove beneath the female to
access the genital area, often from separate sides, and seemed
to be jostling for position.
To summarize, assuming only a single individual was
involved, an apparently abandoned or orphaned calf interacted
with at least 3 different mother–calf pairs over a period of
19 days. Apparent attempts to suckle by the non-offspring were
seen on 4 days and from at least 2 different mothers.
Table 1.—Observations of non-offspring involvement with cow–calf pairs of right whales (Eubalaena australis), South Africa, 2012, 2013: all
aerial sightings made from commercial whale-watching operation (sightings made on separate flights on the same day listed separately). Letter
codes are as follows: N = non-offspring, MC = mother + calf, MCN = mother + calf + non-offspring. ? = no photographs available for individual
identification.
Encounter no. Date Location Seen from Group type Identity of
non-offspring
Identity of
mother
Attempted
suckling by
Remarks
2012
1 8 Dec. Pearly Beach Air N ?
2 9 Dec. Pearly Beach Air MCN ? ? N Mother evasive to N
3 9 Dec. Pearly Beach Air CN ? ?
4 16 Dec. Walker Bay Air MCN ? ? C, N
5 16 Dec. Walker Bay Air MCN E R09/162A Trio relaxed
6 17 Dec. Walker Bay Air MCN ? ?
7 21 Dec. Walker Bay Air MCN ? R97/113A N Mother evasive to N, calf stands by—Fig. 2
8 21 Dec. Walker Bay Air MCN E R97/113A N Mother evasive to N, calf stands by—Fig. 2
9 26 Dec. Walker Bay Air MCN E R09/335A C, N Calves possibly competing for access
10 30 Dec. Walker Bay Air MC R97/113A No sign of N
2013
11 24 Nov. Pearly Beach Air MCN F R13/375A No sign of a cow without calf
12 24 Nov. Pearly Beach Air MCN F R13/375A
13 25 Nov. Pearly Beach Air N ?
14 25 Nov. Pearly Beach Air N ?
15 25 Nov. Pearly Beach Air MCN ? ? N Mother evasive to N, calf stands by
16 27 Nov. Pearly Beach Air MCN ? ? N Mother evasive to N
17 27 Nov. Pearly Beach Air MCN ? ?
18 28 Nov. Pearly Beach Air MCN ? ? N moving between c/c pairs, mothers
evasive
19 28 Nov. Pearly Beach Air MCN ? ? N moving between c/c pairs, mothers
evasive
20 28 Nov. Pearly Beach Air MCN ? ? N moving between c/c pairs, mothers
evasive
21 2 Dec. Pearly Beach Air N ? Further out in bay
22 2 Dec. Pearly Beach Air MCN F R13/376A N, C
23 2 Dec. Pearly Beach Air MCN F R13/376A N Calves possibly competing for access
24 2 Dec. Pearly Beach Air MCN F R13/376A N, C See Fig. 3
25 3 Dec. Pearly Beach Air N F Breaching. Only seen on 1 of 3 flights
26 4 Dec. Pearly Beach Air MCN ? ? N originally alone then joined MC
27 5 Dec. Pearly Beach Air N ?
