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RESEARCH ARTICLE
A systematic review of factors affecting
wildlife survival during rehabilitation and
release
Holly R. CopeID
1
*, Clare McArthurID
2
, Christopher R. DickmanID
2
, Thomas M. Newsome
2
,
Rachael Gray
1
, Catherine A. HerbertID
2
1Sydney School of Veterinary Science, Faculty of Science, University of Sydney, NSW, Australia, 2School
of Life and Environmental Sciences, Faculty of Science, University of Sydney, NSW, Australia
*holly.cope@sydney.edu.au
Abstract
Millions of native animals around the world are rescued and rehabilitated each year by wild-
life rehabilitators. Triage and rehabilitation protocols need to be robust and evidence-based,
with outcomes consistently recorded, to promote animal welfare and better understand pre-
dictors of wildlife survival. We conducted a global systematic review and meta-analysis of
112 articles that reported survival rates of native mammals and birds during rehabilitation
and after release to determine intrinsic and extrinsic factors associated with their survival.
We assessed survival during rehabilitation and in the short- and long-term post-release,
with the hypothesis that survival will vary as a function of species body size, diel activity pat-
tern, trophic level and study location (region of the world). We aimed to determine the direc-
tion of effect of these factors on survival to assist in decision-making during triage and
rehabilitation. Results showed that mammals and birds were equally likely to survive all
stages of rehabilitation, and survival rates varied between locations. Birds in North America
had the poorest survival rates post-release, particularly long-term, as did diurnal and carniv-
orous birds in the short-term post-release. Anthropogenic factors such as motor vehicle col-
lisions and domestic or feral animal attack contributed to morbidity and post-release
mortality in 45% (168 of 369) of instances. The reasons for rescue and associated severity
of diagnosis were commonly reported to affect the likelihood of survival to release, but fac-
tors affecting survival were often species-specific, including bodyweight, age, and charac-
teristics of the release location. Therefore, evidence-based, species-specific, and context-
specific protocols need to be developed to ensure wildlife survival is maximised during reha-
bilitation and post-release. Such protocols are critical for enabling rapid, efficient rescue pro-
grams for wildlife following natural disasters and extreme weather events which are
escalating globally, in part due to climate change.
Introduction
Wildlife rehabilitation is practiced in many countries, resulting in the rescue, care, and release
of millions of animals every year [1]. Wildlife commonly require rehabilitation due to
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OPEN ACCESS
Citation: Cope HR, McArthur C, Dickman CR,
Newsome TM, Gray R, Herbert CA (2022) A
systematic review of factors affecting wildlife
survival during rehabilitation and release. PLoS
ONE 17(3): e0265514. https://doi.org/10.1371/
journal.pone.0265514
Editor: Christopher A. Lepczyk, Auburn University,
UNITED STATES
Received: November 9, 2021
Accepted: March 3, 2022
Published: March 17, 2022
Copyright: ©2022 Cope et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
files.
Funding: H.R.C. was supported by a postdoctoral
fellowship funded by the Morris Animal Foundation
(D21ZO-510) and the Sydney School of Veterinary
Science. The funders had no role in study design,
data collection and analysis, decision to publish, or
preparation of the manuscript.
Competing interests: The authors have declared
that no competing interests exist.
collisions with motor vehicles, abandonment and domestic animal attack (among others),
while many targeted rescues are in response to environmental disasters such as oil spills or
wildfire [2,3]. Wildlife rehabilitation has been defined as “the act of providing temporary care
for injured, sick or orphaned wildlife with the goal of releasing them back into the wild” [4].
Although there is limited evidence of the fate and contribution of released animals to the con-
servation of populations or species [1,5], there are other reasons why rehabilitation can be
valuable, or valued. For example, release of rehabilitated animals may help to supplement and
maintain existing populations [1,3,6–8]. Wildlife care and rehabilitation often garner atten-
tion from the community and media and serve as effective education and fundraising tools [2,
9]. The knowledge and experience gained while rehabilitating commonly encountered species
can also support the care of threatened species [2]. Rehabilitation can also be supported for
ethical, legal and welfare concerns in certain situations, varying by country [10,11]. For these
reasons, wildlife rehabilitation is likely to continue, and assessments of the factors affecting
wildlife survival during rehabilitation and release can help to inform future directions.
To identify factors influencing the success of wildlife rehabilitation, it is first necessary to
define “success”, and this may vary among stakeholders. From a wildlife rehabilitator’s per-
spective, success could constitute recovery from initial injuries and release back into the wild
[12]. Success for the individual animal could entail recovery from injuries and long-term sur-
vival in the wild with successful reproduction [13]. Success at the population level could consti-
tute persistence of populations where rehabilitated animals are released, with released animals
maintaining individual territories and contributing to the reproductive population, without
introducing deleterious genetic alleles or disease, or pushing the population beyond the carry-
ing capacity of the habitat or exacerbating intraspecific competition [6,7]. Such measures of
success at the population level likely mirror those for the success of a conservation reintroduc-
tion, which has been defined as the creation of a self-sustaining population [14]. In this review,
we consider success in terms of individual animal survival during care, and short- and long-
term survival post-release. However, the potential impact of released rehabilitated animals at
the population level remains a knowledge gap for many species.
Communities and native animals rely on volunteer wildlife rehabilitators to rescue, rehabil-
itate and release injured or orphaned wildlife [5,15,16]. However, few studies have used an
experimental approach to assess rehabilitation methods or factors associated with survival to
release. Consequently, rehabilitators rely largely on an evolution of methods through trial and
error, shared knowledge and guidelines developed by wildlife authorities [1] (see examples
[17,18]). For example, habituation to humans can reduce survival in the wild if animals do not
display appropriate predator avoidance behaviours [6,19]. However, few studies have quanti-
fied the effect of different measures employed by rehabilitators to avoid habituation [5]. Simi-
larly, limited numbers of studies have monitored survival outcomes post-release in relation to
the rehabilitation methods used [19]. Given the likelihood of increased frequency and severity
of natural disasters in the future, including wildfires [20,21], combined with increased threats
of urbanisation such as motor vehicle collisions, dog attack and entanglement in netting or
wire [16], it is likely that wildlife rescue, rehabilitation and release will play an increasingly
important role in conservation efforts over time [6,22,23]. As such, it is valuable to assess cur-
rent survival rates and factors associated with the success of rehabilitation of rescued wildlife.
We used a systematic approach to review survival rates of native mammals and birds during
rehabilitation and post-release to determine factors associated with survival. We focused on
mammals and birds as these classes are commonly rescued and rehabilitated, with survival
data subsequently reported in the literature. The effects of a range of intrinsic and extrinsic fac-
tors on survival were evaluated to develop a framework of key considerations for wildlife reha-
bilitation, and to guide future research on best-practice rehabilitation methods. Specifically,
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we hypothesised that survival rates during rehabilitation and post-release will vary as a func-
tion of species traits that could impact susceptibility to anthropogenic and environmental
threats, such as body size, trophic level and diel activity pattern, and survival will vary between
regions of the world. Thus, survival likelihood will be species- and context-specific.
Methods
Systematic review scope
A standard systematic search strategy, as outlined by Pullin and Stewart [24], was used to iden-
tify peer-reviewed and grey literature reporting mammal and bird survival during wildlife
rehabilitation around the world. Search results were recorded using a Preferred Reporting
Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram [25]. Online data-
bases Scopus and Web of Science were searched along with relevant conference proceedings,
reference lists of selected articles (backwards search) and Google Scholar. The literature search
was completed by H. Cope over a three-month period from January to March 2021, and
included 50 journals, three of which were particularly relevant–Animal Welfare,Journal of
Raptor Research, and Journal of Wildlife Rehabilitation. Additionally, 16 relevant books, sym-
posium proceedings, reports and theses were used. We used search terms relating to the loca-
tion of the study, focal taxa, rehabilitation intervention and survival, without date limits (S1
Table). The online systematic review tool, SysRev, (sysrev.com) was used to reduce the
returned articles based on title, abstract and keywords. As thousands of articles were returned,
they were sorted by relevance then searched until there were 50 consecutive non-selected arti-
cles (an arbitrary number, usually representing two pages of search results, past which relevant
articles were unlikely to be found). Full texts were then reviewed against selection criteria as
follows: research was conducted on native mammals or birds that entered care for any reason;
the sample size and a survival measure and timeframe (e.g. number of mortalities, annual sur-
vival rate, minimum known alive) during rehabilitation or post-release were reported; and the
article (or abstract) was available online and in English. Few studies included a control group
or intervention other than rehabilitation, so this was not a requirement for inclusion. Where
studies included a control group, this involved monitoring a sample of wild counterparts,
uninjured animals, or known baseline survival rates for the resident population.
Statistical analyses
Definition of variables
One reviewer created a summary of study characteristics for each article detailing study spe-
cies, sample size, study location, reason for entry into care, percentage of unassisted deaths in
care (i.e. excluding euthanasia), percentage survival to release from care, short- and long-term
survival post-release, factors reported as affecting survival, and causes of mortality. Post-release
survival was categorised as short-term (<six months) or long-term (>six months) to mini-
mise bias between study outcomes. These time frames were selected because some studies
reported survival at multiple time points, and monitoring varied from 14 days to six years. We
considered six months to be a reasonable time for animals to settle into their environment and
forage independently in more than one season. Location was also included in the analyses to
disentangle the potential effects of the suite of species found at a location, varying rehabilita-
tion policies and practices around the world, or other abiotic processes from the biological
characteristics of species.
We used the Encyclopedia of Life (https://eol.org/) to categorise species according to class
(Aves, Mammalia), diel activity pattern (any time, crepuscular, diurnal, nocturnal), average
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adult weight (small <5.5 kg, medium 5.5–100 kg, large >100 kg) and trophic level (herbivores
[primary consumers], omnivores and carnivores/pescatarians [secondary and tertiary con-
sumers], apex carnivores). The adult weight classes were designed to separate species accord-
ing to the Australian critical weight range, i.e. 35 g– 5.5 kg [26], from other species within the
same order and trophic level as we expected smaller species to be more susceptible to preda-
tion and mortality. The largest weight class encompasses mammals that have a greater proba-
bility of being threatened than the medium weight class [27]. There were no avian species in
the largest weight class. Trophic levels were designed to separate dietary niches such as preda-
tors from prey species. These sub-groups were considered sufficient to reduce risk of bias from
individual studies. There were insufficient samples to further stratify studies based on the
methods used.
The reasons for entry into care and causes of post-release mortality were grouped into three
categories—anthropogenic, environmental, and non-specific (those that could not be attrib-
uted)—and reported as frequencies. Factors affecting survival during rehabilitation or after
release were categorised as being related to the event that precipitated entry into care (e.g.
severity and type of injury), intrinsic or individual traits (e.g. body size, behaviour and age),
intervention (e.g. rescue protocols, choice of diet and pre-release training), release environ-
ment (e.g. timing of release, release method and habitat quality), and human-wildlife interface
(e.g. hunting activity and urban expansion), and summarised. These factors were shown statis-
tically or observationally to affect survival in the reviewed articles.
