AN EXPERIMENTAL EVALUATION OF THE CRITERIA
USED TO DISTINGUISH OWEDEPOSITED BONE IN
ARCHAEOLOGICAL CAVE DEPOSITS IN AUSTRALIA
Brendan Marehall
INTRODUCTION
Owls have ,been reported as contributors t o t h e fauna from many archaeological cave
deposits in Australia, e.g. Devil's Lair (Dortch and Merrilees 1971:112), Cloggs Cave
(Hope 1973:6), Cave Bay Cave (Bowdler 1979:163) and Koonalda C a v e (Thorne
1971:46). In the absence of owl skeletal remains or regurgitated pellets a number of
criteria have been used to establish whether a n archaeological bone assemblage is
owl-related, t o identify the particular species responsible, and t o distinguish owlintroduced fauna from that introduced by other agents of bone accumulation. These
criteria relate t o the number, size range, age structure of species represented, a n d t h e
physical condition of the bone. Concerning t h e latter, it has been suggested t h a t t h e
bone representing the prey of owls, especially t h e skull, will show little or no damage
(Archer and Baynes 1972:86; Hope 1973:5; Lundelius 1966:175).
Towards an evaluation of this criterion a n experimental analysis following a
procedure designed by Dodson and Wexlar (1979) was initiated. Its a i m was t o
formulate quantitative predictions concerning the type, relative amount and
condition of the bone of a given mammalian prey size likely t o be deposited by
particular species of owls. T h e analysis involved feeding two of t h e three species of
owl which are known t o roost in caves, the barn owl (Tyto alba) and the boobook owl
(Ninoz boobook), on a diet of house mice (Mus musculus). T h e regurgitated pellets
were collected and their skeletal contents recorded. T h e results of this analysis a r e
reported here and include a detailed description of the condition of the recovered M.
musrulus elements. They are interpreted with reference to t h e results of similar
studies, and discussed in light of the behavioural factors which influence t h e
represent at ion of regurgitated bone.
T h e results of this analysis d o support the contention t h a t bone derived from owl
,
pellets will be relatively intact. However, the occurrence of damaged M. musculus
elements suggests t h a t the condition of pellet bone is more variable than previously
thought, a n d several predictions are presented as a partial alternative to the
'undamaged' criterion. It should be emphasised that these predictions are based on
the condition of the bone of a single prey from the pellets of only two species of owl.
Importantly, bone from the pellets of the largest cave-roosting owl, t h e masked owl
(Tyto nouaehollandiae), w a s not inciuded and therefore the condition of bone
representing t h e prey of t,his owl remains unknown. For these reasons the analysis is
not, by any means, a complete evaluation of the 'undamaged' criterion and the
resultant predictions a r e not a characterisation of the bone representing all prey of
this predator type.
Those criteria relating t o the size and age range of prey are evaluated in light of the
diet of the three species of owl involved. It is suggested that while these criteria do in
fact characterise the prey of these owls, they are not specific enough for the purpose
of identifying owl-deposited bone in assemblages which also represent the activities of
other predators.
This paper begins with a brief account of t h e behaviour of the three species of owl
most likely t o roost in caves and therefore contribute bone via pellets to
archaeological assemblages.
THE CAVE-ROOSTING OWLS
.4t least three of the eight species of owl t h a t inhabit Australia are known t o roost in
caves. These a r e the barn owl (Tyto alba), the boobook owl (Ninox boobook), and the
masked owl (Tyto novaehollandiae). Due t o a lack of captive T. nouaehollandiae,
only T. alba and N. boobook pellets were available for analysis. All species can be
considered, however, in reference to the criteria concerning the size range and age
structure of prey.
The barn owl (Qto a l k )
T. alba is common throughout most of the mainland, occurring less frequently in
desert regions and Tasmania (Schodde and Mason 1980:78). The) are nomadic, one
individual reported]) having travelled 250 km in two months (Purchase 1972:75), and
breed opportunistically when prey, particularly rodents, become locally abundant
(Schodde and Mason 1980:78). This owl usually avoids dense or closed forest types,
and hunting can occur u p t o 10 km away from a roosting site (Schodde and Mason
1980:78).
T. alba will hunt while on the wing or, to conserve energy when food is in short
supply, from a perching position (Schodde and >!ason 1980:81: Flea) 1968:106). It is
a selective predator (see Morton 1975; Morton et al. 1977: Morton and $¶artin 1979),
preferring small terrestrial mammals i.e. native and introduced rodents (Rattus,
Pseudomys and .'Votornys), and marsupials ( 4nterhinus. Das yurcndes, I s d o n ,
S m i n t h o p s i s and Planigale). However. birds. lizards. frogs and insects are also taken
(Schodde and Idason 1980:81: Fleaj 1968:106). Prej is usuallj ingested at a feeding
perch but large carcasses may be taken back to a roost and eaten piecemeal during
t h e day (Schodde and Ilason 1980:81: F l e a 1968:106).
T. alba typically roosts in hollows in eucalypt trees but also uses tree branches in
dense foliage, holes in cliff faces, and suitable perches in mine shafts and European
dwellings (Schodde and Mason 1980:78). Fleay (1968: 101), Calaby (1969: 139) and
Schodde and Mason (1980:78) all note the use of caves by T. alba, and this behaviour
is considered to be relatively common (Hamilton-Smith pers. comm.).
The boobook owl (Ninoz boobook)
N . boobook is the smallest of the Australian owls.