28 8 Dec. Pearly Beach Air N ? In vicinity of 5 MCs
29 8 Dec. Pearly Beach Air N ? N Joined MC for 10 min, mother evasive
30 9 Dec. Pearly Beach Air MCN ? ? N Mother relaxed
31 11 Dec. Pearly Beach Air MCN F R91/55A N, C Simultaneous suckling attempts
32 13 Dec. Pearly Beach Air MCN F R91/55A N, C Alternate and simultaneous suckling
33 13 Dec. Pearly Beach Air MCN F R91/55A N, C Mother evasive initially
34 13 Dec. Pearly Beach Air MCN F R91/55A Mother relaxed
35 14 Dec. Pearly Beach Air MCN ? R91/55A N See Fig. 3
36 17 Dec. Pearly Beach Air MCN ? R91/55A N, C Simultaneous attempted suckling
37 19 Dec. Pearly Beach Shore MCN ? ? Mother evasive
38 19 Dec. Pearly Beach Air MCN F R91/55A C
39 20 Dec. Pearly Beach Air MCN ? R91/55A N (Mother recorded as evasive off camera)
40 21 Dec. Pearly Beach Air MCN F R91/55A Mother initially evasive
41 22 Dec. Pearly Beach Shore MCN ? ? Mother evasive
42 23 Dec. Pearly Beach Air MCN ? R91/55A N Mother evasive
43 30 Dec. Pearly Beach Air MCN F R91/55A N
44 30 Dec. Pearly Beach Air N ? ? N left behind by MC pair
45 31 Dec. Pearly Beach Air MCN F R91/55A N

410 JOURNAL OF MAMMALOGY
Case 4: attempted non-offspring nursing.—On 24 November
2013, an apparently lone calf (F) was spotted from the air close
to a mother–calf pair, in a bay to the east of Pearly Beach. From
the amount of sediment stirred up between them, it was inferred
that F had been trying to suckle from the cow. The pilot searched
the immediate vicinity and located a total of 12 mother–calf
pairs and the lone calf, but no unaccompanied adults. The situa-
tion was essentially unchanged on a 2nd flight 72 min later.
Thereafter a cow with 2 calves in apparent association was
encountered on 25 occasions on 17 different days in the Pearly
Beach area, over a total time period of 37 days (Table 1). In
total, 3 different cows were identified:
R13/375A, first seen with a calf in 2013;
R13/376A, first seen with a calf in 2013;
R91/55A, seen 5 times before on the South African coast:
in 1991 and 2007 as an escort to a cow–calf pair, in 2001
and 2009 as a single animal, and on 4 October 2013 as a
mother with a newborn calf, approximately 120 km (coast-
wise) to the east of Pearly Beach.
Fig. 2.—A) Female (Eubalaena australis) R97/113A lies on back evading intentions of non-offspring, B) leaves non-offspring to locate calf, C)
swims quickly and directly to calf, and D) swims off with calf with non-offspring following; Walker Bay, 21 December 2012.

BEST ET AL.—NON-OFFSPRING NURSING IN RIGHT WHALES 411
Assuming a minimum age at first parturition of 6 years, the first
2 females would have been about 6 years old. The minimum
age for R91/55A would be 22 years, but as it was recorded as an
“adult” when first seen a more realistic minimum age might be
25 years. Her calf in 2013 would have been at least 68 days old
when their first encounter with the non-offspring was recorded.
One calf was photo-identified on 14 occasions over 9 days
(24 November; 2, 3, 11, 13, 19, 21, 30, and 31 December) as
the same individual (F): on the remaining occasions, there were
no suitable images for matching. Suckling attempts by F were
seen on 8 occasions on 5 different days with 2 different cows
(Table 1). If it is assumed that the same non-offspring was
observed on all occasions, then it was seen on 27 occasions
on 18 days with 3 different cows: it was also recorded alone,
moving between, joining, or leaving cow–calf pairs on 11 occa-
sions, indicating considerable fluidity of association.
The reaction of the mothers varied, as with case 3. On 12 occa-
sions on 10 days, evasive behavior was recorded, probably involv-
ing at least 2 different mothers: the most common reaction was to
lie in an inverted position so that access to the mammary gland
area was denied. On 3 of these occasions, the behavior was only
temporary, and on another 5 occasions, the cow was recorded
as relaxed and/or permitted simultaneous or alternate suckling
attempts by the offspring and non-offspring calves (Table 1).
The observation of 31 December was the last of this group in
the area by both whale-watching boats and the aircraft. A flight
on 2 January 2014 found no whales at all along the coast within
20 km either side of Hermanus.
Assuming only a single individual was involved, this episode
can be characterized as an apparently abandoned or orphaned
calf interacting with at least 3 different cow–calf pairs over a
total period of 38 days, with the interactions being confined to
the same cow–calf pair over the last 21 days. Attempted suck-
ling by the non-offspring was photographically recorded on
10 days and noted on another 3 days and involved at least 3
different mothers.
