| "There
is a growing body of evidence that clearly indicates survival rates are
increasing for rehabilitated animals after release." (D210.6.w6)
Data from
post-release studies varies widely in methodology and in interpretation.
Some studies have taken a "worst case" approach and assumed that
all released individuals not positively identified as alive and well after
release, or found dead at a distance in time indicating prolonged survival
after release, have died. Conversely other studies have taken a "best
case" approach and assumed that all individuals, not either found dead
or returned to rehabilitation within a short time of release, have
survived. Obviously the interpretation of the same return data will vary
considerably depending on which approach is used and it is probable that
the true picture is somewhere in between.
- Each spill is different, involving different oil, different species,
vastly different numbers of oiled casualties to be cleaned and
rehabilitated, and different facilities, supplies and response
capabilities. It is dangerous to extrapolate findings from previous spills
to the likely effectiveness of future responses without considering all
these factors as well as the ongoing improvements in response techniques
and protocols. (J57.12.w1,
P14.7.w16)
- There are large variations between species in success rates for
cleaning and rehabilitation. (D60.7.w7,
D214.2.w2)
- Variation in responses between species makes extrapolation between
species on post-release survival impossible. (P14.7.w16)
The following variables may all affect the survival rate (during
rehabilitation and post-release) of oiled
birds:
- The location of the spill; (P14.7.w16)
- The type of oil; (B197.15.w15,
D9, J4.181.w3,
J29.8.w1, J59.30.w1,
P14.7.w16)
- Efficiency of response (J59.30.w1):
- Whether a search and collection programme is undertaken, and if so,
who by, and whether it is carried out effectively; (P14.7.w16)
- The time oiled animals are in the field before being collected and
their condition when brought in for rehabilitation; (D9,
J4.181.w3, J312.16.w1)
- The time span over which oiled wildlife casualties are retrieved; (D9,
J29.8.w1)
- The type of weather oiled birds are exposed to; (B197.15.w15,
P14.7.w16)
- Condition before oiling; (P14.7.w16)
- Whether or not the birds are stabilised after capture; (P14.7.w16)
- Whether birds are stable before being transported; (P14.7.w16)
- Transport being timely; (P14.7.w16)
- Availability of an appropriate facility; (B197.15.w15,
B334.w1, D9,
J4.181.w3, J29.8.w1,
P14.7.w16)
- Availability of trained, experienced personnel and whether trained personnel
oversee all aspects of the response; (B197.15.w15,
B334.w1, D9,
J4.181.w3, J29.8.w1,
P14.7.w16)
- If no facility was available, the length of time it takes for one to
be found or constructed; (P14.7.w16)
- Whether the facility has adequate water, and in particular
sufficient hot water for washing oiled birds; (P14.7.w16)
- Presence or absence of adequate ventilation in the rehabilitation
facility; (P14.7.w16)
- Species involved; (B334.w1,
J29.8.w1, J59.30.w1,
P14.7.w16)
- Numbers of oiled wildlife casualties; (D9,
J29.8.w1,
P14.7.w16)
- What product is used for oil removal; (P14.7.w16)
- Whether blood parameters are checked before washing was allowed; (P14.7.w16)
- Whether blood parameters are checked before birds were released. (P14.7.w16)
STUDIES OF BIRDS:
- A 1996 analysis of bird ringing recoveries in North America
concluded that most oiled, cleaned and released seabirds survived only
a few days to weeks after release with median days survived of four to
11 days. It also concluded that there had been no improvement in
post-release survival when comparing "recent" (birds cleaned
after 1990) with those cleaned in previous years. For guillemots (Uria aalge - Common murre),
73 of 78 recoveries were within 60 days of release, with only four
more than five months after release and only two of those more than a
year after release (longest time between release and ring return was
919 days). Low long-term ring recovery rates were considered probably
due to low survival. (J58.138.w1)
- This study has been criticised, particularly for generalisations
in its conclusions. It combined data from 13 species, involved
birds oiled in various spills and used just 127 band returns to
conclude that cleaning and releasing oiled birds was ineffective.
(P14.7.w16)
- A study of Pelecanus occidentalis californicus - Californian
brown pelicans (Pelecanus occidentalis - Brown pelican)
found that, compared with control birds, oiled and rehabilitated birds
survived a shorter time, showed reduced movements, and did not join
breeding colonies within two seasons after release. This was despite
released rehabilitated birds having blood chemistry values within the
normal range, normal behaviour and normal body mass at release, and
despite 12 of 23 of the rehabilitated birds showing typical courtship
and pairing behaviour in the one to two weeks before release.
