Protecting wild bird nests against predators: A systematic review and meta‐analysis of non‐lethal methods

Abstract

Implementing effective, affordable and ethical conservation management will be crucial for minimising future biodiversity losses. Such management requires reliable foundational evidence to help managers make informed choices about how to address the needs of their target species. Unfortunately, such evidence is still lacking for many species and management scenarios.
One major global challenge is improving the reproductive success of threatened species in the context of predation. We conducted a systematic review and meta‐analysis of in situ experiments that used non‐lethal methods to protect bird nests against predators, with the aims of summarising global trends in nest protection efforts, comparing the effectiveness of different protection measures and informing future research and management. We considered peer‐reviewed studies in English.
We detected a large geographic and taxonomic bias in the evidence base with 58% of articles conducted in North America and 76% on ground‐nesting birds. Less than 3% of articles involved taxa listed as Endangered or Critically Endangered and 51% of study units lasted just a single breeding season.
Nests protected with exclosures, fences and guards were more likely to be successful than their unprotected controls. Interventions involving deterrents, conditioned taste aversion, chemical camouflage and diversionary feeding did not have a significant positive effect on nest success, but the interventions in these categories were less common and more diverse in nature.
Synthesis and applications. To increase their conservation value, future non‐lethal nest protection experiments should whenever possible clearly state overall aims, take place over multiple seasons, use a comparable control and test non‐lethal protection methods independently of lethal predator control. Greater focus is required on under‐studied taxa such as cup‐nesting songbirds and birds in South America, Africa and Asia, and novel protection techniques such as deterrents and chemical camouflage. Practitioners should consider the evidence we synthesise here when deciding whether non‐lethal nest protection approaches are optimal for their study system, to increase conservation success and reduce ethical and financial costs.

Full text

J Appl Ecol. 2024;61:1187–1198.
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1187wileyonlinelibrary.com/journal/jpe
Received: 21 July 2023
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Accepted: 16 February 2024
DOI : 10.1111/136 5-2664.14619
REVIEW
Protecting wild bird nests against predators: A systematic
review and meta- analysis of non- lethal methods
Daniel Gautschi1 | Antica Čulina2 | Robert Heinsohn1 | Dejan Stojanovic1 |
Ross Crates1
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium,
provided the original work is properly cited.
© 2024 The Authors. Journal of Applied Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society.
1Fenner School of Environment and
Society, Australian National University,
Canberra, Australian Capital Territory,
Australia
2Ruder Boskovic Institute, Zagreb, Croatia
Correspondence
Daniel Gautschi
Email: daniel.gautschi@anu.edu.au
Funding information
Fenner School of Environment and
Society, Australian National University
Handling Editor: Fernanda Michalski
Abstract
1. Implementing effective, affordable and ethical conservation management will be
crucial for minimising future biodiversity losses. Such management requires reli-
able foundational evidence to help managers make informed choices about how
to address the needs of their target species. Unfortunately, such evidence is still
lacking for many species and management scenarios.
2. One major global challenge is improving the reproductive success of threatened
species in the context of predation. We conducted a systematic review and meta-
analysis of in situ experiments that used non- lethal methods to protect bird nests
against predators, with the aims of summarising global trends in nest protection
efforts, comparing the effectiveness of different protection measures and in-
forming future research and management. We considered peer- reviewed studies
in English.
3. We detected a large geographic and taxonomic bias in the evidence base with 58%
of articles conducted in North America and 76% on ground- nesting birds. Less
than 3% of articles involved taxa listed as Endangered or Critically Endangered
and 51% of study units lasted just a single breeding season.
4. Nests protected with exclosures, fences and guards were more likely to be suc-
cessful than their unprotected controls. Interventions involving deterrents, con-
ditioned taste aversion, chemical camouflage and diversionary feeding did not
have a significant positive effect on nest success, but the interventions in these
categories were less common and more diverse in nature.