Classification of non-offspring as calf or yearling.—Assign-
ment of juveniles as calves or yearlings has usually been based
on size. Taber and Thomas (1982) assigned calves-of-the-year
to 4 size categories: < 25% mother’s length, 25–50% moth-
er’s length, approximately 50% mother’s length, and > 50%
mother’s length. Although their size estimates were based on
the visible portion (from a 46-m cliff) of the calf during a nor-
mal surfacing relative to the overall length of the mother, and
so not completely comparable with the photographic method
used here, Best and Rüther (1992) provided photogrammet-
ric measurements which tentatively agreed with Taber and
Thomas’ classifications in that no calf exceeded 60% of its
mother’s length by mid-November. Taber and Thomas (1982)
defined yearlings as 75% of their mother’s length, while North
Atlantic right whales at 1 year of age reach 76% on average
of their asymptotic length (Fortune et al. 2012). Taking the
lower 99% confidence interval around the latter measurement
would suggest most yearlings would be at least 74% of their
asymptotic length. Assuming the asymptotic length is equiva-
lent to the average length of an adult female, these propor-
tions provide some criteria for distinguishing between calves
(< 60% mother’s length) and yearlings (> 74% mother’s
length) in the field.
Other meristic criteria that might be used to distinguish
calves from yearlings, such as relative head size or fluke width,
have not proved as reliable. Nine known yearlings on the South
African coast had head lengths ranging from 15% to 20.7%
of body length (average 17.2% ± 2%): this compared with an
average of 15.8% ± 0.9% in 115 calf measurements (Best and
Rüther 1992). Fluke widths could be estimated in 5 known
yearlings, ranging from 34.4% to 41.6% (average 38.1% ±
3.1%): fluke width in calves showed significant positive allom-
etry, increasing from 34.1% to 40.8% of body length over body
lengths of 3.41–8.5 m (Best and Rüther 1992). Thus, although
yearlings overall might have relatively larger heads and wider
flukes than calves, there was insufficient discriminatory power
in either case to make unequivocal assignments to age class.
Other nonmeristic criteria, such as head shape or callosity
development (Patrician et al. 2009), are less applicable for
aerial images and when taken late in the calving season (about
4 months after the mean date of birth).
Relative sizes of non-offspring and calves compared to the
accompanying adult are given in Table 2. They indicate that
all 3 non-offspring should be classified as size 4 calves and
Fig. 3.—Same non-offspring attempting to suckle from (upper)
R13/376A accompanied by calf (Eubalaena australis), 2 December
2013, and (lower) R91/55A accompanied by calf, 14 December 2013.

412 JOURNAL OF MAMMALOGY
5 of the accompanying calves would be either size 2 or size
4 calves. As all but one of the measurements were made in
December, or about 4 months after birth, these size classifica-
tions are consistent with the overall pattern of calf growth. In
the case of R97/72c, an inspection of the catalog of white-
blazed calves from the previous season failed to reveal a
match: as the efficiency of detecting calves on aerial surveys
from 1995 to 1997 was 71.4–76.9% (Brandão et al. 2011),
there seems a high probability that this individual was not
born the previous year.
Non-offspring F was subsequently matched with a calf
accompanying a cow photographed on 1 October 2013, approx-
imately 330 km coastwise to the east of Pearly Beach: from
its callosity development and cyamid infestation, the calf was
clearly recently born. This match would mean that F was at
least 55 days old when first seen attempting suckling from a
nonmaternal cow (and given the mean date of birth more likely
3–4 months old). The cow was R79/02A, previously seen with
a calf on the South African coast in 1979, 1981, 1984, 1990,
1993, 1999, and 2005: if 1979 was its first calving, then the
female would have been a minimum of 40 years old in 2013.
Discussion
These observations suggest that the individuals responsible for
the attempted non-offspring suckling in cases 2, 3, and espe-
cially 4 were all calves-of-the-year, rather than yearlings. In
cases 2 and 3, this conclusion is strongly dependent on their
relative sizes: if there are particularly diminutive or late-born
individuals, these might not fit the average growth curve and
could appear smaller as yearlings.