Statistical methods. Statistical analyses were performed in R (version 4.0.5) [28]. A
mixed-effects meta-regression model in the METAFOR package was used to assess the rela-
tionship between survival and characteristics of the study species. Species was included as a
random effect to account for multiple studies on the same species. Effect sizes were weighted
by the sample size due to a lack of reported error measures for most articles (survival was
generally reported as percentage known alive), based on the expectation that variance will
decrease with larger sample sizes. Survival rates and sample sizes were then used to calculate
log-odds of survival. Survival was initially compared between Aves and Mammalia for each
stage of rehabilitation, being the unassisted death rate in care (i.e. deaths not resulting from
euthanasia), survival to the end of rehabilitation (i.e. release to the wild or long-term captiv-
ity), short-term survival post-release, and long-term survival post-release. Each class was
then assessed separately to determine the effect of factors hypothesised to affect survival
including study location (Oceania [and Asia], North America, Europe, Africa and Others
[Middle East, Southern America]) and species’ diel activity pattern, adult weight class and
trophic level at each stage of rehabilitation. Strength of association was first assessed between
all paired combinations of predictors using a Fisher’s exact test, and predictors with a rela-
tionship (p <0.05) were not included together in models. All combinations of predictors
were modelled and Akaike’s Information Criterion (AIC) [29] was used to select the best
model with the lowest AIC value by 2 points. Where no model satisfied this criterion, the
most parsimonious model (least number of predictors) within two points of the lowest AIC
value was selected. Between-study heterogeneity was reported as I
2
[30]. Probabilities of sur-
vival were calculated as a back-transformation of log-odds for single predictor models for
simplicity of interpretation.
Publication bias can exist where small studies with small effect sizes are not published or
there is selective reporting within studies. We tested for bias in METAFOR by creating a fun-
nel plot of effect size versus sampling variance of the effect size for each survival measure [31].
Egger’s test was used for funnel plot asymmetry and trim-and-fill analysis [29] was used to esti-
mate magnitude of publication bias.
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Results
The literature search yielded 5617 publications, of which 187 were initially selected; after
reviewing the full texts, 112 articles satisfied all inclusion criteria (Fig 1). Several articles pre-
sented independent survival results for more than one species or population, and these results
were analysed separately and hereafter referred to as studies, totalling 125. Articles were pub-
lished between 1981 and 2021. Sample sizes ranged from 2–22,344 (mean 1076, median 63).
Eighteen articles included a control group with sample sizes ranging from 3–5726 (mean 684,
median 23). Retrospective studies using wildlife rescue databases contributed to the large
mean sample sizes. Research was mostly conducted in Australia, Europe, North America and
Southern Africa (Table 1). Funnel plot analysis showed an estimated lack of 13 studies with
large effect sizes for unassisted death in care (p = 0.0006) resulting in possible underestimation
in our results, six missing studies with small effect sizes for both rehabilitation survival
(p = 0.0038) and post-release short-term survival (p = 0.0328) resulting in possible overestima-
tion, and no publication bias in long-term post-release survival (p = 0.1397; S2 Table).
Reason for entry into care and causes of mortality
Most reasons for entry into care were anthropogenic in origin, followed by non-specific
causes, with a small proportion attributed to natural environmental causes (Table 2). Most
mortalities in care occurred as a direct result of the initial reason for admission, either by
euthanasia or unassisted death. In eight articles, secondary complications caused death, as
sequelae of the initial reasons for admission or resulting from rescue procedures, treatment, or
captivity. The mean unassisted death rate after entry into care was 17.9% (2.4) and 18.2% (4.0)
Fig 1. PRISMA flow diagram of systematic search strategy and results. Adapted from Page et al. [25].
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for birds and mammals, respectively (overall 17.9% (2.1); presented as mean (SE)). The most
common known causes of post-release mortality were predation (by domestic, feral, native,
and conspecific predators, equalling 24% of all causes), vehicle collision, and illegal shooting
or legal hunting.
Factors associated with survival
There were no differences between classes for unassisted death (p = 0.20) or survival during
(p = 0.08) or after rehabilitation (short-term p = 0.38, long-term p = 0.40); however, not all lev-
els of predictors were present in both classes at all survival stages, so we assessed classes sepa-
rately for effects of study location, diel activity pattern, trophic level, and adult weight class
(referred to as the full model). No factors were significant for either birds or mammals for sur-
vival to the end of rehabilitation (S3 Table). The log-odds of unassisted death during care for
mammals was best explained by trophic level and adult weight class; omnivores had a signifi-
cantly higher (p <0.0001) death rate than carnivores (Table 3;Fig 2) (there was a significant
association between trophic level and diel activity pattern (p = 0.025) and between trophic level
and location (p = 0.046), so these combinations were excluded from models). Short-term post-
release survival of mammals was best explained by two models including trophic level, location
and diel activity with support based on AIC values, although no factors were significant (there
was a significant association between adult weight class and diel activity (p = 0.0001), adult
weight class and location (p <0.001), and diel activity and location (p = 0.046), so these combi-
nations were excluded). For long-term post-release survival of mammals, the full model had the
best fit, although no predictors had a significant effect on survival (S3 Table).
Study location affected the unassisted death rate of birds; North America had the highest
log-odds of death and Oceania had the lowest log-odds of death (Table 3). Mean probabilities
of unassisted death were 10% Oceania, 15% Africa, 17% Others, 20% Europe, and 27% North
America (Fig 3A). For short-term post-release survival, the model with trophic level, diel activ-
ity and location had the best fit for birds, although a large proportion of the variation came
Table 1. Number of published articles from each country or region reporting survival of wildlife during rehabilitation, post-release or during both phases.
Region Rehabilitation Post-release Both Total
Oceania (and Asia)
Australia 7 11 6 24 (21.4)
East Asia 1 0 0 1 (0.9)
New Zealand 1 0 0 1 (0.9)
South Asia 0 1 1 2 (1.8)
North America
Canada 2 0 0 2 (1.8)
North America 10 14 5 29 (25.9)
Several northern hemisphere countries 0 1 0 1 (0.9)
Europe 15 14 3 32 (28.6)
Africa
Southern Africa 6 6 5 17 (15.2)
Others
Middle East 2 0 0 2 (1.8)
South America 0 1 0 1 (0.9)
Grand total 44 48 19 112 (100)
Values presented as total (percentage of grand total).
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from sampling variation (I
2
<50%; Table 3). Studies in Africa had a higher survival probability
than Europe, North America and Oceania (65%, 49%, 55% and 50%, respectively; Fig 3B),
diurnal birds had lower survival probability than nocturnal birds (51% and 64%, respectively,
Fig 3C), and carnivorous birds had lower survival probability than apex predators, herbivorous
and omnivorous birds (45%, 63%, 77%, and 66%, respectively; Fig 3D). Two models including
diel activity, location and trophic level had support based on AIC values for long-term survival
of birds, and study location had a significant effect on survival (p <0.0001; Table 3); North
America had the lowest survival probability (6% North America compared with 31% Europe,
65% Oceania and 72% Africa; Fig 3E).
Factors associated with survival in individual studies
In the reviewed articles, 18 included an experimental design to assess the outcomes of different
methods of rehabilitation (e.g. hand-rearing diet, treatment regime, and soft versus hard
Table 2. Frequency of studies reporting various anthropogenic, environmental and non-specific causes for entry
of wildlife into care, and mortality post-release.
Origin of cause for rehabilitation or mortality Cause of entry into
care
Cause of mortality post-
release
Anthropogenic 117 (48.0) 51 (40.8)
Collision–motor vehicle 13 (5.3) 16 (12.8)
Gunshot or poaching 8 (3.3) 15 (12.0)
Domestic or feral animal attack or predation 11 (4.5) 11 (8.8)
Oil spill 21 (8.6) 0 (0)
Toxicosis or poisoning 12 (4.9) 1 (0.8)
Electrocution/collision with powerlines 8 (3.3) 3 (2.4)
Collision–structure 10 (4.1) 0 (0)
Confiscated 10 (4.1) N/A
Relocated or displaced 4 (1.6) 1 (0.8)
Entanglement 3 (1.2) 1 (0.8)
GPS or VHF collar injury N/A 1 (0.8)
Other (e.g. capture myopathy, trap, tree felling, human
interference)
17 (7.0) 2 (1.6)
Environmental 24 (9.8) 36 (28.8)
Disease 19 (7.8) 6 (4.8)
Predation by native predator or conspecific 1 (0.4) 19 (15.2)
Misadventure (burrow collapse, drowning, ingested wasp,
killed by elephant)
0 (0) 6 (4.8)
Fire, flood or storm 3 (1.2) 2 (1.6)
Natural mortality–age-related N/A 3 (2.4)
Heat stress 1 (0.4) 0 (0)
Non-specific 103 (42.2) 38 (30.4)
Generic trauma or unidentified illness (i.e. Sick, injured,
trauma, exhaustion)
41 (16.8) 7 (5.6)
Orphaned or stranded juvenile 46 (18.9) N/A
Malnutrition 8 (3.3) 5 (4.0)
Unresolved initial ailment N/A 7 (5.6)
Unknown causes 8 (3.3) 19 (15.2)
Studies that did not cite a specific reason 10 11
Values presented as number of studies, not number of individuals, with percentage of the total in brackets.
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release). Fifty-eight studies statistically assessed the effect of various factors on survival, and 38
included observations of factors that authors believed affected survival rates in their study
(Table 4). Most factors were intrinsic to the individual or species (e.g. body size, age, and sex),
or related to the interventions enacted by humans in the rescue, rehabilitation and release pro-
cess (e.g. rescue protocol, habituation to humans, and release location) (Table 4).
Table 3. Summary of mixed-effects meta-regression models with the best fit and significant predictors of survival for bird and mammal classes for each survival
stage.