While occurring in most
environments throughout the mainland and Tasmania, open eucalypt forest is the
preferred habitat type (Schodde and Mason 1980:53). Unlike T. alba adult birds are
territorial, particularly during the breeding season. Foraging territories will contain
a number of pre-selected roosting sites which may be visited for a period of u p t o
several weeks (Schodde and Mason l980:54).
Although insects constitute much of their diet, RT. boobook will also prey on small
native rodents (Pseudomys) and marsupials (Antechinus, Sminthopsis). Small birds
such a s parrots, quail and bats are also taken (Schodde and Mason 1980:54; Dwyer
1966:32). Ground-dwelling prey is located from a perching position and carcasses are
consumed a t the location of the kill or back a t a perch (Schodde and Mason 1980:53,
54). Tree branches provide the typical roosting site, but like T. alba they will use a
number of alternatives including rocky clefts and tree hollows (Schodde and Mason
1980:53).
Cave-roosting by N. boobook is mentioned by Fleay (1968:85) and Calaby (1969:139).
Observations are provided by Wakefield (1964:277) who flushed out an individual
from Flowerpot Cave in southwestern Victoria, and inferential evidence is supplied
by Hall (1975:35, 37) who reports on primary wing feathers attributed t o N. boobook
a t Marble Arch in New South Wales.
The masked owl ( Q t o novaehdlandiae)
T. novaehollandiae is the largest member of the Tyto genus, the Tasmanian variety
T. n. castanops reaching up t o 59 cm in length (Schodde and Mason 1980:70; also see
Fleay 1949:169). On the mainland it is sparsely distributed and restricted t o t h e
coastal basins but is relatively common in Tasmania. While dense eucalypt forest is
the typical nesting and roosting habitat, T. novaehollandiae hunts in open woodland,
forest margins and over clearings (Schodde and Mason 1980:70). It is relatively
sedentary and pairs will occupy a defined foraging range reaching up t o 1000 h a in
eastern Australia, covering a number of different habitat types. Several pre-selected
roosting sites are situated throughout a range and these will be used in rotation
(Schodde and Mason 1980:73).
The diet of T. nouaehdlandtae contains the small mammal prey of T. albrr and N.
boobook but also includes larger native genera such as Trtchosurus, Pseudocheirus,
Macrotis, Perameles and Bettongia (Schodde and Mason 1980:73; Fleay 1949:169).
Like T. alba. T. nuuaehdlandtae will hunt while on the wing o r by a post-pounce
method. Small prey will be consumed at a perching site while carcasses t h a t a r e too
heavy t o carry will be dismembered and ingested a t the location of the kill. Roosting
may occur in a number of places including tree hollows, clefts or ledges in cliff faces
and sink-holes, and less frequently, branches in dense foliage (Schodde and Mason
l980:73).
T h e use of caves by T. nouaehollandiae is noted by Fleay (1968:112), Calaby
(1969: l4O), Schodde and Mason (1980:73) and Hamilton-Smith (1965: 157). McKean
(1963:263) encountered a n individual in Clogg's Cave, eastern Victoria. Due to the
lack of additional observations and t h e absence of pellets, he considered t h a t this
particular bird was not habitually using the cave as a roosting place (McKean 1963).
T h e Nullarbor variety T. n. troughtoni, was designated a sub-species because of its
cave-dwelling habits. There have been no confirmed reports of live individuals since
t h e 1930s (Schodde and Mason 1980:70; Hamilton-Smi t h 1965:153).
In summary, each of the three species concentrates hunting activities in open habitat.
T h e mode in which prey is captured and consumed is variable, depending in part on
size a n d availability. While small mammals will be swallowed whole, the amount of
pre-ingestive manipulation can be considerable (e.g. see Fleay 1968:90). Large
mammals will be dismembered and eaten piecemeal while still on the ground or back
a t a perch. A number of pre-selected roosting sites will be situated throughout a
territory or range a n d , with their re-use, pellets t h a t are cast during t h e day will tend
t o accumulate.
Cave-roosting by individual owls of each of these species is probably habitual
(Hamilton-Smith pers. comrn.). Although daylight avoidance is the prime reason for
cave occupancy this behaviour may be partly due to the ready accessibility of
suitable prey such a s bats and rodents (Hamilton-Smith 1965: 152). T h e roosting site
is a ledge near the immediate entrance or twilight zone; owls are not known to enter
t h e dark zone of caves (Hamilton-Smit h 1965: 152).
ANALYTICAL PROCEDURE
T. alba and N. boobook were represented by small captive populations of five and four
individuals respectively, housed separately a t the Royal Melbourne Zoo. Both species
were fed a diet of house mice ( M u s musculus). The regurgitated pellets were
collected for 30 days, and after drying, these were individually measured and
weighed. T h e sample of 21 T. alba pellets and 20 AT. boobook pellets from which bone
w a s recorded, represents approximately 20% of the total collected over the 30 day
period a n d the range of weight values for whole pellets from each species. These
pellets were soaked in water for 30 minutes and their contents manually removed
under a n illuminated magnifying lens. T h e furry matrix was dried and examined
again for additional bone before being weighed.
T h e skeletal material was sorted by anatomical class and counted. To establish the
type and amount of whole bones completely digested, the minimum number of M.
m u s c u l u s individuals, a s suggested by the element with the highest relative frequency
after pairing, was estimated. The potential number of each element was then
compared to the numbers actually present. Up to 22 different bone types could be
identified. However, due t o their small size, ribs and most metapodials were not
considered further after noting their presence.