5. Synthesis and applications. To increase their conservation value, future non- lethal
nest protection experiments should whenever possible clearly state overall aims,
take place over multiple seasons, use a comparable control and test non- lethal
protection methods independently of lethal predator control. Greater focus is
required on under- studied taxa such as cup- nesting songbirds and birds in South
America, Africa and Asia, and novel protection techniques such as deterrents and
chemical camouflage. Practitioners should consider the evidence we synthesise
here when deciding whether non- lethal nest protection approaches are optimal

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1 | INTRODUCTION
The breeding period is a time of particular vulnerability for many
organisms and low rates of breeding success can threaten the per-
sistence of populations. For many species, predation is a prom-
inent cause of breeding failure (Ibáñez- Álamo et al., 2015; Kats
& Ferrer, 2003). While predation is a natural ecosystem process,
anthropogenic habitat changes and exotic species introductions
can drastically alter the composition of predator communities
(Ritchie & Johnson, 2009), putting pressure on vulnerable prey
populations (Doherty et al., 2016). For threatened species fac-
ing elevated predation risk, devising effective ways to reduce
predation rates will be crucial for minimising future extinctions
(Doherty et al., 2016). In the face of persistent global biodiver-
sity loss (Ceballos et al., 2017), implementation of effective,
evidence- based conservation has become a priority (Sutherland
et al., 2004). Implementing conservation actions based on robust
evidence offers high confidence that desired outcomes can be
achieved and ensures effective utilisation of limited conservation
funds (Cook et al., 2017). Evidence- based conservation practices
can also facilitate the ethical refinement of management actions
(Doherty & Ritchie, 2017 ).
For birds—among the most well- studied animals—eggs, chicks
and breeding adults are often susceptible to predation (Ibáñez-
Álamo et al., 2015). The nesting period is therefore a key focus for
managers around the world seeking to implement evidence- based
conservation to boost avian breeding success. Managers may at-
tempt to achieve this via the provision of artificial nest sites (e.g.
Mänd et al., 2005) and good quality habitat/resources required for
nesting (e.g. Narango et al., 2017), exclusion of livestock or people
from nesting areas (e.g. Berger- Geiger et al., 20 19) or through pred-
ator control or exclusion (Smith et al., 2010, 2011). The impact of
nest predator s can be reduced using both lethal and non- lethal tech-
niques. Lethal control involves the trapping, shooting, poisoning or
otherwise killing of target predators to reduce their abundance or
remove them from breeding areas. This can be an effective strategy
in reducing nest predation rates (Smith et al., 2010 ) but can also be
ethically and politically contentious and may result in unintended
impacts on non- target species (Doherty & Ritchie, 2017). In such
instances, non- lethal nest protection measures may be more ethical
and, depending on the approach used, less labour- intensive (Doherty
& Ritchie, 2017). Protecting bird nests from predators using non-
lethal methods often involves the use of physical barriers such as
fences, guards and cages to discourage or prevent predators from
entering a nesting site (Smith et al., 2011). However, an increasing
number of studies are exploring alternative nest protection meth-
ods that manipulate the behaviour of nest predators, such as de-
terrents (e.g. Liu & Liang, 2021), chemical camouflage (e.g. Norbury
et al., 2021) and conditioned taste aversion (e.g. Tobajas et al., 2020).
We conducted a systematic review and meta- analysis of peer-
reviewed, experimental studies of non- lethal nest protection for
wild birds, with two major aims:
1. To provide a global overview of research on non- lethal wild
bird nest protection in order to detect knowledge gaps and
provide guidelines for future research.
2. To examine the efficacy of non- lethal nest protection methods as
a means of increasing wild bird nesting success and test whether
system- specific factors such as nest position and predator taxon
have any detectable influence on their effectiveness.
2 | MATERIALS AND METHODS
2.1 | Criteria for the inclusion or exclusion of
studies
We established strict inclusion and exclusion criteria in order to
identify relevant studies for our meta- analysis. We included only
peer- reviewed studies available in English that were conducted
in situ. Studies were only included if they tested the effectiveness
of non- lethal nest protection, aimed specifically at protecting bird
nests from wild predators and provided nest success data in terms of
daily nest survival rate (DSR) or apparent nest success (i.e. failed or
succeeded). We excluded articles if they involved any form of lethal
predator control, protected nests from threats other than predation,
did not measure nest fate as a binomial outcome or did not contain
a suitable control. We considered a suitable control to be a control
group that closely replicated the conditions of the treatment group
without major confounding factors. We did not consider changes
in nest productivity for this analysis, as nest success was the more
commonly reported measure in the literature.