Unassisted death log-odds
Aves (I
2
= 87.36)
a
Estimate s.e. Z-value Lower Upper P-value
Intercept
b
-1.76 0.13 -13.62 -2.02 -1.51 <0.001
locationEurope 0.35 0.12 2.97 0.12 0.59 0.003
locationNorthAmerica 0.75 0.13 5.96 0.50 1.00 <0.001
locationOceania -0.43 0.22 -1.92 -0.87 0.01 0.055
locationOther 0.14 0.26 0.55 -0.37 0.65 0.582
Mammalia (I
2
= 97.56) Estimate s.e. Z-value Lower Upper P-value
Intercept -2.30 1.14 -2.02 -4.54 -0.07 0.043
trophic_levelHerbivore 0.36 0.33 1.09 -0.28 1.00 0.274
trophic_levelOmnivore 1.12 0.33 3.36 0.47 1.78 0.001
adult_weight_classMedium 0.79 1.12 0.71 -1.40 2.98 0.479
adult_weight_classSmall 0.31 1.11 0.28 -1.86 2.48 0.779
Post-release short-term survival log-odds
Aves (I
2
= 40.30) Estimate s.e. Z-value Lower Upper P-value
Intercept 2.56 0.71 3.63 1.18 3.95 <0.001
trophic_levelCarnivore -1.95 0.59 -3.30 -3.10 -0.79 0.001
trophic_levelHerbivore 0.80 0.94 0.85 -1.04 2.64 0.394
trophic_levelOmnivore -0.31 0.74 -0.42 -1.76 1.13 0.671
diel_activityNocturnal 2.16 0.50 4.29 1.17 3.14 <0.001
locationEurope -2.16 0.52 -4.14 -3.18 -1.14 <0.001
locationNorthAmerica -2.01 0.51 -3.93 -3.01 -1.01 <0.001
locationOceania -0.62 0.80 -0.78 -2.18 0.94 0.438
Post-release long-term survival log-odds
Aves Estimate s.e. Z-value Lower Upper P-value
(I
2
= 98.29) (AIC 198.69) Intercept 1.78 2.09 0.85 -2.32 5.88 0.395
diel_activityDiurnal -0.85 2.02 -0.42 -4.81 3.11 0.674
diel_activityNocturnal -1.26 1.99 -0.63 -5.17 2.64 0.527
locationEurope -1.60 0.87 -1.85 -3.30 0.09 0.064
locationNorthAmerica -3.70 1.03 -3.59 -5.72 -1.68 <0.001
locationOceania -0.17 1.04 -0.16 -2.21 1.87 0.871
(I
2
= 97.77) (AIC 197.87) Intercept 0.92 0.49 1.90 -0.03 1.88 0.058
trophic_levelHerbivore 0.93 0.86 1.07 -0.76 2.61 0.283
trophic_levelOmnivore 1.49 1.90 0.78 -2.23 5.21 0.433
locationEurope -2.01 0.76 -2.62 -3.50 -0.51 0.009
locationNorthAmerica -3.59 0.93 -3.88 -5.41 -1.78 <0.001
locationOceania -0.80 0.87 -0.92 -2.52 0.91 0.357
a
I
2
reports between-study heterogeneity
b
the mixed-effects meta-analysis function treats the first alphabetical factor level as a baseline with an estimate of zero; i.e., locationAfrica, trophic_levelApexPredator,
diel_activityAnytime, adult_weight_classLarge
P-values <0.05 indicate factor levels that are significantly different from zero
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Post-release survival of rehabilitated and control animals
Only 18 studies incorporated a control group, which was usually a wild cohort that did not
require rehabilitation. Most studies showed either reduced survival for rehabilitated animals
compared with control groups, or similar outcomes (Table 5). Oiling in particular appears to
cause a large decrease in survival after rehabilitation, highlighted in the study by De La Cruz
et al. [40] where oiled rehabilitated surf scoters (Melanitta perspicillata) showed survival of
only 14.3% compared with 49.8% for unoiled non-rehabilitated scoters at five months, while
unoiled scoters rehabilitated for other reasons had 77.2% survival.
Discussion
This systematic review supports our hypothesis that wildlife survival during rehabilitation and
post-release is species- and context-specific. Most studies in this review were from Australia,
Europe, North America and southern Africa. Meta-analysis demonstrated effects of species’
diel activity type, trophic level, and location of the study on survival, but not adult weight, sup-
porting some but not all our hypotheses. Study location was a strong predictor of death in care
and survival short- and long-term post-release for birds. There are various potential explana-
tions for the effect of location, including differing triage protocols and therefore frequency of
euthanasia, impacts of different threats in the environment, and varying perceptions towards
the value of wildlife around the world [3,118,119]. The reason for rescue and associated sever-
ity of diagnosis were strong predictors of survival to release, and in some cases, post-release
Fig 2. Distribution of log-odds across factors affecting unassisted death rates for mammalian species. Note that
each point represents the log-odds of survival of one study-species combination, and the size of the point is
proportional to the inverse variance of the log-odds (i.e. larger points have more weight).
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survival. Our results synthesised five clear categories of factor that can impact survival out-
comes for rescued wildlife and that must be addressed in rescue, rehabilitation and release pro-
tocols. These factors relate to the event, individual animal, intervention, release environment,
and the human-wildlife interface. Oil spill events appear to have stimulated global wildlife
rehabilitation research efforts, with 15 articles published from five countries, and generally
result in low rates of survival. Only two articles (both in Australia) assessed the survival of
rehabilitated wildfire-affected animals, and showed that they had low to moderate rates of sur-
vival [22,109]. Overall, the number of studies that included an experimental approach or con-
trol to assess factors affecting survival was low.
Factors affecting survival during and after rehabilitation
Unassisted deaths in care can act as an indicator of ineffective triage criteria and appropriate
treatment and husbandry protocols, as these are animals that die without euthanasia. The rates
of unassisted death varied depending on the study location for birds, and by trophic level for
mammals. This variation could indicate that the decision to euthanise is made sooner in Ocea-
nia compared with North America, or that threats in North America are more likely to result
in unpredictable death in care. The only omnivorous mammals with unassisted death rates
recorded in the meta-analysis were raccoon dogs (Nyctereutes procyonoides) and European
hedgehogs (Erinaceus europaeus), both with relatively high death rates. Hedgehogs that were
admitted due to trauma, parasite infections and vehicle collisions had very low recovery rates,
and road casualties died very quickly in care [56,61]. Raccoon dogs treated in Japan for severe
Fig 3. Distribution of log-odds across factors affecting unassisted death rates and short- and long-term post-release survival for avian species. Note that
each point represents the log-odds of survival of one study-species combination, and the size of the point is proportional to the inverse variance of the log-odds
(i.e. larger points have more weight).
https://doi.org/10.1371/journal.pone.0265514.g003
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Table 4. A summary of factors associated with wildlife survival during rehabilitation and after release, with the direction of effects (higher or lower probability of
survival), and factors categorised into event-related, intrinsic or individual (inter-specific and intra-specific), intervention-related, release environment, and
human-wildlife interface (see S5 Table for full list of species referenced).
Factor Phase affected Higher probability of survival after rescue Lower probability of survival after rescue
Event-related
Reason for admission and
associated diagnosis and
severity
Survival to release
[32–58]
Less severe reason for rescue or diagnosis, e.g.
uninjured orphans
a
More severe reason for rescue or diagnosis, e.g.
fracture
a
Survival post-release
[34]
Less extensive oiling
a
More extensive oiling
a
Size of disaster Survival to release
[33,59]
Major oil spill event i.e. greater search and recovery
effort
a
[59]
Widespread events (e.g. heat stress) can overwhelm
rehabilitator capacity
b
[33]
Season of admission Survival to release
[54]
N/A
c
Coincides with physiologically taxing events, such as
breeding or moulting
a
Intrinsic or individual—inter-specific
Body size Survival to release
[60]
Larger body size
b
N/A
Migratory or not Survival post-release
[60]
Non-migratory (i.e. no strain of migration soon after
release)
b
Migratory (i.e. become oiled far from breeding
localities)
b
Behaviour Survival to release
[61]
Resilient and easily adapts to captivity
b
N/A
Survival post-release
[62]
Easily adapts to post-release environment
b
N/A
Intrinsic or individual—intra-specific
Age Survival to release [6,
33,36,37,44,50,53,
57,59,63–66]
Juveniles may present with less severe injuries such as
orphaning, so have greater survival than adults
a
[6,33,
36,37,44,50,53,57,66]
Juveniles can have lower survival than adults
a
, often
due to characteristics of their age such as moult,
presence of an umbilicus (susceptible to infection) or
differing fitness requirements [59,63–65]
Survival post-release
[67,68]
Juvenile pelicans had better survival than adults
a
[68] Juvenile (hand-reared) possums did not survive as long
as adults
a
[67]
Sex Survival to release
[47,51,69]
Male polecats were more likely to be released than
females
a
[69]
Male sparrowhawks were less likely to be released than
females
a
[51], male raptors were more susceptible to
unassisted mortality than females [47]
Survival post-release
[34]
Male little penguins had higher survival rates than
females
a
[34]
N/A
Bodyweight Survival to release
[37,54,57,59,64,
70–72]
Heavier bodyweight at time of rescue
a
Lower rescue mass and poor rescue condition
a
Survival post-release
[34]
As above
a
As above
a
Individual personality Survival post-release
[73]
More exploratory individuals
a
Less exploratory individuals
a
Brood size Survival to release
[72]
Improved juvenile survival when larger brood is
rescued
a
N/A
Physiological parameters Survival to release
[41,54]
Higher body temperature, higher packed cell volume
and higher total plasma protein
a
[41]
Low total plasma protein, low haematocrit
a
[54]
Activity pattern Survival to release
[44]
Young diurnal raptors were admitted more frequently
and had greater release rates than adults
a
Adult nocturnal raptors were admitted more
frequently than young birds
a
. Diurnal birds were more
often treated for fractures than nocturnal birds
a
Intervention-related
Personnel and facilities
for rescue, transport, care,
and release
Survival to release
[35,36,59,60,74–
78]
Readily available and adequately equipped care
facilities, trained personnel, and refined protocols
b
Birds delivered by the public to the wildlife care centre
(versus an animal collection officer or veterinarian)
bb
;
time delay between event (e.g. oil spill) and rescue or
veterinary treatment
b
Survival post-release
[75,79]
As above
b
N/A
(Continued)
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Table 4. (Continued)
Factor Phase affected Higher probability of survival after rescue Lower probability of survival after rescue
Wildlife care centre Survival to release
[36,80]
Some centres had higher survival
a
, possibly due to
increased levels of experience and appropriate triage
and treatment regimes
Some centres had lower survival
a
, possibly due to lower
levels of experience and ineffective or inappropriate
triage and treatment regimes
Choice of hand-raising
diet
Survival to release
[71,81]
Artificial milk-replacer had greater survival than fish-
formula
a
, and a commercial milk-replacer was better
than another brand
a
N/A
Maintenance of
bodyweight
Survival post-release
[74,82–85]
Sufficient fat reserves or heavier mass on release
ab
Weight loss in migratory birds
b
Treatment regimens Survival to release [6,
35,66,86]
Individuals with a better response to treatment
a
;
disease management and ancillary treatment
a
Treatment based on clinical signs rather than
diagnostic tests
b
; incorrect drug dosages given by
rehabilitators
b
, inappropriate treatments
b
Survival post-release
[66,68,87–89]
Appropriate disease management
b
Inadequate oil removal procedures
b
; failure to
eliminate pathogen before release
b
Habituation to humans Survival to release
[6]
Less human-imprinted animals are more likely to
survive
a
[6]
N/A
Survival post-release
[6,34,67,73,85,90–
93]
Shorter periods of rehabilitation may be better
b
[67],
although duration did not affect little penguin
survival
a
[34]
Loss of wild behaviours such as predator avoidance
and disruption of social development due to human
habituation
ab
, although habituation was not related to
survival in deer
a
[90]
Hunting and wild
behaviour training
Survival to release
[78]
Construction of a pre-release flight tunnel for raptors
b
[78]
N/A
Survival post-release
[91,94–97]
Provision of suitable hunting training
b
Lack of pre-release training to navigate situations likely
to be encountered in the wild
b
; the mother-fawn
relationship is essential, so hand-reared fawns lacked
traits required for survival
b
[97]
Formation of social
groups in captivity
Survival post-release
[93,98,99]
Formation of social groups and surrogate mentor
females provided for juveniles
ab
.