T o document accurately the location and extent of mechanical damage, the
osteological features of each of the 12 largest elements as defined by Cook (1965),
were numerically coded and assigned a relative percentage value of the element. In
this analysis, damage was defined as any macroscopically observable alteration from
complete bone as indicated by reference M. musculus skeletons. When possible, a
distinction was made between units that had become disarticulated but whose
components were still present, and the partial digestion of such units.
OBSERVATIONS ON THE PELLETS
The T. alba pellets varied from rectangular t o oval in shape and were often
attenuated at one end. Their mucosa coating, a characteristic of the Tytonidae
family (Fleay 1968:105), created a hard surface skin when dried. This coating
increases their potential for preservation (Schodde and Mason 1980:37) and has been
used t o identify pellets in a depositional context (see Hall 1975~37; Wakefield
1960:232). In comparison the N. boobook pellets were generally much smaller and
varied bet,ween rectangular to roughly circular in shape. Like all Nanoz pellets their
surface texture was coarse (Schodde and Mason 1980:37) and the furry matrix would
readily fragment when dry.
The digestion of cartilage by T. alba w a s often incomplete; caudal bones and
metapodials frequently remained artir111at~dand in one pellet the femora were still
attached to the pelvic acetabula. Excluding the minute pieces of bone, most of the
skeletal material could be identified. In contrast, two of the 20 N. boobook pellets
contained no bone whatsoever i.e. they consisted of fur only. When present, the bone
was usually more fragmented and many of the smaller pieces were beyond
identification.
For T. alba, variable pellet weight was a result of the differences in the number of M.
musculus individuals being represented, this ranging between 1-3. The mean weight
of the 21 pellets, all of which contained bone, was 1.8 gm. Skeletal remains
comprised over 60% of this weight. For N. boobook, differences in pellet weight were
more a result of variable degrees of skeletal digestion. The mean weight of the 20
pellets was 0.54 gm, less than half of which constituted M. musculus skeletal
remains.
THE RESULTS
M u s musculus skeletal remains
The results of the documentation of the A4. musculus skeletal remains from the
pellets of both species are recorded in Tables 1-4. The representation of elements
(Table 1) and the proportion that remained intact (Table 2) is summarised below.
Observed o r
a c t u a l no.
I n pellets
Ta
Nb
El ement
Crania
Mandibles
Clavicles
Scapul ae
Humeri
U1nae
Radi i
Pelves
Femora
Tibiae
F i b u l ae
Sacra
Sub-total
Expected
no. based
on the MNI
X o f units
present
Ta
Nb
24
48
24
50
49
48
47
46
47
49
47
16
495
15
13
4
10
11
12
11
12
17
10
7
2
124
96
96
48
100
98
96
92
94
98
94
64
90
100
43
13
33
37
40
37
40
57
33
23
13
38
Sternebra
Astragal us
Cal canea
Vertebrae
Sub-total
43
50
46
1192
1331
1
3
2
134
140
34
100
92
88
85
1
l0
7
17
15
Total
1826
264
86
21
94
T a = Tyt o alba
Nb = .%nor boobook
Table 1
The representation of M u s musculus skeletal remains from
boobook pellets. For T. alba the
minimum number of M. tnusculus individuals is 25 based
on scapula. For N. boobook the minimum number of M. musculus
individuals is 15 based on crania. Percentage present is the
pellet number relative to the MNI number
Tyto alba and N i n o x
Element
Total
no.
Tyto a l b a
No.
damaged
X
N inox boobook
Total
No.
no,
damaged
X
Crani a
Mand ib l es
Clavicles
Scapul ae
Humeri
U1nae
Radi i
Pelves
Femora
T i b i ae
Fibulae
Sacra
Tot a1
Table 2
495
233
47
124
121
98
The frequency of damaged M u s musculus skeletal elements
from the pellets of T y t o alba and .Vinoz boobook
No.
damaged
Ulnae (n = 48)
Proximal
Shaft
D1 s t a l
Total
Table 3
1
4
6
1
Humeri (n = 49)
Proximal
29
Del t o i d
6
Shaft
1
Di s t a l
0
Total
36
Scapulae (n = 50)
B1ade
44
Spine
26
Total
70
Clavicles (n = 24)
Proximal
7
D1s t a l
4
Total
11
Mandibles (n = 48)
Front
7
Back
7
Total
14
Crania (n = 24)
Nasal
20
Frontal
5
Parietal
24
Occlpi t a l
24
Total
73
Area
X
X
2
2
0
0
No.
damaged
5
3
0
8
Fibulae (n = 47)
Proximal
Shaft
Distal
Total
Sacra (n = 16)
Posterior
Anterior
Total
29
0
1
30
13
2
11
l
Tibiae (n = 49)
Proximal
Shaft
Distal
Total
6
21
28
47)
Femora (n
Proxi mal
Shaft
Distal
Total
-
Pelves (n = 46)
33
I 1l u n
Acetabulum
0
Ischiurn
ll
6
Pubi S
Total
50
Radii (n 47)
Prox imal
Shaft
D1s t a l
Total
Area
X
The frequency of damaged and intact areas on Mu8 muaculus
skeletal remains from Tyto alba pellets
No.
intact
No.
intact
X
h
N
L
M O L
-F 0
E L- W
L-
m
+ ' a m
V ) & @
L O C O
U=*+
m
V)
C U - 0
W h h
Skeletal representation (Table 1)
Eighty-six per cent of the bone, representing a minimum of 25 M. musculus
individuals, survived the digestion of T. czlba. Only two elements, the clavicle and t h e
sternebra, are represented by less than SO%, and 90% of the 12 largest elements were
recovered. In contrast, only 21% of the bone representing a minimum of 15 M.
musculus individuals survived the digestion of N. boobook. All but two bone types,
the femora and the crania, are represented by less than 50%, and only 37% of the 12
largest elements were recovered. The common elements t o both T. alba and N.
boobook t h a t have the highest percentage present are the crania, the femora and t h e
mandibles.