Rehabilitated birds showed high mortality during a stressful time: the
moult followed by winter. There was some evidence that rehabilitated
juveniles survived better than did rehabilitated adults. Transmitters
were attached to the birds using neoprene straps, and weighed about 3%
of bird body weight. [1996] (J313.32.w1)
- A study of Uria aalge - Common murre
(guillemots) in the UK concluded, based on ringing returns, that
survival rates of oiled, rehabilitated guillemots was very low. The
median survival time of oiled rehabilitated guillemots ringed since
1985 and recovered was seven days with a median distance moved prior to
recovery of only 8 km. Survival rates were calculated as averaging 17%
per 30 days in the first 60 days post release and 86% after that to
the end of the first year post release, to give an annual survival of
0.6%: a survival rate of 0.7 to 1.3% of natural survival rates for the
species. It was noted that there is some evidence that small numbers
of oiled rehabilitated guillemots do survive and return to breeding
colonies, and even rear young successfully. [1997](B370.3.w3)
- It has been noted that ring returns may give excessive
prominence to short-term losses if the areas close to the release
point are heavily monitored [this gives an increased chance that
birds surviving only a short time will be recovered, compared to
those which survive for longer and are likely to die in areas less
well monitored (thus not be returned)]. [1997](D214.2.w2)
- There may be a bias in analysis when comparing rehabilitated
guillemots released mainly in January to March (i.e. in winter) with unoiled birds
ringed at colonies during the summer months. [1997](D214.2.w2)
- Analysis by South Devon Seabird Trust
of ring return data for guillemots (Uria aalge - Common murre)
which had been cleaned and rehabilitated by the Trust, found (based on
data to March 2003), that for guillemots ringed and released during
1993-1995, the mean time to ring recovery was 394 days and the mean
distance travelled (i.e. distance from the Trust that the ringed bird
was recovered) was 531 km. The data included 13 birds recovered after
less than 35 days, of which 11 were found dead and two were found
re-oiled (one having travelled 126 km by the time it was recaptured),
with a further 15 birds recovered at 54 to 1585 days, of which six
were re-oiled at 54 to 1,321 days, one was seen alive on Skomer, one
was shot in France, one died in a sea trap in France and six were
found dead after 105 to 1,408 days, including two found dead as part
of a large wreck of seabirds in the North Sea. It was considered that
those at liberty for more than 35 days before ringing recovery could
definitely be considered to have been successfully rehabilitated,
while some of those found at less than 35 days may have been
successfully rehabilitated, based on distances travelled and/or time
to ringing recovery. [2001](D184)
- For about 3,000 guillemots (Uria aalge - Common murre)
released after cleaning and
rehabilitation at the West Hatch RSPCA centre, while 70% of ring
returns occurred within two weeks, returns have also occurred after
much longer periods, including several years. [1997](D214.2.w2)
- Of 824 ringed guillemots (Uria aalge - Common murre)
released by the South West Oiled Seabird
Group, while 40 of the 62 returns occurred within two weeks of release, others occurred after much longer periods with ten at more than
two years, one at more than three years, one at five years and two at
more than nine years. [1997](D214.2.w2)
- A radiotelemetry study of rehabilitated Uria aalge - Common murre
following the Stuyvesant spill in northern California in 1999
used 8.5 g radiotransmitters, mounted using the subcutaneous anchor
technique. A total of 31 rehabilitated murres had been found oiled, cleaned,
rehabilitated, assessed as healthy, radio-marked and released
within 17 to 21 days of capture (26 days for one bird), while 25
control birds were captured, radio-marked and released within 24
hours. The mean time for which oiled birds could be tracked was 61
days, maximum 142 days, compared with 80 and 145 days respectively for
control birds. During the study period ten oiled and two control birds
were known to have died. It was noted that these findings suggested
better survival rate and survival duration than had been claimed in
some previous studies. [2001](P60.1.w2)
It was also noted that findings of blood samples taken before release
suggested inflammation and secondary infections subsequent to
petroleum oil exposure/captive care probably contributed to some of
the deaths. Both mean tracking duration and survival (68%) were much
higher than some previous studies on this species had suggested. It
was acknowledged that oiled and rehabilitated individuals were four
times less likely to survive than were control birds. Eighty percent
of mortality in the oiled rehabilitated individuals occurred at 15 to
40 days post release and those which survived for forty days then
appeared to show survival comparable to controls. [2003] (P14.7.w15)
- A study compared 37 oiled, rehabilitated Fulica americana -
American coots (Fulica - Coots (Genus))
with 38 control
coots. All the birds were banded, fitted with numbered coloured neck
collars, fitted with radio-transmitters (with mortality switches) and
wing-clipped on one wing, then released into two marsh areas (20
rehabilitated and twenty control birds into an area of 0.56 ha land
plus 0.46 ha water, the remainder into an area of 1.12 ha land plus
0.46 ha water), and supplementary food provided: i.e. the birds were
soft-released. Birds were able to disperse from the enclosures when
moulting replaced the clipped wing feathers with new complete
feathers. Overall survival was significantly lower in the
rehabilitated coots than in the control birds (49% versus 76%).