2.2 | Systematic review
We used two search platforms for our literature search: Web of
Science (WoS) and Scopus. We used the software Covidence (Veritas
for their study system, to increase conservation success and reduce ethical and
financial costs.
KEYWORDS
avian conservation, breeding success, hatching success, nest predation, nest survival, predator
exclusion, wildlife conservation

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Health Innovation, 2023) to streamline the review process. For WoS
we searched for ‘Topic’ within ‘All Databases’ (WoS Core Collection,
Current Contents Connect, KCI- Korean Jour nal Database, MEDLINE and
SciELO Citation Index) and for Scopus we searched ‘Title, Abstract,
Keywords’. We searched for literature on both platforms on the 10th
of October 2023, using a search string designed to capture all rel-
evant literature (Appendix S1).
2.3 | Article screening
Excluding duplicates, our search identified 1297 unique articles,
which passed two- stage screening (Figure S1). All articles under-
went double title/abstract screening by DG and RC. During ab-
stract screening, we reached agreement on inclusion or omission
of 93% of articles. We assessed the remaining articles (n = 86)
further until an agreement was made whether to include or ex-
clude. Accepted articles and articles we were still uncertain met
the inc lus ion criteria afte r titl e/ab stra c t screening ad vanced to the
full- text review. A total of 180 articles entered full- tex t screening.
During full- text screening, we excluded a further 113 articles. The
primary reasons for exclusion were the presence of some lethal
predator control (n = 30), the absence of a suitable measurement
of nest success (n = 16) and the absence of a suitable control group
(n = 16; Figure S1 and Appendix S3). Additionally, we excluded
parts of some relevant articles due to their lack of suitability for
the meta- analysis. We deemed 67 articles to fulfil all our inclusion
criteria (Figure S1).
During the literature screen, we flagged five relevant review
articles (Beauchamp et al., 1996; Franks et al., 2018; Hartway
& Mills, 2012; Scopel & Diamond, 2017; Smith et al., 2011) and
searched their reference lists for articles not found in the structured
literature search. We also searched the reference and citation lists
of the papers identified as suitable for our review in Covidence be-
tween the 12th and 13th of October 2023. We identified 13 articles
for inclusion through citation searching, bringing the total number of
articles included in our meta- analysis to 80 (Figure S1, Appendix S2).
2.4 | Data extraction and effect size calculation
We extracted data manually for 80 articles that met all inclusion
criteria. Whenever possible, we separated article components that
presented data on different prey families, different interventions
or used notably different methods. We refer to these components
within an article as ‘study units’ throughout the analysis. To pro-
vide a general overview of the literature, we extracted the country
in which the study took place, details of treatment and controls in
terms of protection measures implemented and sample sizes, as well
as re levant notes on study design and additional comments/assump-
tions. We extracted quantitative data to calculate an effect size (log
odds ratio) and corresponding sampling variance for each study unit.
See Appendix S1 for further detail regarding effect size calculations.
We predicted that five moderator variables would impact the
effectiveness of non- lethal nest protection interventions and ex-
tracted information accordingly (Table S1):
2.4.1 | Prediction 1—Intervention type
We predicted that physical barriers preventing predator access to
nests from all directions would be more effective than those which
only prevent access from a single direction and those that do not
physically prevent access at all (Prediction 1a). We categorised each
non- lethal nest protection intervention as either a physic al inter ven-
tion (exclosure, fence, guard) or a behavioural intervention (deter-
rent, conditioned taste aversion [CTA], diversionary feeding [DF] or
chemical camouflage [CC]). Two interventions that did not fit into
these categories (Mulder et al., 2021; Stojanovic et al., 2019) were
grouped as ‘other’. We defined an exclosure as a physical barrier
aiming to prevent predator access from all directions, a fence as a
physical barrier attempting to prevent the horizontal movement of
predators (accompanied by live- trapping and translocation for four
stud ies) and a gu ard as a phys ical barrier at tempt ing to prevent ver ti-
cal movement through climbing. Behavioural interventions aimed to
discourage nest predation by manipulating predator behaviour but
did not physically block their access to nests. We defined a deterrent
as an intervention that attempts to immediately discourage preda-
tors from predating a nest, conditioned taste aversion as an inter-
vention which involved conditioning predators to avoid consuming
eggs, diversionary feeding as the use of supplementary food to di-
vert predators away from nests and chemical camouflage as the use
of misleading odours to confuse olfactory predators into perceiv-
ing nests as unprofitable. Furthermore, we predicted that electri-
fied fences would have a stronger effect than non- electrified fences
(Prediction 1b) and therefore recorded whether fences were electri-
fied or not. Because just one study involved electrified exclosures
(Maslo & Lockwood, 2009), we only analysed the efficacy of electri-
fication for fences.