Although actual observations of suckling were not made
(and in any case are extremely difficult to detect, given that the
cow normally maintains its dorsal-up posture when nursing),
there seems little doubt that cases 2, 3, and 4 provide evidence
of a non-offspring attempting to associate with and/or suckle
from more than 1 (and up to at least 3) lactating females. In
cases 3 and 4, such interactions continued over 11–38 days, and
all 3 cases were confined to a limited geographic area.
Reactions of the adult females to the attempted suckling dif-
fered. Some seemed to tolerate the presence of a non-offspring
calf, to the extent that observers felt successful suckling by both
calves might have taken place. At the other extreme, R97/113A
(and the unknown female on 9 December 2012) reacted
violently, twisting and/or inverting the body (presumably to
prevent access to the mammary area by the non-offspring calf).
At such times, the cow’s offspring seemingly retreated tempo-
rarily to a safe distance from the fray. Reasons for the different
reactions are difficult to establish: in the case of R97/113A,
her calf was substantially smaller (and probably younger) than
those of other cows approached and for which the relative size
of the calf could be established, possibly eliciting a more pro-
tective response by the mother to preserve her milk resources.
An analysis of available photographic frames suggests that
the non-offspring calf may have been at least as competitive
as R91/55A’s calf for access to the genital area (Table 3).
During 11 encounters made over 10 days, the non-offspring
calf was photographed more often in a suckling position than
the mother’s calf on 7 occasions, an equal proportion of time
on 2 occasions and less often on 2 encounters; these propor-
tions do not reject the null hypothesis of equal access by both
calves (sign test, critical values for n = 9, P = 0.5, being 1 and
8). This excludes periods when the mother lay inverted prevent-
ing any suckling: R91/55A’s calf made no recorded suckling
attempts at all in the 3 encounters when this behavior occurred,
while the non-offspring calf was recorded in a potential suck-
ling position in 36–100% of the images. This would suggest
that the cow’s evasive tactics were directed mainly toward the
non-offspring calf.
It is difficult to conclude whether any of the non-off-
spring calves obtained sufficient nourishment from these
interactions to survive or even whether the survival of the
true calves was compromised. No stranded calves were
reported subsequently in the vicinity, but the conspicuously
marked R97/72c from case 2 has not been photographed on
15 subsequent aerial surveys (up to and including 2012).
However, these surveys were largely directed at cow–calf
pairs (and white-blazed animals can be of either sex—
Schaeff et al. 1999), and hence the absence of sightings can-
not be taken as unequivocal evidence of nonsurvival. There
was some evidence of growth in both the calves associated
with R91/55A. Even assuming the mother was 15.2 m long
(the upper 95% confidence interval for 57 adult females
measured photogrammetrically by Best and Rüther 1992),
the changes in proportion would correspond to overall
increases in length of about 15 cm for the calf and 30 cm
for the non-offspring over 19 and 17 days, respectively,
or 0.8 cm/day growth for the calf and 1.8 cm/day for the
Table 2.—Size of right whale Eubalaena australis calves and non-offspring relative to that of the mother, South Africa, with their classifica-
tions according to the criteria of Taber and Thomas (1982).
Date Non-offspring identity % Mother’s length Classified as Associated calf % Mother’s length Classified as
19 Oct. 1997 R97/72c < 60 Size 4 calf
16 Dec. 2012 E 53 Size 4 calf R09/162c 54 Size 4 calf
26 Dec. 2012 E 53 Size 4 calf R09/335c 57 Size 4 calf
30 Dec. 2012 E R97/113c 41 Size 2 calf
2 Dec. 2013 F 57 Size 4 calf R13/352c 51 Size 4 calf
11 Dec. 2013 F R91/55c 42 Size 2 calf
13 Dec. 2013 F 52 Size 4 calf R91/55c
30 Dec. 2013 F 54 Size 4 calf R91/55c 43 Size 2 calf

BEST ET AL.—NON-OFFSPRING NURSING IN RIGHT WHALES 413
non-offspring. These rates are well below that of 2.78 ± 0.71
cm/day recorded photogrammetrically for calves between
July and November by Best and Rüther (1992). If the mother
was indeed feeding both calves, then such impaired growth
would not be unexpected. Nevertheless, the data are limited
and the interpretations based on unproven assumptions.