Rehabilitated coots were noted to spend more time preening, to sleep
less during the day, and to show feeding and drinking behaviours more
frequently than controls (p <0.05). The rehabilitated birds initially lost
weight in comparison to the controls but then recovered over one to
two months. They showed significantly greater feather wear, completed
their moult sooner, and dispersed from the study area sooner. It was
noted that those rehabilitated coots which did not survive had failed to
regain or maintain body condition. [2000](J316.107.w1,
P59.1.w18)
- A study compared health and blood parameters of oiled, rehabilitated Fulica americana -
American coots (Fulica - Coots (Genus)) with
control coots in a soft-release programme in which the coots were
wing-clipped and released into large, fenced enclosures and blood
sampled at 56, 81, 108 and 140 days. The greatest differences in blood
parameters was noted in the 56-day samples. Oiled coots at 56 days had
higher WBC count, albumin:globulin ration, and calcium concentration
than control birds, and lower MCH,
MCHC, creatine, total protein and
globulin concentrations and alkaline phosphatase, alanine
aminotransferase, and creatine kinase activities. Also at 56 days,
oiled rehabilitated coots which subsequently died had significantly
higher WBC count, PCV, total protein and globulin concentration, and
lower albumin:globulin ratio, MCH, MCHC, glucose and sodium than
control birds which survived. Oiled rehabilitated coots which
subsequently died were found to have high chlorine (> MEQ/L)
or cholesterol (> 449 mg/dL) concentrations at 56 days.
Oiled rehabilitated coots which died had shown higher globulin and
total protein levels than those which survived. From day 81 to day
140, the haematology and clinical biochemistry of oiled rehabilitated
coots was not different from that of the control coots.
Pathologically, oiled rehabilitated coots which died were emaciated
(six of 11), with enlarged spleen (6/11) enlarged thyroids (6/11)
enteritis (4/11), hepatitis (3/11) bile stasis (3/11),
haemosiderin deposition in the liver (4/11), spleen (1/11) and kidneys
(1/11), pododermatitis (3/11) and respiratory lesions including
aspergillosis (3/11), granulomatous pneumonia (2/11) haemorrhage
(2/11) and presence of parasitic granuloma (1/11). It was considered
that inflammation, infection and iron utilisation or metabolism
problems may have contributed to the deaths of those oiled
rehabilitated coots which failed to survive. [2000](J316.107.w2)
- A radiotelemetry study of Western gulls Larus
occidentalis (Larus (Genus))
in California compared survival of oiled rehabilitated birds (oiled
during a crude oil spill ("Torch/Platform Irene Pipeline"
oil spill) with control non-oiled birds and with birds which had not been
oiled, but had undergone the same rehabilitation procedures as oiled
individuals. The cleaning and general rehabilitation of the gulls
followed strict protocols carried out by professional personnel within
the Oiled
Wildlife Care Network. The study tracked birds for up
to 235 days after release and found no difference in survival between the
three groups (one death only, in a control bird), nor were there any
statistical differences (P>0.05) in the size of the geographical
areas used by the birds. Behaviour of individuals in the three groups
(oiled rehabilitated, rehabilitated and control birds) were similar,
as far as could be determined within the limitations of the study.
Although transmitters were no longer working during the breeding
season, data gathered while the batteries lasted indicated that the
oiled rehabilitated gulls visited breeding colony areas "in a
manner similar to control gulls" during both the winter and
pre-breeding seasons. [20001 - 2003](J59.30.w1,
P14.7.w18,
P60.1.w1)
- The same Melanitta nigra - Black
scoters
have been rehabilitated following oiling after successive spills in
the same area (Waddensee) several years apart, indicating survival of
the released birds following the first spill. [1997](P14.5.w8)
- Eudyptula minor - Little penguins (Spheniscidae - Penguins (Family))
in Tasmania which had been
cleaned and rehabilitated, were released 360 km or 540 km from their
site of origin, because their habitat of origin was still oiled.