The common under-represented elements are the sacrum, clavicle,
sternebra, and t o a lesser extent, the vertebrae.
D a m a g e frequencies (Table 2)
Of the 495 M. musculus bones examined from the T. alba pellets, 47% displayed
breakage. More specifically, none of the 24 crania and only five of the 50 scapula
were recovered intact. The next most damaged element was the pelvis (74%)
followed by the sacrum (69%). Damage frequencies for the long bones varied
between 67% for the humeri and 4% for the radii; the latter being the element least
frequently damaged. Of the 124 M. musculus bones examined from N. boobook
pellets. 89% displaved breakage. Only t'hree individual units, a mandible, humerus
and radius, were recovered intact.
Tables 3 and 4 record in more detail the location of damaged areas on t h e elements
recovered from both sets of pellets. While these only relate the location of damage, a
more detailed description of its extent and manifestation is warranted.
Cranial elements
Damage to the crania from T. alba pellets was concentrated a t the distal end, leaving
up to half of the individual units intact. Disarticulated parietals and occipitals were
usually recovered undamaged. Eighty per cent of nasals had become detached and
20% of crania displayed minor frontal damage. For all 24 u n i t s the zygomatic and
squamosal bones were also disarticulated, and in two cases the area immediately
posterior t o the palatine was severely eroded. In comparison, all but one of t h e 15
crania from the N. boobook pellets were represented by fragments. The frontals,
parietals and occipitals were either not present or reduced t o small, severely eroded
pieces. Of the cranial components that were recovered, the nasals and bullae were
more often the least damaged. The complex consisting of the maxilla, maxillary and
malar process was usually present and displayed relatively minor digestive erosion.
The single unit that was partially articulated resembled those crania recovered from
the T. alba pellets.
Mandibles
For t h e mandibles recovered from both T. alba and N . boobook pellets, damage was
more frequent a t the back end; in some cases affecting both t h e coronoid and
condyloid processes.
At t h e front end, the area immediately posterior t o the
mandibular symphysis was either eroded, exposing the lower incisor or completely
broken away. Damage was more severe on the mandibles recovered from N. boobook
pellets.
Girdle elements
Predictably, the blade was the most frequently damaged area on the scapula. For
those recovered from T. alba pellets the extent of this was variable, ranging from
slight erosion of t h e edges t o the detachment of the entire feature. The broken
portions of the blade were usually recovered. Excluding the recovery of such pieces,
this pattern of damage was repeated for those scapulae recovered from N. boobook
pellets, though generally it was more severe. In both cases the ventral end of the
spine was represented and usually intact.
Damage t o t h e pelves from T. alba pellets was concentrated a t the illiatic crest and
was manifested a s surface etching and breakage along the caudal edge. Damage to
the pubis a n d ischium was also normally situated a t the caudal edge. In a few cases,
however, one or both features were completely broken away. For most of these
pelves both the acetabulum and illiatic spine remained undamaged. Concerning the
pelves from N. boobook pellets, the acetabulum was the site t h a t was least often
damaged. Damage t o the other features was extensive and almost always resulted in
their detachment.
Long bones
For the humeri from the pellets of both species, the proximal end comprising the
head and greater tubercle was the area most often damaged. The distal end of all
units from T. alba pellets remained intact. Breakage t o the shaft of those recovered
from N. boobmk pellets was infrequent, but both proximal and distal ends were
usually damaged. Damage t o the deltoid tuberosity on humeri from both species
pellets was variable, ranging from slight serration of the protruding edge to the
detachment of the entire feature.
Both the ulna and the radius are small delicate bones. Damage t o those from N.
boobook pellets was indiscriminate and resulted in obtuse breaks along their lengths
and extensive surface erosion. In contrast, both bone types from T. alba pellets rarely
displayed damage of either type.
Damage t o t h e femora from T. alba pellets was minor. and usually resulted in the
detachment of the head a t the proximal end and the condyle and flabellas a t the
distal end. For those from N . boobook pellets the distal end was often completely
broken away and the shaft eroded along its length.
T h e tibia and fibula are fused distally and damage to those from T. alba pellets, like
other long bones, was relatively minor. Damage t o the proximal end of the tibia
resulted in the detachment of the head and for all but one unit t h e distal end
remained intact. In contrast, the tibia-fibula bones from N. boobook pellets were
damaged a t both their distal and proximal ends, and the fibula was often detached.
Axial elements
The clavicle and sacrum were the smallest of the bone types examined for damage.
The clavicles usually had their proximal and/or distal ends removed. T h e transverse
processes of the sacra were often detached - the smaller posterior units more often
than the anterior ones for those recovered from 7'. alba pellets.