Lack of group cohesiveness prior to release
b
.
Readiness for release Survival post-release
[40,68,79,84,85,
89,100,101]
Yearling age improves survival in bear cubs
a
; adequate
waterproofing and bouyancy for water birds
b
Released with unresolved ailments or long-term effects
from reason for rescue
b
Release environment
Timing of release Survival post-release
[67,76,79,82,100]
Release during the non-breeding season
a
; mild
weather
b
; high prey or food availability
b
Majority of hedgehog mortalities occurred during
spring when they are most active
a
[82]
Release method Survival post-release
[60,62,82,97,98,
101–104]
Release to a wild flock or known congregation area
b
;
release of female macropods in groups with other
female rearing companions
b
; soft release
b
[97,101,
104]
a
; release close to breeding locations
b
Hard released Asiatic black bears had shorter survival
than soft-released bears
a
[104]
Familiarity of habitat Survival post-release
[13,34,67,90,105–
107]
Familiar release habitat may not be necessary for all
species [34,67,105]
b
Unfamiliar release habitat
b
Habitat quality Survival post-release
[67,92,95,107–113]
Unfamiliar habitat may be suitable while there are
sufficient food trees and the carrying capacity has not
been exceeded
b
[67,108]
At or near carrying capacity
b
; reduced canopy
continuity following bushfires
b
; competition and
attacks from conspecifics
b
; the need to immediately
travel long distances
b
; the presence of illegal hunting
activity and proximity to dwellings and roads
b
.
Predators Survival post-release
[8,22,95]
Control or absence of predators
b
Presence of predators
b
Human-wildlife interface
Increasing human
population and habitat
fragmentation
Survival post-release
[65,114]
N/A Stress associated with bushfires and habitat
fragmentation may be contributing to disease in
koalas
b
Hunting activities Survival post-release
[84]
N/A Survival rates of bears reflect their permitted hunting
pressure
b
(Continued)
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Sarcoptes scabiei infections experienced 57.4% and 38.9% unassisted death rates for two groups
given different treatment regimens [86], allowing the researchers to determine the best treat-
ment to reduce future unassisted deaths. The greatest death rate recorded in the review was
61.3% for little penguins (Eudyptula minor) rescued after an oil spill event in Australia [35].
Most mortalities occurred within the first 12 days, and were attributed to the degree of oiling,
the amount of oil ingested, the low body weight of penguins on arrival, and inappropriate
cleaning techniques used by inexperienced and unsupervised volunteers [35]. An oil spill five
years later showed greatly improved survival rates for little penguins, with only 5% unassisted
deaths [34], highlighting the importance of evaluating outcomes and refining protocols over
time [77].
In the reviewed articles, there were several large mammalian species with high short-term
post-release survival rates. In our meta-analysis, large species included Asiatic black bears
(Ursus thibetanus), American black bears (U.americanus) and brown bears (U.arctos) in
Table 4. (Continued)
Factor Phase affected Higher probability of survival after rescue Lower probability of survival after rescue
Urban expansion Survival post-release
[84]
N/A Increasing encounters in recolonised areas results in
more illegal kills
b
a, b
Factors identified by statistical or other inference (denoted by superscript a and b, respectively) that affected survival to release or survival post-release.
c
N/A indicates fields where no relevant data were presented. If survival to release or survival after release do not appear under phase affected for a given factor this
indicates that no studies assessed that phase.
https://doi.org/10.1371/journal.pone.0265514.t004
Table 5. Post-release survival of rehabilitated and control groups of various wildlife species grouped by survival pattern between the two groups.
Species Rehabilitated group survival Control group survival
Rehabilitated group survival less than control group
Common ringtail possums (Pseudocheirus peregrinus)
[106]
101 days 182 days
Little penguins (Eudyptula minor) [34] 59% (Ninth Island), 44% (Low Head) 77% (Ninth Island), 50% (Low Head)
Brown pelicans (Pelecanus occidentalis californicus) [68] 9% at 2 years 53% at 2 years
Common murres (Uria aalge) [79] 45% at 60 days 92% at 60 days
Common murres [12] 39 days 485 days
Cape vultures (Gyps coprotheres) [7] 74.8% annual survival 91.3% annual survival
American coots (Fulica americana) [115] 49% at 4 months 76% at 4 months
Surf scoters (Melanitta perspicillata) [40] 14.3% at 5 months 49.8% at 5 months
Rehabilitated group survival greater than control group
Hedgehogs (Erinaceus europaeus) [83] 73.1% at 8 weeks 63.6% at 8 weeks
Surf scoters [40] 77.2% at 5 months 49.8% at 5 months
Rehabilitated group survival similar to control group
Sea otters (Enhydra lutris) [93] 71% at 1 year 75% at 1 year
Koalas (Phascolarctos cinereus) [22] 58% annual survival 67% annual survival
Carnaby’s cockatoos (Zanda latirostris) [98] 73% annual survival 61% - 69% annual survival
Hedgehogs [82,116] 57% at 38 days 50% at 38 days
Shorebirds [74] 50% at 6 months 52% at 6 months
Western gulls (Larus occidentalis) [76] 100% at 6 months 90% at 6 months
Cape gannets (Morus capensis) [60] 86% (Malgas Island), 88% (Bird Island) annual
survival
88% (Malgas Island), 90% (Bird Island) annual
survival
Peregrine falcons (Falco peregrinus) [117] 14% at 1 year 10–11% at 1 year
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North America and white rhinoceros (Ceratotherium simum) in South Africa. Their high rate
of survival could be associated with the success of the captive rearing process, as most of these
animals entered rehabilitation as orphans [84,108,120], or a reduced risk of predation con-
ferred by their size. In the long-term post-release, birds in North America had particularly low
rates of survival, relating to studies of the peregrine falcon (Falco peregrinus) and brown peli-
can (Pelecanus occidentalis californicus). Anderson et al. [68] determined that rescue and treat-
ment after oiling did not restore pelicans to normal survivability; however, the 14% survival
rate of peregrine falcons was similar to non-rehabilitated peregrines in the same population
[117]. As stated by Morris et al. [13], “rehabilitation cannot confer immortality” (pg. 65), and
released rehabilitated animals are susceptible to the same threats as their wild counterparts
[91], yet not always equally. For example, rehabilitated and wild ringtail possums (Pseudo-
cheirus peregrinus) in Australia faced the same predation pressures, however, translocated
rehabilitated possums were at a disadvantage in unfamiliar territory and initially had lower
survival rates [106].
Few studies have experimentally assessed factors influencing wildlife survival during reha-
bilitation and release [1], yet many of the reviewed articles retrospectively assessed or made
observations of factors that influenced survival in their study. The reason for admission and
the associated severity of diagnosis were both predictors of survival to release in many studies
across a broad range of species, particularly birds [42,44,58]. However, this was not always
the case. For example, the initial cause for rescue had no effect on wombat (Vombatus ursinus)
survival during rehabilitation, where age and response to treatment were predictive of survival
instead [6]. In many avian studies, especially on raptors, the main reasons for admission to
care were trauma and orphaned young, with trauma resulting in lower release rates, while rais-
ing orphaned young was relatively successful [48]. The large proportion of carnivorous/pesca-
tarian birds rescued due to oiling may have contributed to the low short-term post-release
survival of birds revealed by our meta-analysis.
Our review found that intrinsic traits of species or individuals can affect survival outcomes,
yet traits of importance vary with the species and type of injury they sustain. For example, the
large body size and non-migratory nature of Cape gannets (Morus capensis) may have contrib-
uted to higher release rates after oiling than for smaller oiled bird species [60]. Age and body-
weight upon entry to care were often correlated with survival to release, and in some studies,
survival differed by sex. Larger body sizes may contribute to higher release rates in some cases
by conferring a degree of robustness to the animal, or through increased effort contributed to
rehabilitating larger species considered to be charismatic megafauna [121]. Although some
physiological parameters were associated with survival, it can be impossible to define a cut-off
measure to guide triage protocols [70].
The reviewed studies reported many intervention-related aspects of rescue, transport, treat-
ment, and release methods that affect survival pre- and post-release. Habituation to humans
and the associated loss of wild behaviours such as predator avoidance can result in poor sur-
vival [6,73,85,90–92]. Therefore, shorter periods of rehabilitation may be better [67], yet in
this time it is critical to teach hunting, foraging and wild behaviours to support survival [91,
94,95]. Depending on species’ social behaviour, it may be important to form and release social
groups together [112]. The provision of mentor animals could also provide benefits for ani-
mals such as deer, as the mother-fawn relationship has been shown to be essential for survival
[97]. A veterinary examination prior to release is important in assessing readiness in terms of
appropriate age, physical fitness, independence and recovery from disease or injury, and
requirements will vary between species for optimising survival [68,89,101].
Several factors relating to the release environment were found to influence survival of reha-
bilitated wildlife, including the timing of release, release method, quality of the release habitat,
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and presence of predators. Responses varied among species. For example, soft release
improved survival of Asiatic black bears [104], but not kangaroos and tawny owls [102,122].
Habitat familiarity and quality also can be critical for some species’ long-term survival [108].
Thus, an unfamiliar environment contributes to low survival rates for possums, hedgehogs
and deer [13,90,106,107]. For koalas, habitat quality is more important than habitat familiar-
ity [67], possibly due to their specialist feeding habits. A few studies identified effects of the
human-wildlife interface on survival [44]. For example, survival rates of bears reflected hunt-
ing pressures, with increased numbers of encounters in recolonised areas resulting in more
illegal kills by local residents [84].
Limitations of the papers in this review
It is possible that relevant articles were missed in our search, particularly if they were published
in another language, which may be why some regions were not represented in our results. Our
analysis also indicated some publication bias. However, asymmetry in funnel plots does not
always reflect publication bias and can result from other factors such as poor methods leading
to exaggerated effects in smaller studies [31]. Few studies in this review included a control
group, even though comparing survival with a control group is beneficial to assess whether
rehabilitated wildlife is disadvantaged post-release. Lunney et al. [22] found that if they had
examined only rehabilitated burnt koalas, their project would have been determined a failure
due to the low survival rates, yet survival was similar to that of unburnt koalas in the same
area. Another confounding factor was the different post-release monitoring methods, dura-
tions and measures of survival presented by reviewed articles. Some authors presented mini-
mum percentages of animals known to be alive, while others calculated an annual survival rate
or mean days survived, and there were often large numbers of individuals unaccounted for
due to emigration from the monitoring area, failure of tracking collars, or early conclusion of
fieldwork [102]. Several retrospective studies utilising wildlife rescue centre and rehabilitation
databases acknowledged the poor quality and inconsistency of the data recorded [2,3,32,33].