Radiotracking confirmed that 65% of these birds returned to their site
of origin within four months (this is a minimum estimate of the return
rate, since transmitters had a battery life of only six weeks). [1998](J17.86.w1)
- For Eudyptula minor - Little penguins (Spheniscidae - Penguins (Family))
oiled following the Iron Baron spill, northern Tasmania, Australia,
minimum estimates of post-release survival, based on regular trapping,
was 59% for penguins from North Island and 44% for penguins from Low
Head; at both sites survival was significantly lower than for
non-oiled penguins. Records showed that post-release survival could be
predicted to the greatest extent by the extent of oiling at the time
of capture, and the mass and body condition of oiled birds at the time
of capture (which were affected by the extent of oiling); mass and
condition at the time of release, and the sex of the birds, also
affected survival, while the duration of time in rehabilitation, and
whether or not the birds were translocated a distance (200 to 410 km)
from their capture site for release did not affect survival. [2000](J47.27.w1)
- A study over two breeding seasons after an oil spill, found that for Eudyptula minor - Little penguins
(Spheniscidae - Penguins (Family))
in Tasmania, in the first breeding season oiled-rehabilitated females
had a significantly lower success rate for fledging and egg success:
22% lower probability of oiled-rehabilitated females successfully
fledging any chicks than for control nests or those with an
oiled-rehabilitated male. In the second breeding season there was no
significant difference in breeding success between oiled-rehabilitated
and control birds. Chicks also had lower pre-fledging mass in both
seasons if either parent was oiled-rehabilitated, which may reduce
their survival rates. [1997](P14.5.w12)
- Following oiling and rehabilitation of Jackass penguins (Spheniscus demersus - African Penguin)
on St Croix Island, South Africa in July 1979, 87% of released
rehabilitated penguins had been confirmed returned to the island
by February 1980. The penguins appeared normal, moulted as usual,
returned to former nests and mates and six were confirmed to be
breeding. [1980] (J313.11.w1)
- Following the Apollo Sea oil spill near Dassen Island, off
the coast of South Africa in 1994, in which 10,000 Spheniscus demersus - African Penguin
were oiled, 4,076 of the 5,213 released penguins were flipper-banded.
Of these, 2,652 had been positively resighted at breeding colonies
within two years of release and by August 1996 the number re-sighted
was still rising. Only a few penguins were recovered dead, including
37 within one year of release and a further 12 recoveries in the next
12 months; none provided evidence of death immediately following
release. [1999](J58.141.w1)
- Following the Apollo Sea oil spill near Dassen Island, off
the coast of South Africa in 1994, in which 10,000 Spheniscus demersus - African Penguin
were oiled, 2,962 penguins (nearly 73%) had been re-sighted back at
breeding colonies. The number found dead has always remained below the
expected reporting rate for non-oiled, non-rehabilitated birds and
many birds are known to have survived, two, three, four, or five years
after release. It was noted that, due to the problems in detecting and
reading flipper bands, the numbers re-sighted should be considered
minima of the total of survivors: after five years more penguins were
still being detected for the first time after release. For individuals
oiled in the Dyer Island spill, August 1995, about 40% had been
re-sighted by two years post-release. For individuals oiled in the
Cape Town Harbour spill, May 1998, by 16 months, 50% had been
re-sighted (compared to 45% of the Apollo sea birds seen within one
year of release). It was noted that a greater percentage of birds
which were in adult plumage at the time of oiling were re-sighted than
those which were in juvenile plumage when oiled. Analysis of elapsed
time between banding and death for the oiled rehabilitated penguins
indicated no significant differences in survival: oiled rehabilitated
penguins survived as well as those which had never been oiled.