2.4.2 | Prediction 2—Nest position
We predicted that position of nests would influence the effective-
ness of interventions; specifically, that protection of ground nests
would be more effective than of nests in other locations, based
on the challenges associated with protecting less accessible nests
(Major et al., 2015). To test this, we recorded the nest position for
each study unit as a three- level factor: ground, elevated or cavity.
We defined a ground nest as any nest that was established on the
ground; an elevated nest as any nest elevated off the ground but
exposed to predators (e.g. cup nests); and a cavity nest as a nest
that is also off the ground but established in cavities such as tree
hollows or nest boxes. One study included nests from multiple posi-
tions (Cocquelet et al., 2019), and therefore we excluded it from the
analysis of this moderator.

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2.4.3 | Prediction 3—Predator taxon
We predicted that the predator taxon being targeted by an interven-
tion would influence the effectiveness of the intervention method.
To test this , we categorised each study as focusing on one of five dif-
ferent predator taxa: mammals, birds, reptiles, crustaceans or multi-
ple (protecting against more than one predator taxon).
2.4.4 | Prediction 4—Experiment type (artificial/
natural)
We predicted that artificial nest experiments could exhibit different
results to experiments focused on real nests, based on the diver-
gence of results from artificial and natural nests in previous stud-
ies (Moore & Robinson, 2004; Weston et al., 2017). To test this, we
defined each study unit as either artificial or natural based on the
nature of the experiment. One study combined artificial and natural
nests (Crabtree & Wolfe, 1988), and therefore we excluded it from
the analysis of this moderator.
2.4.5 | Prediction 5—Prey family
We predicted that the focal prey species could affect the effective-
ness of nest protection due to differences in life histories. Thus, we
controlled for bird family in our analysis. Some studies focused on
multiple bird species/families and therefore we could not always as-
sign a single family value for analysis. For artificial nest experiments,
we considered the species and family information not to be applica-
ble (N/A).
We recorded four additional methodological covariates to en-
sure that differences in approach did not explain the variation in
effect sizes between studies. These were study duration (number
of breeding seasons); whether nest success was defined as a binary
outcome (apparent nest success) or a rate (e.g. DSR); the period over
which nest success was measured (e.g. incubation period); and nest
failure definition (whether all causes of nest failure were considered,
or only failures due to predation). When this information was not
explicitly stated by the authors, we deduced the most logical value
where possible. Where this was not possible, we set this covariate
to N/A.
2.5 | Data analysis
Our complete data set consisted of 104 effect sizes (study units)
from 80 articles. As not all variables were available for all study
units, to test some predictions we divided the data into subsets
(Table S1). We used R v4.3.1 (R Core Team, 2022) for all data analy-
sis. We used the package metafor v4.4.0 (Viechtbauer, 2010) to cal-
culate effect sizes for each of our study units in the form of log odds
ratios and corresponding sampling variances (see Appendix S1 for
further details). We then fitted a random- effects model (null) and
mixed- effect models for these data, containing variables of interest
as single explanatory variables (intervention type, nest position, tar-
get predator taxon, experiment type and prey family). For a subset of
study units that involved fences, we tested the effect of electrifica-
tion using a mixed- effects model. Chi- squared tests revealed a lack
of independence between moderators (Table S2), so we did not fit
multivariate models to avoid multicollinearity (Graham, 2003). We
determined the most parsimonious model through comparison of
corrected Akaike information criterion (AICc) values, with the low-
est AICc value as the best fit to the data (Burnham et al., 20 11). We
fitted additional mixed- effect models to determine whether study
duration, nest success measurement type (binary or rate), nesting
period measured or failure definition had a measurable impact on
effect sizes.