We note that some zoos contribute to rehabilitation research through their wildlife hospitals
and other partnerships. However, these outcomes were not specifically searched for via zoo
webpages, as relevant articles could have been detected in Google Scholar and conference pro-
ceedings searches (outlined in S1 Table).
Lessons from reintroduction biology
There is a wealth of published studies on conservation translocation and reintroduction pro-
grams with varying levels of success [5,14], which could be used to improve release protocols
after rehabilitation. Some wildlife rehabilitation standards and guidelines include a require-
ment that rescued wildlife be returned to the location where they were found, if possible. Yet,
with areas of suitable habitat diminishing [123,124], or when the reason for rehabilitation is
habitat loss (for example, catastrophic bush fires), policies for the translocation of rescued
wildlife may need to be considered where survival will not be negatively affected.
Batson et al. [125] synthesised 30 techniques that have been used in translocation programs
to influence post-release survival, separated into Animal Focused Tactics and Environmental
Focused Tactics. The factors associated with survival presented in Table 4 align with many of
these tactics, and as such could be used as a checklist prior to release of rescued wildlife and as
a guide for future research priorities in rehabilitation programs. Research should be conducted
to support best practice recommendations for each of these tactics, and we recommend that
wildlife rescue organisations ensure that they educate their rehabilitators on these tactics
(where data are available) for species in their region.
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Environmental preconditioning in the form of predator control is an important consider-
ation, particularly for translocation programs, given the large number of failures attributed to
predation [14]. Our results show that introduced and native predators also played a role in
mortalities of released rehabilitated wildlife. There is evidence to support the benefits of pro-
tection from predators (via wildlife training or use of a fence), predator control efforts (e.g.
baiting or shooting), and absence of predators [126–129]. It would be beneficial for environ-
mental managers to engage with wildlife rehabilitation organisations and provide data about
introduced predator and conspecific densities in surrounding habitat, and any intended con-
trol programs, so that suitable release locations can be appropriately identified.
Conservation translocations follow guidelines set by the International Union for Conserva-
tion of Nature [130], which state that post-release monitoring is an essential part of a responsi-
ble conservation translocation with data collected on survival, reproduction and dispersal.
However, post-release monitoring by wildlife rehabilitators is often limited due to lack of
funds, lack of expertise, and onerous requirements for state permission [19]. This is where col-
laboration between university and government researchers and wildlife rehabilitation organi-
sations can provide great benefits. GPS tracking technology would assist post-release
monitoring, and rapid advancements in technology now allow access to devices of smaller size
and greater battery duration at low cost [5].
Recommendations for wildlife rehabilitation and future directions
Adequate resources for rapid rescue responses are key to improving survival rates of wildlife,
particularly after severe or widespread incidents [33,59]. After the Black Summer bushfires in
Australia there were cases where wildlife rescuers could not access fire grounds due to safety
concerns or lack of support [15], highlighting the need for appropriate emergency response
plans and resources [23]. It is also likely that veterinarians will encounter a larger volume and
diversity of wildlife than they are accustomed to during disaster events. As such, it is vital to
develop advice and support services for veterinarians.
Whether or not wildlife rehabilitation contributes to conservation outcomes is debated and
lacks evidence [1], yet it will continue to be practiced around the world and likely play a role in
the persistence of local wildlife populations following increasingly frequent and severe environ-
mental disasters [20,21]. The need to incorporate wildlife rescue into broader disaster response
plans is gaining traction, with some organisations facilitating improvements to disaster pre-
paredness [131] and developing wildlife first aid guidelines [132]. Rescued wildlife is exposed to
the stress of the initial adverse event, in addition to stress occasioned by transport, treatments,
captivity and release [114]. The potential distress experienced by animals needs to be pragmati-
cally weighed with the benefits of survival for the individual, population and species. If animals
are released with a reduced likelihood of survival this presents a potentially serious welfare con-
cern if they are unable to adapt or are more susceptible to threats than wild counterparts. It is
vital that research continues to develop our understanding of basic biology and husbandry
requirements of native wildlife [133], along with factors associated with survival at all stages of
rehabilitation. Our comparison of post-release survival rates between study and control groups
has highlighted the value of including a comparison with a wild cohort in future studies. The
factors highlighted by this review and summarised in Table 4 should be used as a framework to
guide the development and revision of species-specific and evidence-based rescue and treat-
ment protocols globally. With these robust protocols, veterinarians and rescue organisations
can continue to minimise animal suffering and maximise the effectiveness of rehabilitation pro-
grams in an environment affected by climate change and urban expansion. Threat mitigation
must also be prioritised to reduce the need for wildlife rescue in the first place.
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Supporting information
S1 Checklist.
(DOCX)
S1 Table. Summary of the systematic search methods and numbers of articles returned.
(DOCX)
S2 Table. Publication bias funnel plot analysis, eggers test output and trim-and-fill analy-
sis output.
(DOCX)
S3 Table. Summary of mixed-effects meta-regression models with the best fit but no signif-
icant predictors of survival.
(DOCX)
S4 Table. A summary of reviewed articles and the survival measures reported for mammals
and birds during care, and in the short- and long- term post release.
(DOCX)
S5 Table. A summary of factors associated with wildlife survival during rehabilitation and
after release, including relevant species and references.
(DOCX)
S6 Table. Systematic review article data used for meta-analysis.
(XLSX)
Acknowledgments
The authors would like to acknowledge the 2021 Statistical Consulting unit taught by the Uni-
versity of Sydney School of Mathematics and Statistics for their statistical support, in particu-
lar, J. Zhou, S. Chew, and Z.W. Yu who provided the consultation report.
Author Contributions
Conceptualization: Holly R. Cope, Catherine A. Herbert.
Data curation: Holly R. Cope.
Formal analysis: Holly R. Cope, Clare McArthur.
Funding acquisition: Clare McArthur, Christopher R. Dickman, Thomas M. Newsome,
Rachael Gray, Catherine A. Herbert.
Investigation: Holly R. Cope.
Methodology: Holly R. Cope, Clare McArthur, Christopher R. Dickman, Thomas M. News-
ome, Rachael Gray, Catherine A. Herbert.
Project administration: Holly R. Cope, Catherine A. Herbert.
Resources: Catherine A. Herbert.
Software: Holly R. Cope.
Supervision: Catherine A. Herbert.
Validation: Holly R. Cope.
Visualization: Holly R. Cope.
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Writing – original draft: Holly R. Cope.
Writing – review & editing: Clare McArthur, Christopher R. Dickman, Thomas M. News-
ome, Rachael Gray, Catherine A. Herbert.
References
1. Pyke GH, Szabo JK. Conservation and the 4 Rs, which are rescue, rehabilitation, release, and
research. Conserv Biol. 2018; 32(1):50–9. https://doi.org/10.1111/cobi.12937 PMID: 28328146
2. Tribe A, Brown PR. The role of wildlife rescue groups in the care and rehabilitation of Australian fauna.
Hum Dimens Wildl. 2000; 5(2):69–85. https://doi.org/10.1080/10871200009359180
3. Mullineaux E. Veterinary treatment and rehabilitation of indigenous wildlife. J Small Anim Pract. 2014;
55(6):293–300. https://doi.org/10.1111/jsap.12213 PMID: 24725160
4. IWRC. The IWRC: About Us. Eugene, OR: International Wildlife Rehabilitation Council; 2020 [cited
2021 29th March]. Available from: https://theiwrc.org/about-us.
5. Hernandez SM. Postrehabilitation release monitoring of wildlife. In: Hernandez SM, Barron HW, Miller
EA, Aguilar RF, Yabsley MJ, editors. Medical Management of Wildlife Species. Hoboken, NJ 07030,
USA: Wiley-Blackwell; 2019. p. 123–7.
6. Saran KA, Parker G, Parker R, Dickman CR. Rehabilitation as a conservation tool: a case study using
the common wombat. Pac Conserv Biol. 2011; 17(4):310–9. https://doi.org/10.1071/PC110310
7. Monadjem A, Wolter K, Neser W, Kane A. Effect of rehabilitation on survival rates of endangered
Cape vultures. Anim Conserv. 2014; 17(1):52–60. https://doi.org/10.1111/acv.12054
8. Ridgeway P. Rewilding ecosystems through wildlife rehabilitation–a successful trial in Western Syd-
ney. Australian Wildlife Rehabilitation Conference; 2018 Jul 2–4; Sydney, Australia.
9. Mo M, Roache M, Reid T, Oliver D, Broome L, Fawcett A, et al. Corporate support for threatened spe-
cies recovery efforts—three case studies from the 2019–20 Australian bushfire season. Aust Zool.
2020; 41(2):186–93. https://doi.org/10.7882/AZ.2020.031
10. Cooper J, Cooper ME. Ethical and legal implications of treating casualty wild animals. In Pract. 2006;
28(1):2–6. https://doi.org/10.1136/inpract.28.1.2
11. Cooper JE. Precedents, progress and potential. J Raptor Res. 1987; 21(1):21–6.
12. Sharp BE. Post-release survival of oiled, cleaned seabirds in North America. Ibis. 1996; 138(2):222–8.
https://doi.org/10.1111/j.1474-919X.1996.tb04332.x
13. Morris P, Meakin K, Sharafi S. The behaviour and survival of rehabilitated hedgehogs (Erinaceus euro-
paeus). Anim Welf. 1993; 2(1):53–66.
14. Fischer J, Lindenmayer DB. An assessment of the published results of animal relocations. Biol Con-
serv. 2000; 96(1):1–11. https://doi.org/10.1016/S0006-3207(00)00048-3
15. APH. Wildlife impacts of the fires. 2020. In: Lessons to be learned in relation to the Australian bushfire
season 2019–20 [Internet]. Canberra: Finance and Public Administration References Committee,
Australian Parliament House, Commonwealth of Australia. Available from: https://www.aph.gov.au/
Parliamentary_Business/Committees/Senate/Finance_and_Public_Administration/Bushfirerecovery.
16. Kwok ABC, Haering R, Travers SK, Stathis P. Trends in wildlife rehabilitation rescues and animal fate
across a six-year period in New South Wales, Australia. PLoS ONE. 2021; 16(9):e0257209. https://
doi.org/10.1371/journal.pone.0257209 PMID: 34506558
17. OEH. Code of Practice for Injured, Sick and Orphaned Protected Fauna Parramatta, NSW: Office of
Environment and Heritage, 2011 [
18. Miller EA. Minimum standards for wildlife rehabilitation. St. Cloud, MN: National Wildlife Rehabilitators
Association; 2000.