In summary, the digestion of M. rnusculus bone by T. alba was infrequent. The
largest elements, the cranium, scapula and pelvis, were the most often damaged,
while the mandible and the smaller long bones, the fibula, ulna and radius, were
usually recovered intact. For most elements the location of breakage on individual
units was similar and the detached areas of bone were usually represented. Damage
in the form of surface erosion was minimal. The digestion of M. musculus bone by
N. boobook was frequent and nearly all of the units returned were damaged. Of the
elements considered, the cranium was the best represented, followed by t h e mandible
and the femur. Unlike the damaged units from T . alba pellets, the detached portions
were usually lost to digestion and much of the surface bone was eroded. While the
extent of such darnage for most elements w a s variable, particular areas of bone were
consistently represented, e.g. the articular end of scapulae. These observed patterns
in bone representation form the basis of the predictions of owl-deposited bone.
INTERPRETATIONS
In an attempt t o define general characteristics of owl pellet accumulations, Dodson
and Wexlar (1979) compared the M. musculus skeletal remains from t h e pellets of
three species of owl. T.alba, the only one common with this analysis, digested less
bone and returned the greatest proportion of undamaged elements, including
articulated vertebrae and metapodials (Dodson and Wexlar 1979:277, 282). The
absolute amount of digested M. musculus bone varied between the three owls and
ranged between 20-50%. However, for all three species the scapula and the pelvis
were the most commonly damaged elements, while the mandible and the femur were
the elements most often returned intact (Dodson and Kexlar 1979:277). While this
similarity between owls was not repeated here, Dodson and Wexlar's observations
regarding the location of damage and the areas of bone most likely t o be represented,
are comparable to those presented above (Dodson and Wexlar 1979:278-80).
Importantly, none of the M. musculus crania were returned intact in their study;
those recorded as being complete lacked the back half (Dodson and Wexlar
1979:278). Dodson and Wexlar conclude t h a t the relative frequencies of bone and
observed patterns of breakage are probably characteristic of owls generally (Dodson
and Wexlar 1979:283).
In a similar study Raczynski and Ruprecht (1974) documented the amount of skeletal
digestion which occurred t o small mammals and birds fed t o three species of owl. For
all prey the pelvis was the most commonly digested element (up t o 80%) followed by
t h e skull ( u p t o 35%), while the mandibles of mammals were the element most often
returned in pellets (Raczynski and Ruprecht 1974:28-30). Again t h e amount of
skeletal digestion between owls varied and this, they concluded, was primarily due to
physiological differences. T. alba was the species that digested the least amount of
bone (Raczynski and Ruprecht 1974:30-32).
Prehension, ingestion and digestion
Both Dodson and Wexlar (1979) and Raczynski and Ruprecht (1974) note that the
condition of owl pellet bone is the consequence of the combined effects of three
behavioural factors:
1 . the mode of prehension, i.e. the way in which prey is caught;
2. the mode of consumption or ingestion; and
3. t h e extent of chemical digestion.
During this study neither T. alba nor N . boobook were observed feeding (cf. Dodson
and Wexlar 1979:282-83). However, on the basis of the observations of others (Fleay
1968; Schodde and Mason 1980; Dodson and Wexlar 1979) it can be expected that
t h e major structural damage t o the more robust M. musculus elements such as the
large long bones, occurred during capture and/or consumption. More specifically,
both T. alba and N . boobook seize the head of their victim in their talons and proceed
t o break its neck (Fleay 1968:90; Schodde and Mason 1980:81). Such a mode of
prehension is t h e likely cause of the damage which was concentrated a t the distal end
of the M. musculus crania.
It should be noted t h a t the popular notion that owls consistently swallow their prey
whole (see Mayhew 1977) appears to be false. If small enough, prey will be bolted
head-first. However, prior t o consumption, dismembering associated with crushing
and fur-plucking may also occur (Fleay 1968:90; Schodde and Mason 1980:73, 78:
Dodson and Wexlar 1979:282-83).
All three studies demonstrate t h e ~elect~ivity
of the digestive process; smaller and
more fragile bones are returned with comparatively little damage (Dodson and
Wexlar 1979:282; Raczynski and Ruprecht 1974:30). This would suggest that bone
hardness is not t h e sole determinant of damage susceptibility. While the largest
elements were most often damaged, the shape or relative surface area of bone may
prove t o be important. For this study a t least, it appears that the minor breakage
and erosion such as t h a t which occurred on the illiatic crest of pelves is probably a
result, of chemical digestion.
,An important difference between owls and diurnal raptors (falconiforms) relates to
stomach acidity. T h e gastric juice of owls has a pH of 2.35 which is higher than that
of falconiforms with a pH of 1.66 (Cummings et al. 1976:55; Duke et al. 1975:651).
Consequently hawks and falcons digest bone more thoroughly and return less in their
pellets (Cummings et al. 1976:56; Mayhew 1977:29-31). While diurnal raptors do
inhabit caves in Australia ( Hamilton-Smith 1965:153) their contribution of bone via
their pellets will not be a s important, in terms of quantity. as that deposited via owl
pellets.
In summary, the quantitative results and general observations presented here are
supported by the findings of both Dodson and Wexlar (1979) and Raczynski and
Ruprecht. (1974). The damage t o the M. musculus bone from the pellets of T.alba
and N. boobook as described in the last section, represents the combined effects of a
number of factors.