To ensure our results were not biased by particular nuances of
the study set, we analysed two additional data sets. These contained
no more than two study units per article (achieved by combining
similar interventions or prey families where necessary, n = 92), and
all study units except those focused on piping plovers Charadrius
melodus (n = 89), as this species was disproportionately represented
in the global data set. To conduct a sensitivity analysis, we used the
leave1out() function in the package metafor (Viechtbauer, 2010),
which tests the effect of excluding any one study unit on the overall
model estimates. The analysis can be reproduced using the infor-
mation, code and data available at h t t p s : / / d o i . o r g / 1 0 . 5 2 8 1 / z e n o d o .
1070316 6 (Gautschi et al., 2024).
3 | RESULTS
3.1 | Global trends of non- lethal bird nest
protection research
The 80 articles included in the meta- analysis involved study sites in
20 countries and one overseas territory (Figure 1a). Over half (46)
were conducted in Nor th Ame rica. Nearly a third (31%) of articles in-
volved plover species (family Charadriidae), with 13 articles focusing
on piping plovers Charadrius melodus. The nests of a further 21 fami-
li e s (Figure 1b) and 64 species were represented in the meta- analysis,
of which only the giant ibis Thaumatibis gigantea is listed as Critically
Endangered and only the saffron- cowled blackbird Xanthopsar flavus
as Endangered according to IUCN criteria (IUCN, 2022). Only three
species are Vulnerable, while all others are either Near Threatened
(n = 4) or Least Concern (n = 56, Table S3).
Most articles (76%) were published in the 21st century. The me-
dian treatment duration for study units was one season (range 1–18
seasons, Figure 1c), and the median sample size of the treatment
group was 41.5 nests (range: 5–6767, Figure 1d). Median control
sample size was 56.5 nests (range: 5–4538, Figure 1d).
Exclosures and fences were the most commonly used nest pro-
tection measures (Figure 2a). Five articles tested more than one type
of predator intervention method, either together (n = 2) or separately

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(n = 3). Nearly half (49%) of the articles focused on at least two pred-
ator taxa, including a combination of mammals, birds and reptiles
(Figure 2b). More than three quarters (76%) of articles focused on
ground- nesting birds (Figure 2c). A total of 56 articles measured the
effectiveness of non- lethal nest protection interventions using nat-
ural nests, 21 conducted artificial nest experiments and three in-
cluded both artificial and natural nest components (Figure 2d).
3.2 | Efficacy of non- lethal nest
protection methods
Overall, non- lethal nest protection significantly improved nest
success relative to unprotected control nests (model esti-
mate = 1.02; 95% CI = 0.79–1.24 based on 104 effect sizes from
80 articles). Of the moderators tested, only intervention type
(Prediction 1a, n = 104 effect sizes), target predators (Prediction
3, n = 104) and prey family (Prediction 5, n = 68) had a signifi-
cant impact on the effectiveness of non- lethal nest protection
(Figure 3a,c,f). Experiment type (Prediction 4, n = 103) and nest
position (Prediction 2, n = 103) did not have a significant impact.
Treatments had a positive impact on nest success when applied
to both artificial and natural nests, and when dealing with cavity,
elevated and ground nest s (Figure 3b,d). Exclosures were the most
ef fectiv e int e r ven t ion in terms of in cre asi ng nest succe ss, fol low ed
by a combination of fences and exclosures, fences, and guards.
Both electric and non- electric fences showed a positive effect on
nest success (Prediction 1b, n = 27, Figure 3e). Interventions clas-
sified as chemical camouflage, conditioned taste aversion, deter-
rent, diversionary feeding or ‘other’ did not significantly improve
FIGURE 1 (a) Non- lethal nest protection articles included in this meta- analysis (n = 80) by country. Note two articles involved study
sites in both Canada and USA. (b) Bird prey families by the number of articles in which they are represented. (c) Study units by duration in
breeding seasons (n = 104) and (d) Control size versus treatment size (in nests) of study units (n = 104). The information presented includes
only peer- reviewed studies in English.