In a review of non-offspring nursing in mammals, Packer et al.
(1992) have shown that in monotocous taxa such as Cetacea, it
is relatively more common where taxa form larger groups, it is
generally associated with “milk theft,” and it is also more com-
mon in taxa where a relatively high proportion of the behavior
involves females that have lost their own offspring. Although
baleen whales are not generally considered as particularly social
animals, with group sizes usually small (mean group size range
1–9) and impermanent (Whitehead and Mann 2000), southern
right whales are seasonally “social.” The females give birth in,
or bring their newly born calves into, coastal nursery areas, for
reasons that are not entirely clear but seem to include shelter
from swell, protection from predators, and possible avoidance of
males and other whales without calves (Elwen and Best 2004a,
2004b, 2004c). Such areas are consistent in location from year
to year and quite circumscribed in extent, so that cow–calf pairs
tend to aggregate within them. These aggregations can reach
very high densities: in 2012, for instance, 75 cow–calf pairs
were photographed along 26 km of coastline in the main nurs-
ery area off De Hoop, South Africa. As most pairs are within
about 0.9 km from the coast (Best 1990), this is equivalent to
an overall density of 3.2 pairs/km
2
. While such aggregations are
not strictly social units, as there is a constant flux of individu-
als, females tend to linger in these areas (Mate et al. 2011), with
average residence times estimated as 59 ± 3.9 days (Best 2000).
This provides plenty of opportunities for cow–calf pairs to inter-
act (and seems to meet Packer’s 1st criterion).
In this aspect, the nursery areas almost represent the ceta-
cean equivalents of pinniped rookeries, where adult females
congregate seasonally for parturition and early care of their
young. Within such rookeries, milk theft is often the most fre-
quent mode of non-offspring nursing, being recorded as such
by Packer et al. (1992) in 5 of the 7 species for which non-
offspring nursing was recorded (Arctocephalus galapagoensis,
Eumetopias jubatus, Zalophus californianus, Leptonychotes
weddellii, and Mirounga angustirostris). Given the similar jux-
taposition of cows with newborn calves in right whale nursery
areas, it is perhaps not surprising that instances of milk theft by
southern right whales should occur. Such instances are likely
uncommon, given that the 1997 observation of a lone calf was
the first in photography of 1,337 cow–calf pairs over 19 years
of surveys (acknowledging that milk theft by an unabandoned
calf would go undetected in such data). The recent occurrence
of instances in 2 successive years is intriguing but is most likely
an artifact reflecting greater observer awareness or coverage
(especially by commercial aerial whale-watching operations).
All the instances of potential non-offspring suckling
recorded to date seem to have been initiated by the calves
themselves, i.e., milk theft, rather than by females that have
lost a calf. Instances of the latter phenomenon might present
as a 2nd adult associating or interacting with a cow–calf pair
(as an “escort”). Between 2005 and 2012, there were 135 such
incidents recorded on aerial surveys, usually (84%) involving
a single individual but occasionally up to 6. In 71 (53%) of
the incidents, no photographs were taken of the escorts, pre-
sumably because they were only loosely associated with or left
the cow–calf pair before any frames could be exposed or were
deliberately not photographed as part of the survey protocol. In
the remaining 64 incidents, 43 involved individuals not photo-
graphed previously or subsequently (“new” individuals), while
Table 3.—Proportions of time spent in a suckling position versus at or on the surface for the right whale Eubalaena australis calves of
R13/376A and 91/55A and the associated non-offspring, as judged from successive photographic images, December 2013.