DISCUSSION
The presence of large quantities of unbroken small mammal bone in cave deposits in
Australia is generally taken t o be indicative of owl predation. Concentrations of
murid and dasyurid bone have been recognised as being a consequence of pellet
accumulation (Wakefield 1963:132; Hall 1975:35). Smaller, more discrete clusters of
bone and associated dentaries deriving from the same individual and representing
partially disintegrated pellets have also been noted (Archer and Baynes 1972:86).
Where either occurs owl occupancy has probably been intense and the amount of
post-depositional disturbance minimal. However, the mixing of owl pellet bone with
bone originating from the activities of other predators, such as marsupial carnivores
or humans, is common and presents problems of interpretation.
Hope (1973) has suggested several characteristics for distinguishing bone derived
from owl pellets. These are:
.
1. the bones are generally unbroken, and whole skulls may be present;
2. the animals represented are small, with the largest about the size of a
bandicoot; and
3. the largest sized animals are represented by juveniles (Hope 1973:ll).
These characteristics were met by a portion of the small mammal fauna from Cloggs
Cave, all of which Hope attributes to owls (Hope 1973:6). Lundelius (1966) offers a
similar set of criteria, but states that skulls will frequently be disarticulated
(Lundelius 1966:175). Both Hope and Lundelius contrast owl pellet bone with bone
derived from the scats of marsupial carnivores which they consider t o be more
fragmented and t o represent larger species (Hope 1973:7; Lundelius 1966:176). T h a t
less fragmented bone associated with small mammal species is attributable t o owls
has also been suggested by others (e.g. Archer and Baynes 1972:86; Dortch and
Merrilees 1971:112).
In accordance with Hope's first criterion the identification of owls as the predator
type responsible for the small mammal fauna has depended, in part, on this fauna
being represented by undamaged bone. Unfortunately, where such bone has occurred,
the descriptions of both its quantity and condition have, at, best. been superficial, e.g.
'Many of the bones of the rodents are unbroken and there are a few whole skulls'
(Bowdler 1979:166). In support of this criterion, much of the M. musculus bone
from the T. alba pellets remained intact and breakage t o many elements is relatively
minor when compared t o bone derived from the scats of other cave-dwelling
predators. i.e. Sarcophilus (see Douglas et al. 1966). It is apparent, however, t h a t
the condition of owl pellet bone is more variable than this criterion implies. The
results presented here and those of other analyses, i.e. Dodson and Wexlar (1979) and
Raczynski and Ruprecht (1974), do suggest that unbroken bone is not necessarily
characteristic of owl prey and that the occurrence of such elements will vary
according tpothe species of owl and probably the size of its prey.
For two main reasons this analysis, as an evaluation of Hope's first criterion, is far
from complete. Firstly, bone from T. novaehollandiae, the largest of the caveroosting owls, was not documented and the occurrence of whole crania and less
broken bone may generally be the result of predation by this particular species.
Indeed, T. novaehollandiae will pull the head off prey that is too bulky t o carry and
ingest it 'more or less intact' (Schodde and Mason 1980:73). Secondly, only one prey
size was fed t o T. alba and N. boobook. Many of the rodents found in cave deposits
a r e larger than M. musculus and the pat'terns of pellet bone representation from prey
t h e size of Rattus for example, remains unknown.
Predicted characteristics of bone deposited by T.dba and N. boobook
T h e results of this analysis indicate that the possible contribution of T. alba in terms
of quantity of bone would be much more significant than that of N. boobook. Despite
this difference, particular bone types were consistently recovered in both species'
pellets and t h e following predictions are based on these similarities. As a partial
alternative t o Hope's first criterion, small mammal bone, i.e. M. musculus in size,
deposited by T. alba or ,N. boobook would show the following:
1 . Crania will be well represented. Damage to partially articulated units will be
concentrated in t h e parietal and occipital regions, but these component,^ may be
present. T h e most frequent cranial portion will be the complex consisting of the
maxilla, maxillary and malar. The bullae. squamosal, zygomatic and nasals will also
be present in smaller numbers.
2. Mandibles will be abundant. Breakage will mostly occur towards the back,
affecting t h e angle and the two processes.
3. Scapulae will most often be represented by the ventral end including the two
processes. If present and articulated the blade will almost always be broken. Of the
large bone types t h e scapula will be the most frequently damaged.
4. Femora will be t h e most abundant and the least damaged of the larger long bones.
If breakage is present it will be located a t the distal end. Damage t o humeri will be
concentrated a t t h e proximal end and along the deltoid tuberosity. T h e tibia will
most often be damaged and for composite types, the fibula will be detached.
5. Ulnae will be the most abundant of the smaller long bones, but t h e radii will be
t h e least often damaged. Damage to both radii and fibulae will be variable but
concentrated a t the distal end.
6. Pelves will occur in numbers equivalent to scapulae but will be less frequently
damaged. They will most often be represented by the acetabula-illiatic spine region.
Damage t o articulated units will occur a t the ischium and pubis, and surface erosion
will occur a t the illiatic crest.
7.
The medium t o small bone types, the clavicles, sacra, sternebra, calcanea and
vertebrae, will be the least represented. The clavicles and sacra will frequently be
damaged.