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nest success (Figure 3a, Table S4). Overall, physical interventions
(n = 73) were significantly more effective than behavioural inter-
ventions (n = 31; Figure 4). Treatments had a significant positive
impact on nests success when protecting against birds, mammals
and multiple predator taxa, but not when protecting against rep-
tiles or crustaceans (Figure 3c). Only nest treatments involving
the nests of plovers (Charadriidae), sandpipers (Scolopacidae) and
Australasian robins (Petroicidae) showed a significant positive ef-
fect on nest success (Figure 3f, Table S4). The most parsimonious
model explaining nest success included intervention type as the
only explanatory variable (∆AICc = − 29.9, Table S5). Support for
the most parsimonious model did not change when we excluded
piping plover studies or excessive study units (>2) from any one
article (Table S6). Methodological variables tested (study duration,
nest success measurement type [binary or rate], nesting period
measured and failure definition) did not have a significant impact
on effect size when added to the best model (Table S7).
Our results did not vary significantly for the two restricted data
sets tested (Table S6) or when using the leave1out() function to test
the sensitivity of the model to the removal of individual studies
(Table S8).
4 | DISCUSSION
Implementing conservation actions based on robust evidence can
increase the success of interventions and limit costs (Sutherland
et al., 2004). Protecting breeding birds without the lethal control
of predators has been an increasing area of interest in the field of
wildlife management (Doherty & Ritchie, 2017; Smith et al., 2011).
Therefore, we conducted a global meta- analysis to examine the ef-
ficacy of non- lethal nest protection methods. We found that articles
that met our meta- analysis inclusion criteria were biased towards
certain regions, species, intervention types and nest characteristics.
Our results show that exclosures, fences and guards have a signifi-
cant positive impact on nest success and that prey family and target
predator taxon also have a significant impact on the effectiveness
of non- lethal nest protection interventions. We discuss the implica-
tions of our findings for improving future research and conservation
efforts.
4.1 | Trends in non- lethal bird nest protection
Most articles in our analysis involved physical barriers such as
predator exclosures, fences or guards. However, nearly a quarter
(24%) of the articles focused on behavioural interventions such
as deterrents and conditioned taste aversion. Almost all articles
(91%) focused on mammalian or mixed predator communities,
with very few attempting to specifically protect nests from other
taxa. This may reflect the particularly damaging impact of inva-
sive mammalian predators on bird species (Doherty et al., 2016).
However, it may also reflect an under- appreciation of the role of
non- mammalian predators in nest predation (Guppy et al., 2017),
FIGURE 2 Summary of the 80 articles included in this meta- analysis showing the division of articles by (a) intervention type; (b) target
predator taxon; (c) nest position; and (d) experiment type. CTA represents conditioned taste aversion; DF represents diversionary feeding;
and CC represents chemical camouflage. The information presented includes only peer- reviewed studies in English.

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FIGURE 3 Estimated model coefficients from mixed- effect models exploring the effectiveness of non- lethal nest protection efforts.
Each model contained one moderator with effect size as the response variable. (a) intervention type (study units n = 104); (b) nest position
(n = 103); (c) target predator taxon (n = 104); (d) experiment type (n = 103); (e) electrification of fences (n = 27); and (f) nesting prey family
(n = 68). Error bars represent 95% confidence inter vals. Zero is indicated by the dashed line and error bars that do not overlap zero indicate a
significant positive or negative effect.

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or the increased difficulty in protecting nests from such species.
Furthermore, many articles did not discuss target predators in de-
tail (e.g. Bailey & Bonter, 2017; Mulder et al., 2021), suggesting
that in some cases there may have been a lack of consideration for
the identity of key nest predators.
Non- lethal nest protection experiments have historically been
biased towards North America, where a great deal of work has
been done on two species in particular: the piping plover and
snowy plover Charadrius nivosus. However, in the last 10 years, 24
of 31 relevant articles focused on other continents, suggesting
that this spatial bias is decreasing. Nearly a third (31%) of articles
involved the family Charadriidae, which is probably due to the long
history of successful use of nest protection measures reported by
researchers working on plovers (e.g., Rimmer & Deblinger, 1990).