Comparison of survival rates from live re-sightings using a program
(MARK) which uses Likelihood Ratio Techniques to estimate survival
between specified periods also found non-oiled and oiled rehabilitated
birds to have similar survival rates. Data looking at oldest survivors
also shows that oiled rehabilitated penguins are as likely to survive
into their twenties as are those which have never been oiled. [2003](B334.w2)
- Data from Jackass penguins (Spheniscus demersus - African Penguin)
oiled in the Apollo Sea spill have shown that more than 60% of
rehabilitated penguins re-sighted in the breeding colonies have
attempted to breed, although a small proportion appear not to have
attempted to breed. Possible reasons for non-breeding of some birds include effects of ingested oil
on reproductive physiology, disruption of pair bonds and disruption of
annual breeding cycles. Data on breeding success indicate that, for
the first two years after oiling, when conditions (particularly
feeding conditions) for breeding were good, oiled rehabilitated birds
had similar breeding success to control birds, but that when
conditions have been less favourable, or food in short supply, they
were not as successful at raising chicks and growth rate depression
was greater in chicks from rehabilitated birds during such periods
than in chicks from control birds; there were no detected differences
in chick rearing after the first two years. Other findings included
disruption of the moult cycle in oiled rehabilitated birds during the
first two years, after which synchronisation with non-oiled birds
improved, and a slight disruption of the breeding cycle, with most
oiled birds not attempting breeding until the second year after oiling.
[2003](B334.w3)
- Data from Jackass penguins (Spheniscus demersus - African Penguin)
oiled in the Treasure spill in 2000, compared with those which
were caught unoiled and temporarily relocated, showed that, for data
to 17 April 2002, breeding of those subjected to precautionary capture
was significantly less affected than that of oiled rehabilitated
birds. This was probably due to less disruption to pair bonds and to
breeding and moult cycles as well as the absence of toxic
physiological effects of oil (there was also a probable small sampling
bias since relocated birds were collected from a relatively small area
and were probably more likely to be re-sighted). [2003](B334.w3)
- In general, in is known that mute swans survive well following
oiling and cleaning. [1998](B381.8.w8)
- Mute swans (Cygnus olor - Mute swan)
treated conservatively (supportive care only, not washed) following
oiling with diesel during a river spill, showed significantly higher
mortality than unoiled control birds during the first five months
after release, with at least 33 of the 42 released birds (65%) still
alive at that time. Thereafter, there was no difference in mortality
(based on five years of monitoring). Only one oiled swan bred in the
year following oiling but in subsequent years the swans bred normally
and their productivity was normal. Swans had been released after 30 to
101 days (mean 63 days) in care and 42 of the original 51 birds were
released (the other nine died in care). [1994](J321.94B.w1)
- Following the Santa Clara River oil spill in 1991, in which 166 live
birds were admitted for rehabilitation, and 123 birds were released,
six bands were returned following shooting of the birds by hunters at
10 months to 3.9 years post-release. The birds concerned included two
adult male Anas platyrhynchos
- Mallard, two adult male and one adult female Anas americana - American wigeon
(Mareca americana) and one adult male Anas strepera - Gadwall.
Birds were recovered at 104.6 to 1,014.4 km distance from the release
site. It was noted that the band return data did not provide
information about variables such as whether or not the birds had bred successfully, although it was possible to determine that all the
individuals had migrated successfully at least once after being
released. An aggressive, rapid search and collection response and
immediately available appropriate facilities for initial stabilisation
and treatment, including washing, were considered likely to have
contributed to successful rehabilitation. [1996](P62.14.w1)
- Note: For most species, there is no data on rehabilitation
rates. [1998](B381.8.w8)
STUDIES OF MAMMALS:
- A study on the post-release survival of North American river otters (Lontra canadensis
- Canadian otter)
used in a study on the effects of oil, found that the
otters had lower survival rates than wild otters. Otters which were
found dead from starvation, or that disappeared, relatively soon after
release (21-106 days for the dead otters, 13 and 55 days for those
that disappeared) had had relatively low haemoglobin levels
pre-release. This may have played a role in the non-survival of these
animals, since reduced haemoglobin levels can cause significant
energetic costs and reduce capture of prey. The reduced survival rate
of the experimental otters may have been related to poor food
availability: the otters were released at the end of winter when
schooling fishes were expected to enter the release area, but
migration of fish into this area was delayed, which may have increased
the length of time during which the otters had to cope with food
shortages. [2002](J40.66.w3)
- A study comparing the health status, diving behaviours, activity
patterns, movements and survival of rehabilitated (all causes) harbor
seal (Phoca vitulina - Common seal)
(Phoca vitulina richardsi) pups with free-ranging pups,
using head-mounted radio transmitters and in some pups dorsally
mounted time-depth recorders, found that overall survival and
behaviours were similar. One oiled pup was included in the study, and
one tarred pup. Blood values at the time of release, behaviours
post-release, and post-release survival, for the oiled and tarred pups
were all similar to those of both
wild (never rehabilitated) pups and those rehabilitated for reasons
other than oiling. [2000](P14.5.w15,
P60.1.w34)
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