Date Duration of obs. (min) No. of frames Calf Non-offspring
Suckling Surface Suckling Surface
R13/376A
2 Dec. a ~3 18 33.3 66.7 44.4 55.6
2 Dec. b 8.3 41 4.9 95.1 92.7 7.3
2 Dec. c 10.5 57 42.1 57.9 24.6 75.4
R91/55A—in normal position
11 Dec. 9.6 50 66.7 33.3 95.7 4.3
13 Dec. a 4.9 23 87.0 13.0 78.3 21.7
13 Dec. b 5 28 28.6 71.4 85.7 14.3
14 Dec. 0.3 5 0 100 100 0
17 Dec. 1.4 26 100 0 100 0
19 Dec. 3.4 11 87.5 12.5 0 100
20 Dec. 2 7 0 100 100 0
21 Dec. 7.9 11 0 100 9.1 90.9
23 Dec. 3.7 3 0 100 0 100
30 Dec. 8 18 0 100 72.2 27.7
31 Dec. 11.5 42 7.1 92.9 40 60
R91/55A—in inverted position
13 Dec. b 5 10 0 100 100 0
21 Dec. 7.9 11 0 100 36.4 63.6
23 Dec. 3.7 24 0 100 100 0

414 JOURNAL OF MAMMALOGY
another 12 were photographed earlier or later but unaccompa-
nied by a calf, 2 of them on more than 1 occasion. Given the
nature of the catalog (targeted at cow–calf pairs), this lack of
resightings suggests that these individuals were either imma-
ture individuals of either sex or more likely males. In the other
9 cases, the “escort” had a previous or subsequent sighting his-
tory that included being seen with a calf, and so these were
most likely females. In 8 of these cases, the individual had
either last calved 3 years previously (n = 5) or calved 3 years
later (n = 2) or both (n = 1): as the modal calving interval in this
population is 3 years (Best et al. 2001a), this would suggest that
all of these escort females were in a potential calving year. The
absence of a calf could therefore imply that it was lost, unde-
tected, or still unborn: the 9th female “escort” was in fact seen
with a calf of its own later the same year. It is also possible that
there was a misclassification of the cow and its escort: aerial
contact with each group usually lasted only a few minutes and
if the calf moved between adults during this period, the iden-
tification of the true mother became somewhat subjective (3
of the 9 “cows” have never been seen with a calf on any other
occasion). The evidence is therefore somewhat inconclusive: a
few single females in their calving year associate with another
female and calf but the motivation for this association is unclear
and might include attempts to abduct the calf.
Cases of non-offspring nursing have been recorded in cap-
tive cetaceans, mainly bottlenose dolphins Tursiops trunca-
tus (Kasuya and Marsh 1984; Smolders 1988; Kastelein et al.
1990; Ridgway et al. 1995; Messinger et al. 1996; Gaspar
et al. 2000). In wild cetaceans, allomaternal care of offspring
has been proposed for schooling odontocetes such as sperm
whales Physeter macrocephalus (Best et al. 1984; Whitehead
and Weilgart 2000), and possible observations of a sperm whale
calf suckling from different females on different occasions, and
of 2 calves suckling from the same female, have been made
(Gordon 1987). In 1,679 h of observations, 3 instances were
recorded of bottlenose dolphin calves attempting to nurse from
nonmothers, 2 of which were immature females while the 3rd
was a female that had lost its calf 6 weeks earlier: these calves
never attempted to adopt an infant position with females with
dependent offspring (Mann and Smuts 1998). Although cases
of genuine adoption by a female that has lost its own calf are
difficult to detect, Frasier et al. (2010) describe an exchange of
calves between 2 adult female North Atlantic right whales on
the nursing ground within about 2 months of birth, with both
adopted calves surviving to reach maturity themselves. The
current observations of females permitting contemporaneous
suckling attempts by their own and non-offspring calves there-
fore seem to be the first for any mysticete.