Although 22 bird families and 65 species were represented in
our review, only two articles involved species listed as either
Endangered or Critically Endangered by the IUCN (IUCN, 2022).
This does not consider the status of local populations or subspe-
cies, which may not be reflected in the IUCN rating. Furthermore,
it is acknowledged that the articles included in this review had
varying motivations. While some were clearly focused on con-
servation (e.g., Pucheta et al., 2018), other articles had different
motives such as understanding the role of certain predators (e.g.
Cocquelet et al., 2019) or examining the anti- predatory strategies
employed by nesting birds (Liu & Liang, 2021). In addition, some
studies used a non- threatened species to test an experimental
nest protection measure intended for a conservation application
(e.g. Stojanovic et al., 2019). While the poor representation of
threatened species in this review is surprising, threatened species
may be poor subjects for experimental studies if their small pop-
ulation sizes hinder statistical inference or if fear of negative out-
comes prevents management action (Canessa et al., 2020).
More than three quarters (76%) of articles focused on ground-
nesting species. This trend could reflect the fact that ground-
nesting birds are disproportionately in decline and threatened by
predators (Ekanayake et al., 2015; McMahon et al., 2020; Roos
et al., 2018) and are therefore more likely to be the subject of nest
protection efforts. However, it could also reflect a bias in con-
servation efforts in favour of ground- nesting species, whereby
ground nests are easier to find, monitor and protect, relative to
arboreal nesting species. While non- lethal nest protection for ar-
boreal nesting species using cavities or cup nests was much less
common, it appears to be increasing. Articles involving these nest
types (n = 19) were more globally distributed than those involving
ground nests, with more studies taking place in Australia (32%)
and Asia (26%) than North America (16%).
Nearly a third (30%) of articles used artificial nest experiments to
test the effectiveness of non- lethal nest protection. Artificial nest ex-
periments have made significant contributions to our understanding
of nest predation (Major & Kendal, 1996). Some of the experiments
included in our sample may not have been possible without the use of
artificial nests due to the difficulty of obtaining a sufficient sample of
natural nests (e.g. Canessa et al., 2020), and often provided for more
suitable experimental conditions. However, the reliability of artificial
nest studies in the context of comparable natural nest s remains a mat-
ter of debate (Moore & Robinson, 2004; Weston et al., 2017 ).
Most study units (51%) were conducted over a single breeding sea-
son. This is concerning in terms of drawing evidence- based conclusions
to inform management. In many environments, nest survival rates can
vary annually contingent on multiple, often correlated factors including
weather, vegetation growth and predator abundance cycles (Moynahan
et al., 2007; Winter et al., 2005). Similarly, most treatment sample sizes
were relatively small, with 73% of study units having a treatment sam-
ple of less than 100 nests. Most of the study units using natural nests
used the incubation period as their preferred measurement period
(n = 45), rather than the full nesting period (n = 21) or defined success
as survival over a number of days (n = 4). One natural nest study mea-
sured success during only the nestling stage (Pucheta et al., 2018). The
artificial nest study timeframes were often based on a biologically rel-
evant period (e.g. incubation period, Canessa et al., 2020), but this was
not always the case (e.g. 6 days, Liu & Liang, 2021). Wherever possible,
we included figures that reflected overall nest failures rather than only
failures due to predation, as this most accurately reflects the impact of
non- lethal nest protection on nest success. For example, while protec-
tion against nest predators may reduce nest predation, it may also lead
to an increase in nest abandonments (Barber et al., 2010). A total of
83% of study units using natural nests presented data that considered
nest failures beyond predation.
FIGURE 4 Estimated model coefficient from a mixed- effect model exploring the effectiveness of non- lethal nest protection efforts by
intervention class; physical interventions (n = 73) and behavioural interventions (n = 31). Error bars represent 95% confidence intervals. Zero
is indicated by the dashed line and error bars that do not overlap zero indicate a significant positive or negative effect.

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4.2 | Effect of interventions on nest success
Our results show that non- lethal physical interventions generally
improve nest success for birds. Predator exclosures and fences were
the most effective interventions, but combinations of the two were
no more effective than either method used independently. Guards,
which prevent the vertical travel of predators (and are therefore only
applicable to arboreal nesting species) also significantly increased
nesting success.