On the sice and age of owl prey, Hope's second and third criteria
Examples of the native genera that comprise t h e diets of T. alba, N. boobook and T.
novaehollandiae have been noted. While T. alba will take adult Rattus and young
I s d o n , both it and N. boobook would normally concentrate on t h e smaller
terrestrial rodents and marsupials. Both owls are considered t o be incapable of
handling larger, more aggressive mammals such a s large adult Dasyuroides (Schodde
and Mason 1980:81). T. novaehollandiae, however, is a much larger owl and its prey
includes adult Peregrtnus and Trtchosurus (Schodde and Mason 1980:73). Fleay
suggests that the Tasmanian variety is capable of handling Dasyurus viverrtnus and
Thylogale (Fleay 1949:169, 1968:114). While T. novaehoilandiae is not restricted t o
bandicoot-sized prey as is suggested by Hope, larger mammals do comprise a
relatively small proportion of their diet (Schodde and Mason 1980:73).
For all three owls then, the contention that prey will be mostly small and t h a t the
largest individuals will be juvenile in age, is supported by the available quantitative
d a t a on diet. However, this size and age range of prey is certainly not exclusive t o
owls (see Bowdler 1979:165, Table 3.28), and until more specific ranges are defined,
viable alternatives to Hope's second and third crit.eria will not be forthcoming.
Ideally then, unless events of owl pellet deposition are stratigraphically
distinguishable, general characteristics of diet relating t o prey size or age, such as
those suggested by Hope become problematical when used a s proveniencing criteria.
Indeed, explicit attempts to apply such criteria have been relatively unsuccessful.
For example, in Bowdler's analysis of the bone from the Pleistocene unit of Cave Bay
Cave it was noted that '... the sets of criteria for owls on the one hand, and marsupial
carnivores on the other, are both partially met' (Bowdler 1979:166). Recognising the
overlap in the size of prey taken by these predator types, Bowdler rightly concluded
t h a t attribut.ing the small mammal fauna t o owls was arbitrary. This was despite a
higher ratio of small mammal species and the occurrence of undamaged bone in this
unit (Bowdler 1979:166-68).
It is recognised here that concentrations of small mammal bone or large numbers of
such fauna throughout an archaeological cave deposit is best explained with reference
to owl predation. However, identifying owls as probable contributors of bone and
distinguishing this bone from that deposited by other agents, such as humans or
marsupial carnivores, are not necessarily one and the same. With the application of
criteria such as those suggested by Hope they have been treated as such.
CONCLUSION
This analysis has been an attempt to evaluate critically the criteria that have been
used t o identify owl-deposited bone in Australian archaeological cave sites. It has
been demonstrated that two of the three species of owl most likely t o roost in caves
do in fact regurgitate damaged bone. While this damage is relatively minor, i.e.
relative t o the bone derived from the scats of other predators, it is apparent t h a t
~lndarnagedb o ~ i eis not rlccessaril! ctraracteri5t ic of o u 1 prcaj arrd t trt~rc~for~~
st~oultir~ot
t>cl used in isolation t o at tribute srr~alln~arnrrial fii111rat o this predator. As a partial
altcrnatik e t o t hc 'undamaged' criterion. st.\ rbral prt~1ictic)ris rcblat i ~ l g t o boric'
rc.presentat ion h a \ t x been suggested. Duv to t he> 1ir11it at ions of t h ~
ar~aljsis,these
predictions a r c restricted t o Al. rrr11sculu.s sizcd proj of T. ulba and *\'. boobook. A
more complcte ctiaracterisatiori of t h e bone reprewrit irrg the preq of o n Is will onl) be
a( hie\ ed u trilr~:
I . .If. Tr) u.\ruIt~.<hor~ofrorr~t he' pc~lletsof 'l'. ~ / o ( * ( it)ol1(1
f
T / ( ~ I U Pis docu ~ I ( B tI I
i r ~a sir~~ili-tr
v, a! . and t h e rcs111ts corrlparcd u i t h t hosv p r i ~ ~odr ~at)()\
l c:
arid
2. uherr t h c patterns of pellet borre rcprewr~tatiori frorri a rarlgcb of larger
prey. i.e. H c ~ t ut s t o lsc~ocioriand 7 ' r i c h o s u r ~ 1 . ~
for
. at least 7'. cllha ancl 7'.
noz~aehollundiueis knou 11.
I ' n t i l more d a t a bccornes a\ailat)lv. the predictions do wrve as a rt~firrc~rr~t~nt
of the1
assclss~du i t h c o r n p a r a t i ~c data
'undamaged' criterion. Their 11t i l i t j sho~lldalso
on the bone frorri the. p r e of ot llcr prc~dators of srlrall rrlarnrnal faur~a.
ACKNOWLEDGEMENTS
1 ~ o u l dlikc. t o thank t h e Zoologit a1 Hoard of \-icat oria for permission t o corlduct the
s t u d . and 1,isa Qilarst arid her staff at t h e Rojal \lelbourne Zoo for collectirig t t ~ c
pellet S . 1 M oultl also like t o thank Elery Hamilton-Srnith of t h e J'rcqt on lrlst it ute of
l'echnologg for t h e pcrsonal coriini~~r~icatiorl
and ericouragernc.nt. l l a i id IZaher G a p of
the .4ust raliari Rapt or .-Iswciat ior~for suggestirig \ aluable refererit cs. and the Ro! a1
Australasian Ornithological I r~iori for the use of their r~lagr~ific(~rit
librarj. l a r ~ i
indebted t o L)r J'aul Ossa for suggest irig and super\.ising the stud! . a r ~ dR u d ) I. rank
for his c o n t i ~ i u di r ~ t c r e \ t . 7'11arlh4 are also dueh to I3ot) Haird of t h~ 1)cpartment of
E a r t h Sciences. \Ionash Lrii\e.r\itj. Richard E'ullagar and ('arolirli~ Hird for
commenting on tar1if.r drafts. I uould especial1 like t o thanh Dr Jearrrrettt. Hope for
encouraging t h e p11hlicat io11 of t tie a r ~ a lsis
) arid for her decisi\ e conl~lrent5 . Daniel
Zobel gab e his t irncn and ad1 i c c. \\ i t h corriputtr niat t c.rs arid Cat hic \$ ebb i d i t ed and
typed early drafts.