As reviewed by Roulin (2002), several hypotheses (not nec-
essarily mutually exclusive) have been advanced to explain the
nursing of non-offspring in mammals in general. These include
(1) misdirected parental behavior, (2) reciprocity (with other
females), (3) kin selection (inclusive fitness), (4) milk evacu-
ation (surplus to needs), and (5) improving maternal skills. As
the current observations do not include any indication of recip-
rocal suckling, hypothesis (2) appears untenable. Estimates of
the minimum ages of 8 of the adult females involved ranged
from 6 to 25 (average 12) years, 4 of which were with their first
recorded calf. This makes hypothesis (5), of improving mater-
nal skills, unlikely, as it usually applies to virgin females that
spontaneously lactate, and is unlikely to apply in the instance
where the cow nurses non-offspring along with her own (Roulin
2002). Unfortunately, we do not know the extent of relatedness
of any of the females to the non-offspring calves: attempts to
match R91/55A to 3 of the 4 calves produced by R79/02A (the
mother of non-offspring F) from 1979 to 1990 were unsuc-
cessful and the 4th was unmatchable, so although we cannot
disprove that R91/55A and F were related the likelihood of
hypothesis (3) is reduced in this case. The current observations
do not allow us to discriminate between the remaining hypoth-
eses (1) and (4). Thus, a female that seems to tolerate a non-
offspring suckling is consistent with both misdirected parental
care and milk evacuation (if she has an abundant milk supply),
while we are uncertain whether the degree of toleration is influ-
enced by the relatedness of the non-offspring calf.
The case of R91/55A is especially interesting in that it
appears to be the only 1 of the 6 incidents where the recorded
association with a non-offspring extended beyond a day. Less
comprehensive photographic coverage of some of the earlier
incidents, where an extended association with a particular cow
may have been missed, may have contributed to this apparent
difference, although the maximum possible periods of asso-
ciation in 2 instances where a switch between mothers was
recorded could only have been 4 and 8 days compared to at
least 21 days in the case of R91/55A. The fact that R91/55A
had not been seen with a calf since its first sighting (as an appar-
ent adult) 22 years earlier might suggest that she was in better
physical condition than other adult females that had calved at
much shorter intervals, and thus more capable of simultane-
ously suckling 2 calves. However, her possible failure to be
spotted with a calf earlier might reflect a different reproductive
strategy (calving later than the aerial surveys or calving out-
side the survey area) or success (early loss or abandonment of
calves): it is interesting that this female was seen in 2 previous
years as an “escort” to another mother–calf pair. It should also
be borne in mind that these observations occurred late in the
season for right whales on the South African south coast (Best
and Scott 1993), and dwindling numbers of cow–calf pairs in
the area may have reduced options for the non-offspring to
switch to another mother.
As Packer et al. (1992) point out, non-offspring nursing
in monotocous species is generally rare, and the costs to the
female potentially high (from either simultaneous or sequential
suckling of 2 calves, for instance). This is certainly the case in
seasonally feeding mysticetes such as the right whale, where
the costs of lactation cannot be recovered until the cow resumes
feeding about 4 months after parturition: comparison of blub-
ber thickness between pre-pregnant and late lactating females
indicates a loss of 25% of the blubber layer over this period
(Miller et al. 2011). Hence, it will be especially interesting to
monitor the future calving histories of those females identified
in non-offspring associations in this paper.

BEST ET AL.—NON-OFFSPRING NURSING IN RIGHT WHALES 415
Acknowledgments
We are indebted to a number of colleagues who assisted with
these observations: J. Barendse, D. Reeb, M. Trolle, Wei-Lun
Chang, J. Karnik, A. Lagomarsino, D. Kervick, and K. Van der
Westhuizen. Helpful comments were made by 2 reviewers that
improved the paper. This work was supported through Grant
#68777 awarded to PBB by the National Research Foundation,
South Africa. The 2012 aerial survey was funded by the
International Whaling Commission and the 2013 survey by the
Petroleum Oil and Gas Corporation of South Africa Limited
(PetroSA).
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Submitted 8 June 2014. Accepted 8 October 2014.
Associate Editor was Jeanette A. Thomas.