19. Guy AJ, Curnoe D, Banks PB. A survey of current mammal rehabilitation and release practices. Biodi-
vers Conserv. 2013; 22(4):825–37. https://doi.org/10.1007/s10531-013-0452-1
20. Krawchuk MA, Moritz MA, Parisien M-A, Van Dorn J, Hayhoe K. Global pyrogeography: the current
and future distribution of wildfire. PLoS ONE. 2009; 4(4):e5102. https://doi.org/10.1371/journal.pone.
0005102 PMID: 19352494
21. Rogers BM, Balch JK, Goetz SJ, Lehmann CE, Turetsky M. Focus on changing fire regimes: interac-
tions with climate, ecosystems, and society. Environ Res Lett. 2020; 15(3):030201. https://doi.org/10.
1088/1748-9326/ab6d3a
22. Lunney D, Gresser SM, Mahon PS, Matthews A. Post-fire survival and reproduction of rehabilitated
and unburnt koalas. Biol Conserv. 2004; 120(4):567–75. https://doi.org/10.1016/j.biocon.2004.03.029
PLOS ONE
Wildlife survival during rehabilitation and release
PLOS ONE | https://doi.org/10.1371/journal.pone.0265514 March 17, 2022 18 / 24
23. Dickman C, Driscoll D, Garnett S, Keith D, Legge S, Lindenmayer D, et al. After the catastrophe: a
blueprint for a conservation response to large-scale ecological disaster. St Lucia, Australia: Threat-
ened Species Recovery Hub; 2020. Available from: https://www.nespthreatenedspecies.edu.au/
media/0akfale0/after-the-catastrophe-report_v5.pdf.
24. Pullin AS, Stewart GB. Guidelines for Systematic Review in Conservation and Environmental Manage-
ment. Conserv Biol. 2006; 20(6):1647–56. https://doi.org/10.1111/j.1523-1739.2006.00485.x PMID:
17181800
25. Page MJ, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, et al. The PRISMA 2020
statement: an updated guideline for reporting systematic reviews. BMJ. 2021; 372:n71. https://doi.org/
10.1136/bmj.n71 PMID: 33782057
26. Burbidge AA, McKenzie NL. Patterns in the modern decline of Western Australia’s vertebrate fauna:
causes and conservation implications. Biol Conserv. 1989; 50(1–4):143–98. https://doi.org/10.1016/
0006-3207(89)90009-8
27. Ripple WJ, Wolf C, Newsome TM, Hoffmann M, Wirsing AJ, McCauley DJ. Extinction risk is most
acute for the world’s largest and smallest vertebrates. Proc Natl Acad Sci U S A. 2017; 114
(40):10678–83. https://doi.org/10.1073/pnas.1702078114 PMID: 28923917
28. R Core Team. R: A language and environment for statistical computing. Vienna, Austria: R Founda-
tion for Statistical Computing, 2021 [
29. Harrer M, Cuijpers P, Furukawa TA, Ebert DD. Doing Meta-Analysis With R: A Hands-On Guide Boca
Raton, FL and London: Chapman & Hall/CRC Press; 2021 [cited 2021 3 September]. Available from:
https://www.routledge.com/Doing-Meta-Analysis-with-R-A-Hands-On-Guide/Harrer-Cuijpers-
Furukawa-Ebert/p/book/9780367610074.
30. Viechtbauer W. I2 for Multilevel and Multivariate Models: The metafor package: A meta-analysis pack-
age for R; 2021 [cited 2021 3 September]. Available from: http://www.metafor-project.org/doku.php/
tips:i2_multilevel_multivariate.
31. Sterne JAC, Egger M. Funnel plots for detecting bias in meta-analysis: Guidelines on choice of axis. J
Clin Epidemiol. 2001; 54(10):1046–55. https://doi.org/10.1016/s0895-4356(01)00377-8 PMID:
11576817
32. Le Soue
¨f A, Holyoake C, Vitali S, Warren K. Presentation and prognostic indicators for free-living
black cockatoos (Calyptorhynchus spp.) admitted to an Australian Zoo Veterinary Hospital over 10
years. J Wildl Dis. 2015; 51(2):380–8. https://doi.org/10.7589/2014-08-203 PMID: 25647589
33. Mo M, Roache M, Haering R, Kwok A. Using wildlife carer records to identify patterns in flying-fox res-
cues: A case study in New South Wales, Australia. Pac Conserv Biol. 2020; 27(1):61–9. https://doi.
org/10.1071/PC20031
34. Goldsworthy SD, Giese M, Gales RP, Brothers N, Hamill J. Effects of the Iron Baron oil spill on little
penguins (Eudyptula minor). II. Post-release survival of rehabilitated oiled birds. Wildl Res. 2000; 27
(6):573–82. https://doi.org/10.1071/wr99076
35. Jessop R, Du Guesclin P. The effects of an oil spill at Apollo Bay, Victoria, on little penguins Eudyptula
minor in May 1990. Aust Bird Watcher. 2000; 18(5):192–8.
36. Baker PJ, Thompson R, Grogan A. Survival rates of cat-attacked birds admitted to RSPCA wildlife
centres in the UK: Implications for cat owners and wildlife rehabilitators. Anim Welf. 2018; 27(4):305–
18. https://doi.org/10.7120/09627286.27.4.305
37. Kelly A, Halstead C, Hunter D, Leighton K, Grogan A, Harris M. Factors affecting the likelihood of
release of injured and orphaned woodpigeons (Columba palumbus). Anim Welf. 2011; 20(4):523–34.
38. Cousins RA, Battley PF, Gartrell BF. Impact injuries and probability of survival in a large semiurban
endemic pigeon in New Zealand, Hemiphaga novaeseelandiae. J Avian Med Surg. 2012; 26(4):274.
https://doi.org/10.7589/0090-3558-48.3.567 PMID: 22740522
39. Montesdeoca N, Calabuig P, Corbera JA, Cooper JE, Oro
´s J. Causes of morbidity and mortality, and
rehabilitation outcomes of birds in Gran Canaria Island, Spain. Bird Study. 2017; 64(4):523–34.
https://doi.org/10.1080/00063657.2017.1411464
40. De La Cruz SEW, Takekawa JY, Spragens KA, Yee J, Golightly RT, Massey G, et al. Post-release sur-
vival of surf scoters following an oil spill: An experimental approach to evaluating rehabilitation suc-
cess. Mar Pollut Bull. 2013; 67(1–2):100–6. https://doi.org/10.1016/j.marpolbul.2012.11.027 PMID:
23273616
41. Duerr RS, Ziccardi MH, Gregory Massey J. Mortality during treatment: Factors affecting the survival of
oiled, rehabilitated common murres (Uria aalge). J Wildl Dis. 2016; 52(3):495–505. https://doi.org/10.
7589/2015-03-054 PMID: 27187030
PLOS ONE
Wildlife survival during rehabilitation and release
PLOS ONE | https://doi.org/10.1371/journal.pone.0265514 March 17, 2022 19 / 24
42. Naidoo V, Wolter K, Espie I, Kotze A. Vulture rescue and rehabilitation in South Africa: an urban per-
spective. J S Afr Vet Assoc. 2011; 82(1):24–31. https://doi.org/10.4102/jsava.v82i1.64 PMID:
21826834
43. Howard A, Hirschauer M, Monadjem A, Forbes N, Wolter K. Injuries, mortality rates, and release rates
of endangered vultures admitted to a rehabilitation center in South Africa. J Wildl Rehabil. 2020; 40
(3):15–24.
44. Hernandez CL, Oster SC, Newbrey JL. Retrospective study of raptors treated at the Southeastern
Raptor Center in Auburn, Alabama. J Raptor Res. 2018; 52(3):379–88. https://doi.org/10.3356/jrr-17-
16.1
45. Komnenou AT, Georgopoulou I, Savvas I, Dessiris A. A retrospective study of presentation, treatment,
and outcome of free-ranging raptors in Greece (1997–2000). J Zoo Wildl Med. 2005; 36(2):222–8.
https://doi.org/10.1638/04-061.1 PMID: 17323562
46. Maphalala MI, Monadjem A, Bildstein KL, Hoffman B, Downs C. Causes of admission to a raptor reha-
bilitation centre and factors that can be used to predict the likelihood of release. Afr J Ecol. 2021; 00:1–
8. https://doi.org/10.1111/aje.12851
47. Molina-Lo
´pez RA, Casal J, Darwich L. Final disposition and quality auditing of the rehabilitation pro-
cess in wild raptors admitted to a wildlife rehabilitation centre in Catalonia, Spain, during a twelve year
period (1995–2007). PLoS ONE. 2013; 8(4):e60242. https://doi.org/10.1371/journal.pone.0060242
PMID: 23613722
48. Montesdeoca N, Calabuig P, Corbera JA, Rocha J, Oro
´s J. Final outcome of raptors admitted to the
Tafira wildlife rehabilitation center, gran Canaria island, Spain (2003–2013). Anim Biodivers Conserv.
2017; 40(2):211–20. https://doi.org/10.32800/abc.2017.40.0211
49. Rodrı
´guez B, Rodrı
´guez A, Siverio F, Siverio M. Causes of raptor admissions to a wildlife rehabilitation
center in Tenerife (Canary Islands). J Raptor Res. 2010; 44(1):30–9. https://doi.org/10.3356/JRR-09-
40.1
50. So
´s-Koroknai V, Solymosi N, Kriko E, Toth T, Marosan M, Sos E. Examination of morbidity and the
incidence of electrocution in common kestrels (Falco tinnunculus) admitted to the Wildlife Rescue
Centre at the Budapest Zoo and Botanical Garden between 2014 and 2016. Magy Allatorv Lapja.
2020; 142(7):429–38.
51. Kelly A, Bland M. Admissions, diagnoses, and outcomes for Eurasian Sparrowhawks (Accipiter nisus)
brought to a wildlife rehabilitation center in England. J Raptor Res. 2006; 40(3):231–5. https://doi.org/
10.3356/0892-1016(2006)40[231:Adaofe]2.0.Co;2
52. Duke G, Redig P, Jones W. Recoveries and resightings of released rehabilitated raptors. J Raptor
Res. 1981; 15(4):97–107.