REFERENCES
Hondler. S. 1979 Hunter Ilill. Iluntcr Island.
S a t i o n a l 1 nix ersit y : ('an brrra
l*rip~lt)lishr~d
P h D thesis.
.4ustralian
Calaby, J.11. 1969 Nocturnal birds of prey. I n H.J. Frith (pd.)
A u s t r a l i a n High C o u n t r y , pp.134-41. Reed: Melbourne
Birds i n the
Cook, M.S. 1965 T h e A n a t o m y of t h e Laborutory Mouse. Academic Press: London
Cummings, J.H., G.E. Duke and A.A. Jegers 1976 Corrosion of bone by solutions
simulating raptor gastric juice. Raptor Research 10(2):55-57
Dodson,
P. and D. Wexlar 1979 Taphonomic investigations of owl pellets.
Paleobiology 5(3) :275-84
Dortch, C.E. and D. Merrilees 1971 A salvage excavation in Devil's Lair, Western
Australia. Journal o f t h e Royal Society of W e s t e r n A u s t r a l i a 54(4):103-13
Douglas. A.M., G.W. Kendrick and D. Merrilees 1966 A fossil bone deposit near
Pert h, Western Australia, interpreted a s a carnivore's den after feeding tests
on living Sarcophilus (Marsupialia, Dasyuridae). Journal o f the Royul
Society o f W e s t e r n Australia 49:88-90
Duke. (;.E.. A.,4. Jegers, G . Loff and O . A . Evanson 1975 Gastric digestion in some
e
r y a n d Physiology 55A:619-56
raptors. C o r n p u r a t i ~ f Hiochenzisf
Dwyer, P.D. 1966 Mortality factors of the bentwinged bat.
83(2):31-36
Victorian N u t u r a l i s t
Fleay. D. 1949 T h e Tasmanian masked oul. T h e Etnu 65(2):169-76
Fleay. I). 1968 Nightzr~atchmenof B u ~ ha n d H a i n , .4ustralian O w l s a n d O w l - l i k e
B i r d s . Jacaranda Prcss: Brisbane
Hall, L.S. 1975 A recent bone deposit at Marble Arch, XSM'. I n A.\Z'. G r a h a m
(ed .) Proceedings of the T e n t h B i e n n i a l C o n f e r e n c e of t h e A u s t r a / i a n
Australian Speleological Fedclrat ion:
Speleological Federat ion. pp.35-46.
Sydney
Ha~nilt,on-Smith,E. 1965 Birds in Australian caves. T h e E m u 65(2):1.52-55
]lope. 3.11. 1973 Analysis of bone from Cloggs Cave, Buchan. NE l'ictoria. In J . 3 1 .
Flood. T h e moth hunters - inve9tigations towards a prehistory of the southeastern highlands of -Australia. Appendis X I \ . pp. l - 13. I'npublished P h D
thesis. Australian National I-niversity: Uanlwrra
Lundelius. E.L. 1966 Marsupial carnivore dens in Australiar~ c-a1.e~. S t u d i e s i n
Speleology l ( 4 ) :173-80
May hew. D.F. 1977 A v i a n predators as a r c u ~ ~ ~ uors
l a to f fossil marnr~lal material.
Boreas 6:25-31
McKean, L.J. 1963 Masked owl a t Huchan. Vzctorian Naturalist 79(9):263
Morton, S.R. 1975 The diet of the barn owl T y i o alba in southern Victoria.
E m u 75(1):31-34
The
Morton, S.R., M. Happold, A.K. Lee and R.E. MacMillen 1977 T h e diet of t h e barn
owl, T y t o alba, in south-western Queensland. Australian W i l d l i f e Research
4(1):91-97
Morton, S.R. and A.A. Martin 1979 Feeding ecology of the barn owl T y t o alba, in
arid southern Australia. Australian Wildlife Research 6(2):191-204
Purchase, D. 1972 A report on the banding of barn owls.
Bander 10(4):74-75
The Australian Bird
Raczynski, J. and L. Ruprecht 1973 The effect of digestion on t h e osteological
cornposition of owl pellets. .4cta Ornithologica 14:25-38
Schodde, R. and l..]. Mason 1980 Nocturn.al Birds of Australia.
Edi t,ions: Me1bourne
Lansdowne
1971 The f a u r ~ a . l r i K . V . S . Wright (d.)
Archueolvyy o/ the G u l l u s
Szte, Koonalda C a v e , pp.45-47. Australian Institute of Aboriginal Studies:
Canberra
Thorrle, A.G.
Wakefield, N.A. 1960 Recent mammal bones in t h e Buchan district - 2.
.Naturalist 77(8):227-40
Victorian
Wakefield, N.A. 1963 Mammal remains from the Grampians, Victoria.
.Vat uralist 80: 130-33
Victorian
1964 Mammal sub-fossils from basalt caves in south-western
Wakefield, %.A.
Victoria. Victorian Naturalist 80(9):271-78
Department of Archaeology
La Trobe University
BUNDOORA V I C 3083