53. Mariacher A, Gherardi R, Mastrorilli M, Melini D. Causes of admission and outcomes of long-eared owl
(Asio otus) in wildlife rescue centres in Italy from 2010 to 2014. Avian Biol Res. 2016; 9(4):282–6.
https://doi.org/10.3184/175815516X14739467542487
54. Parsons NJ, Vanstreels RE, Schaefer AM. Prognostic indicators of rehabilitation outcomes for adult
African penguins (Spheniscus demersus). J Wildl Dis. 2018; 54(1):54–65. https://doi.org/10.7589/
2017-06-146 PMID: 29059011
55. Barnett J, Westcott S. Distribution, demographics and survivorship of grey seal pups (Halichoerus gry-
pus) rehabilitated in southwest England. Mammalia. 2001; 65(3):349–61. https://doi.org/10.1515/
mamm.2001.65.3.349
56. Martı
´nez JC, Rosique AI, Royo MS. Causes of admission and final dispositions of hedgehogs admitted
to three wildlife rehabilitation centers in eastern Spain. Hystrix. 2014; 25(2):107–10. https://doi.org/10.
4404/hystrix-25.2–10248
57. Santos ARBMF. Eastern cottontail rabbit (Sylvilagus floridanus) admission causes and corresponding
outcomes at the Wildlife Rehabilitation Center of Minnesota: a retrospective study from 2011 to 2017
[PhD thesis]: Universidade de Lisboa, Faculdade de Medicina Veterina
´ria; 2018.
58. Molony SE, Baker PJ, Garland L, Cuthill IC, Harris S. Factors that can be used to predict release rates
for wildlife casualties. Anim Welf. 2007; 16(3):361–7.
59. Grogan A, Pulque
´rio MJ, Cruz MJ, Oaten P, Thompson R, Grantham M, et al. Factors affecting the
welfare and rehabilitation of oiled murres (Uria aalge) in England and Wales, UK. The International
Wildlife Rehabilitation Council symposium; 2011; Coral Springs, FL.
60. Altwegg R, Crawford RJM, Underhill LG, Williams AJ. Long-term survival of de-oiled Cape gannets
Morus capensis after the Castillo de Bellver oil spill of 1983. Biol Conserv. 2008; 141(7):1924–9.
https://doi.org/10.1016/j.biocon.2008.04.030
61. Garcês A, Soeiro V, Lo
´io S, Sargo R, Sousa L, Silva F, et al. Outcomes, mortality causes, and patho-
logical findings in european hedgehogs (Erinaceus europeus, Linnaeus 1758): A seventeen year
PLOS ONE
Wildlife survival during rehabilitation and release
PLOS ONE | https://doi.org/10.1371/journal.pone.0265514 March 17, 2022 20 / 24
retrospective analysis in the North of Portugal. Animals. 2020; 10(8):1–13. https://doi.org/10.3390/
ani10081305 PMID: 32751458
62. Serangeli M, Cistrone L, Ancillotto L, Tomassini A, Russo D. The post-release fate of hand-reared
orphaned bats: survival and habitat selection. Anim Welf. 2012; 21(1):9. https://doi.org/10.7120/
096272812799129510
63. Camphuysen C, Duiven P, Harris M, Leopold M. Recoveries of guillemots ringed in the Netherlands:
the survival of rehabilitated oiled seabirds. Sula. 1997; 11(3):157–74.
64. Greig DJ, Gulland FMD, Rios CA, Hall AJ. Hematology and serum chemistry in stranded and wild-
caught harbor seals in central California: Reference intervals, predictors of survival, and parameters
affecting blood variables. J Wildl Dis. 2010; 46(4):1172–84. https://doi.org/10.7589/0090-3558-46.4.
1172 PMID: 20966268
65. Charalambous R, Narayan E. A 29-year retrospective analysis of koala rescues in New South Wales,
Australia. PLoS ONE. 2020; 15(10):e0239182. https://doi.org/10.1371/journal.pone.0239182 PMID:
33112860
66. Griffith JE, Higgins DP. Diagnosis, treatment and outcomes for koala chlamydiosis at a rehabilitation
facility (1995–2005). Aust Vet J. 2012; 90(11):457–63. https://doi.org/10.1111/j.1751-0813.2012.
00963.x PMID: 23106328
67. Tribe A. Measuring the success of wildlife rehabilitation. National Wildlife Rehabilitation Conference,
Surfers Paradise; 2005; Gold Coast.
68. Anderson DW, Gress F, Fry DM. Survival and dispersal of oiled brown pelicans after rehabilitation and
release. Mar Pollut Bull. 1996; 32(10):711–8. https://doi.org/10.1016/0025-326X(96)00027-6
69. Kelly A, Scrivens R, Grogan A. Post-release survival of orphaned wild-born polecats Mustela putorius
reared in captivity at a wildlife rehabilitation centre in England. Endanger Spec Res. 2010; 12(2):107–
15. https://doi.org/10.3354/esr00299
70. Haynes E, Erb HN, Nevis J. Statistical analysis of juvenile American robin rehabilitation at Willowbrook
Wildlife Center, Illinois, USA: can admission weight be used to predict rehabilitation outcome? J Wildl
Rehabil. 2013; 33(1):19–23.
71. MacRae A, Haulena M, Fraser D. The effect of diet and feeding level on survival and weight gain of
hand-raised harbor seal pups (Phoca vitulina). Zoo Biol. 2011; 30(5):532–41. https://doi.org/10.1002/
zoo.20356 PMID: 21971911
72. Drake A. Mallard duckling care and survival at a wildlife rehabilitation center [PhD thesis]: University of
British Columbia; 2007.
73. Herbert C, Gillies C, Mella V, Webster K, Keong J, Jennings A, et al. Brushtail Possums in Care: Fac-
tors influencing post-release survival and the potential impacts of stress on release outcomes. Austra-
lian Wildlife Rehabilitation Conference; 2018; Sydney, Australia.
74. Rogers DI, Battley PF, Sparrow J, Koolhaas A, Hassell CJ. Treatment of capture myopathy in shore-
birds: a successful trial in northwestern Australia. J Field Ornithol. 2004; 75(2):157–64. https://doi.org/
10.1648/0273-8570-75.2.157
75. Weston MA, Dann P, Jessop R, Fallaw J, Dakin R, Ball D. Can oiled shorebirds and their nests and
eggs be successfully rehabilitated? A case study involving the threatened hooded plover Thinornis
rubricollis in south-eastern Australia. Waterbirds. 2008; 31(1):127–32. https://doi.org/10.1675/1524-
4695(2008)31[127:COSATN]2.0.CO;2
76. Golightly RT, Newman SH, Craig EN, Carter HR, Mazet JAK. Survival and behavior of westerngulls
following exposure to oil and rehabilitation. Wildl Soc Bull. 2002; 30(2):539–46.
77. Parsons N, Underhill L. Oiled and injured African penguins Spheniscus demersus and other seabirds
admitted for rehabilitation in the Western Cape, South Africa, 2001 and 2002. Afr J Mar Sci. 2005; 27
(1):289–96. https://doi.org/10.2989/18142320509504087
78. Thompson LJ, Hoffman B, Brown M. Causes of admissions to a raptor rehabilitation centre in Kwa-
Zulu-Natal, South Africa. Afr Zool. 2013; 48(2):359–66. https://doi.org/10.1080/15627020.2013.
11407603
79. Newman SH, Golightly RT, Craig EN, Carter HR, Kreuder C. The effects of petroleum exposure and
rehabilitation on post-release survival, behavior, and blood health indices: A common murre (Uria
aalge) case study following the Stuyvesant petroleum spill. Final Report. UC Davis, CA: 2004 [1–46].
80. Burton E, Tribe A. The rescue and rehabilitation of koalas (Phascolarctos cinereus) in southeast
Queensland. Animals. 2016; 6(9):56. https://doi.org/10.3390/ani6090056 PMID: 27649249
81. Paul G, Friend DG. Comparison of outcomes using two milk replacer formulas based on commercially
available products in two species of infant cottontail rabbits. J Wildl Rehabil. 2017; 37(1):13–9.
PLOS ONE
Wildlife survival during rehabilitation and release
PLOS ONE | https://doi.org/10.1371/journal.pone.0265514 March 17, 2022 21 / 24
82. Yarnell RW, Surgey J, Grogan A, Thompson R, Davies K, Kimbrough C, et al. Should rehabilitated
hedgehogs be released in winter? A comparison of survival, nest use and weight change in wild and
rescued animals. Eur J Wildl Res. 2019; 65(1):6. https://doi.org/10.1007/s10344-018-1244-4
83. Molony SE, Dowding CV, Baker PJ, Cuthill IC, Harris S. The effect of translocation and temporary cap-
tivity on wildlife rehabilitation success: An experimental study using European hedgehogs (Erinaceus
europaeus). Biol Conserv. 2006; 130(4):530–7. https://doi.org/10.1016/j.biocon.2006.01.015
84. Beecham JJ, De Gabriel Hernando M, Karamanlidis AA, Beausoleil RA, Burguess K, Jeong D-H, et al.
Management implications for releasing orphaned, captive-reared bears back to the wild. J Wildl Man-
age. 2015; 79(8):1327–36. https://doi.org/10.1002/jwmg.941
85. Hashem BJ. Evaluating the success of an orphaned American black bear (Ursus americanus) rehabili-
tation program in Virginia. J Wildl Rehabil. 2019; 39(2):7–12.
86. Kido N, Omiya T, Kamegaya C, Wada Y, Takahashi M, Yamamoto Y. Effective treatment for improving
the survival rate of raccoon dogs infected with Sarcoptes scabiei. J Vet Med Sci. 2014; 76(8):1169–72.
https://doi.org/10.1292/jvms.14-0045 PMID: 24813465
87. Goldingay RL, Dobner B. Home range areas of koalas in an urban area of north-east New South
Wales. Aust Mammal. 2014; 36(1):74–80. https://doi.org/10.1071/am12049
88. Underhill LG, Bartlett PA, Baumann L, Crawford RJ, Dyer BM, Gildenhuys A, et al. Mortality and sur-
vival of African penguins Spheniscus demersus involved in the Apollo Sea oil spill: an evaluation of
rehabilitation efforts. Ibis. 1999; 141(1):29–37. https://doi.org/10.1111/j.1474-919X.1999.tb04260.x
89. Wernham C, Peach WJ, Browne SJ. Survival rates of rehabilitated guillemots. BTO Research. Thet-
ford, Norfolk: British Trust for Ornithology, 1997 [40 p]. Report No.: 186.
90. Beringer J, Mabry P, Meyer T, Wallendorf M, Eddleman WR. Post-release survival of rehabilitated
white-tailed deer fawns in Missouri. Wildl Soc Bull. 2004; 32(3):732–8. https://doi.org/10.2193/0091-
7648(2004)032[0732:PSORWD]2.0.CO;2
91. Houser A, Gusset M, Bragg CJ, Boast LK, Somers MJ. Pre-release hunting training and post-release
monitoring are key components in the rehabilitation of orphaned large felids. Afr J Wildl Res. 2011; 41
(1):11–20. https://doi.org/10.3957/056.041.0111
92. Miazga K, Joubert J, Sinclair M, Cywińska A. Releasing three orphaned white rhinoceroses (Cera-
totherium simum) to the game reserve in South Africa. Rehabilitation, translocation and post-release
observations. Animals. 2020; 10(12):1–15. https://doi.org/10.3390/ani10122224 PMID: 33260863
93. Nicholson TE, Mayer KA, Staedler MM, Johnson AB. Effects of rearing methods on survival of
released free-ranging juvenile southern sea otters. Biol Conserv. 2007; 138(3):313–20. https://doi.org/
10.1016/j.biocon.2007.04.026
94. Houser A. Spoor density, movement and rehabilitation of cheetahs in Botswana [Masters thesis]: Uni-
versity of Pretoria; 2009.
95. Suarez C, Gamboa E, Claver P, Nassar-Montoya F. Survival and adaptation of a released group of
confiscated capuchin monkeys. Anim Welf. 2001; 10(2):191–203.
96. Kelly A, Goodwin S, Grogan A, Mathews F. Further evidence for post-release survival of hand-reared,
orphaned bats based on radio-tracking and ring-return data. Anim Welf. 2012; 21(1):27. https://doi.
org/10.7120/096272812799129420
97. Williams SC, Gregonis MA. Survival and movement of rehabilitated white-tailed deer fawns in Con-
necticut. Wildl Soc Bull. 2015; 39(3):664–9. https://doi.org/10.1002/wsb.562
98. Groom CJ, Warren K, Mawson PR. Survival and reintegration of rehabilitated Carnaby’s cockatoos
Zanda latirostris into wild flocks. Bird Conserv Int. 2018; 28(1):86. https://doi.org/10.1017/
S0959270916000642
99. Wimberger K, Downs C, Perin M. Postrelease success of two rehabilitated vervet monkey (Chloroce-
bus aethiops) troops in KwaZulu-Natal, South Africa. Folia Primatol. 2010; 81:96–108. https://doi.org/
10.1159/000314636 PMID: 20668387
100. Blair CD, Muller LI, Clark JD, Stiver WH. Survival and conflict behavior of American black bears after
rehabilitation. J Wildl Manage. 2020; 84(1):75–84. https://doi.org/10.1002/jwmg.21783
101. Meyer FC. Survival and distribution of Temminck’s pangolin (Smutsia temminckii) retrieved from the
illegal wildlife trade in South Africa [Masters thesis]: University of Venda; 2020.
102. Campbell L, Croft D. Comparison of hard and soft release of hand reared eastern grey kangaroos. Vet-
erinary conservation biology, wildlife health and management in Australasia, proceedings of interna-
tional joint conference; 2001; Sydney: Taronga Zoo.
103. Barman R, Choudhury B, Ashraf NVK, Menon V. Rehabilitation of greater one-horned rhinoceros
calves in Manas National Park, a World Heritage Site in India. J Wildl Rehabil. 2019; 39(1):17–26.
PLOS ONE
Wildlife survival during rehabilitation and release
PLOS ONE | https://doi.org/10.1371/journal.pone.0265514 March 17, 2022 22 / 24
104. Ashraf N, Dadda T, Boro P, Akhtar N. Walking the Bears—Rehabilitation of Asiatic black bears in Aru-
nachal Pradesh. New Delhi: Wildlife Trust of India; 2008. 1–125 p.
105. Morris PA. Released, rehabilitated hedgehogs: A follow-up study in Jersey. Anim Welf. 1997; 6
(4):317–27.
106. Augee ML, Smith B, Rose S. Survival of wild and hand-reared ringtail possums (Pseudocheirus pere-
grinus) in bushland near Sydney. Wildl Res. 1996; 23(1):99–108. https://doi.org/10.1071/WR9960099
107. Neyens J, Hirst S. Survival of released rehabilitated northern brush tailed possums (Trichosurus arn-
hemensis). Australian Wildlife Rehabilitation Conference; 2014; Hobart.
108. Smith WE, Pekins PJ, Timmins AA, Kilham B. Short-term fate of rehabilitated orphan black bears
released in New Hampshire. HUM-WILDL INTERACT. 2016; 10(2):14.
109. Russell B, Smith B, Augee M. Changes to a population of common ringtail possums (Pseudocheirus
peregrinus) after bushfire. Wildl Res. 2003; 30(4):389–96. https://doi.org/10.1071/WR01047
110. Hamilton LL, Zwank PJ, Olsen GH. Movements and survival of released rehabilitated hawks. Raptor
Res. 1988; 22(1):22–6.
111. Guy AJ, Stone OML, Curnoe D. Assessment of the release of rehabilitated vervet monkeys into the
Ntendeka Wilderness Area, KwaZulu-Natal, South Africa: a case study. Primates. 2012; 53(2):171–9.
https://doi.org/10.1007/s10329-011-0292-0 PMID: 22258755
112. Guy AJ. Release of rehabilitated Chlorocebus aethiops to Isishlengeni Game Farm in KwaZulu-Natal,
South Africa. J Nat Conserv. 2013; 21(4):214–6. https://doi.org/10.1016/j.jnc.2013.01.002
113. Martell M, Redig P, Nibe J, Buhl G, Frenzel D. Survival and movements of released rehabilitated bald
eagles. Biol Conserv. 1992; 62(3):231. https://doi.org/10.1016/0006-3207(92)91069-5
114. Narayan E, Vanderneut T. Physiological stress in rescued wild koalas are influenced by habitat demo-
graphics, environmental stressors, and clinical intervention. Front Endocrinol. 2019; 10:18. https://doi.
org/10.3389/fendo.2019.00018 PMID: 30761085
115. Anderson DW, Newman SH, Kelly PR, Herzog SK, Lewis KP. An experimental soft-release of oil-spill
rehabilitated American coots (Fulica americana): I. Lingering effects on survival, condition and behav-
ior. Environ Pollut. 2000; 107(3):285–94. https://doi.org/10.1016/s0269-7491(99)00180-3 PMID:
15092974
116. Rasmussen SL, Kalliokoski O, Dabelsteen T, Abelson K. An exploratory investigation of glucocorti-
coids, personality and survival rates in wild and rehabilitated hedgehogs (Erinaceus europaeus) in
Denmark. BMC Ecol Evol. 2021; 21(1):96. https://doi.org/10.1186/s12862-021-01816-7 PMID:
34022803
117. Sweeney SJ, Redig PT, Tordoff HB. Morbidity, survival and productivity of rehabilitatedPeregrine Fal-
cons in the upper midwestern U.S. J Raptor Res. 1997; 31(4):347–52.
118. Chardonnet P, des Clers B, Fischer J, Gerhold R, Jori F, Lamarque F. The value of wildlife. Revue
scientifique et technique-Office international des e
´pizooties. 2002; 21(1):15–52. https://doi.org/10.
20506/rst.21.1.1323 PMID: 11974626
119. Barnes E. To what extent are veterinary practices prepared to treat wildlife patients? A cross-sectional
study of perceptions of responsibility and capability of treating wildlife in UK veterinary practices. The
Plymouth Student Scientist. 2017; 10:1–21.
120. Clark JE, Pelton MR, Wear BJ, Ratajczak DR. Survival of orphaned black bears released in the Smoky
Mountains. Ursus. 2002; 13:269–73.
121. Lunney D. Charismatic megafauna. In: Craig RK, Pardy B, Nagle JC, Schmitz O, Smith W, editors.
The Encyclopedia of Sustainability: Vol 5 Ecosystem Management and Sustainability. Great Barring-
ton, MA: Berkshire Publishing, USA; 2012. p. 63–6.
122. Griffiths R, Murn C, Clubb R. Survivorship of rehabilitated juvenile tawny owls (Strix aluco) released
without support food, a radio tracking study. Avian Biol Res. 2010; 3(1):1–6. https://doi.org/10.3184/
175815510X12628917082461
123. Heagney EC, Falster DS, KovačM. Land clearing in south-eastern Australia: Drivers, policy effects
and implications for the future. Land Use Policy. 2021; 102:105243. https://doi.org/10.1016/j.
landusepol.2020.105243
124. Boer MM, de Dios VR, Bradstock RA. Unprecedented burn area of Australian mega forest fires. Nat
Clim Chang. 2020; 10(3):171–2. https://doi.org/10.1038/s41558-020-0716-1
125. Batson WG, Gordon IJ, Fletcher DB, Manning AD. Translocation tactics: a framework to support the
IUCN Guidelines for wildlife translocations and improve the quality of applied methods. J Appl Ecol.
2015; 52(6):1598–607. https://doi.org/10.1111/1365-2664.12498
PLOS ONE
Wildlife survival during rehabilitation and release
PLOS ONE | https://doi.org/10.1371/journal.pone.0265514 March 17, 2022 23 / 24
126. Rendall AR, Coetsee AL, Sutherland DR. Predicting suitable release sites for assisted colonisations: A
case study of eastern barred bandicoots. Endanger Spec Res. 2018; 36:137–48. https://doi.org/10.
3354/esr00893
127. Robinson NM, MacGregor CI, Hradsky BA, Dexter N, Lindenmayer DB. Bandicoots return to Boo-
deree: Initial survival, dispersal, home range and habitat preferences of reintroduced southern brown
bandicoots (eastern sub species; Isoodon obesulus obesulus). Wildl Res. 2018; 45(2):132–42. https://
doi.org/10.1071/WR17040
128. Ross AK, Letnic M, Blumstein DT, Moseby KE. Reversing the effects of evolutionary prey naivete
´
through controlled predator exposure. J Appl Ecol. 2019; 56(7):1761–9. https://doi.org/10.1111/1365-
2664.13406
129. Moseby KE, Cameron A, Crisp HA. Can predator avoidance training improve reintroduction outcomes
for the greater bilby in arid Australia? Anim Behav. 2012; 83(4):1011–21. https://doi.org/10.1016/j.
anbehav.2012.01.023
130. IUCN/SSC. Guidelines for reintroductions and other conservation translocations. Gland, Switzerland:
IUCN Species Survival Commission; 2013.
131. LaFontaine P. Beyond Rescue: Animals in Disaster. IFAW US Disaster Response Report. Washing-
ton, DC: International Fund for Animal Welfare; 2020. Available from: https://d1jyxxz9imt9yb.
cloudfront.net/resource/821/attachment/original/IFAW_ANIMALS_IN_DISASTER_REPORT_FINAL.
pdf.
132. DPIE. Helping wildlife in emergencies. Parramatta, NSW: Environment, Energy and Science, Depart-
ment of Planning, Industry and Environment 2020. Available from: https://www.environment.nsw.gov.
au/-/media/OEH/Corporate-Site/Documents/Animals-and-plants/Native-animals/helping-wildlife-in-
emergencies-200030.pdf.
133. Legge S, Robinson N, Lindenmayer D, Scheele B, Southwell D, Wintle B. Monitoring threatened spe-
cies and ecological communities. Clayton South, VIC, Australia: Csiro Publishing; 2018.
PLOS ONE
Wildlife survival during rehabilitation and release
PLOS ONE | https://doi.org/10.1371/journal.pone.0265514 March 17, 2022 24 / 24
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