Overall, behavioural interventions show a positive impact on nest
success, however modelled confidence limits overlapped zero. The
smaller number of studies using these interventions, particularly chem-
ical camouflage (n = 2) and diversionary feeding (n = 5), limited the con-
fidence of model estimates. Conditioned taste aversion and deterrents
were also diverse in nature, employing various conditioning agents and
comprising scent, sound and vision- based approaches, but the num-
ber of studies that used such treatments were too small to evaluate
independently. While behavioural interventions show promise (e.g.
Norbury et al., 2021; Selonen et al., 2022), there is currently insuffi-
cient evidence to conclude whether they are reliable nest protection
methods and the effectiveness of such approaches may be highly
context- specific, for example using snake slough to deter Swinhoe's
striped squirrels Tamiops swinhoei from nest boxes (Liu & Liang, 2021).
Target predator and prey taxa also appeared to influence the ef-
fectiveness of nest protection interventions. Efforts focused on pre-
venting predation by reptiles or crustaceans did not show a significant
positive effect on nest success, though the combined sample size was
small (n = 3). Interventions focused on protection of nests against birds,
mammals or a mixed predator community were effective, but only
those focused on three prey families (Charadriidae, Scolopacidae and
Petroicidae) had a significant positive impact on nest success. This can
be partly explained by the larger number of study units for Charadriidae
(n = 26) and Scolopacidae (n = 6) allowing for narrower confidence in-
tervals for these families. Conversely, only one study focused on the
family Petroicidae, finding that a small number of exclosures (n = 7)
were highly effective at reducing predation (Debus, 2006). The finding
that studies on other families did not show a significant positive model
estimate is probably explained by the small number of study units rep-
resenting other families (median: 1, range: 1–9). Surprisingly, we also
found that electric fences (n = 18) were no better at improving nest
success than non- electric fences (n = 9), with the data suggesting they
may be worse. Studies involving electric fences often commented on
their inability to exclude all predators in mixed predator communities
and fence breaches caused by power issues (e.g. Conner et al., 2010;
LaGrange et al., 1995 ). We recommend further experiments to refine
electric fencing as a non- lethal nest protection measure.
4.3 | Study limitations
Given the varied environments in which wild bird nest protection ex-
periments were conducted and a lack of clear methodological guide-
lines for nest protection experiments, the studies included in our
meta- analysis vary in their approaches. Most variation is dictated by
the focal prey species, the type and position of nest used and inherent
specificities of the study systems. In addition, many studies occurring
as part of management actions have imperfect experimental designs.
Ho wev er, thi s does not pre clude them fr om pro d ucin g valu able insig hts
to inform adaptive management. To avoid constraining our sample, we
included studies that measured nest success in terms of daily survival
rate or apparent nest success. We also accepted studies that counted
only predated nests as unsuccessful, as well as studies that included all
causes of failure in the control and treatment groups. Multiple periods
of measurement for nest success were accepted (incubation period,
full nesting period or survival over a pre- determined period). Because
all these factors could influence our results, we added these variables
into the most parsimonious model to determine whether they had a
significant influence on the effect size for each study unit. The results
suggest that these methodological variables did not explain the effec-
tiveness reported. While consistent methodologies would make stud-
ies more comparable, we considered the inclusion of a wide variety of
non- lethal nest protection studies to be of greater importance.
For this review, we did not consider lethal nest protection or hab-
itat manipulation measures used to reduce predation. As a result, we
do not asse ss the efficacy of these nest protec tion measures her e, sug-
gesting separate meta- analyses are warranted for these approaches.
We attempted to identify all available peer- reviewed literature that
met our criteria; however, we probably omitted some relevant articles.
For instance, due to language constraints, our search string only in-
cluded English search terms and we only considered articles for which
the full text was available in English, potentially overlooking some stud-
ies and/or introducing a geographical bias. The importance of breaking
down language barriers is increasingly being recognised in ecology and
conservation (Negret et al., 2022), so broadening our analysis across
multiple languages should become more viable in the near future. We
also only considered research published in peer- reviewed journals.
We took this approach to ensure repeatability, but we acknowledge
that this risks overlooking potentially important evidence in the grey
literature (Haddaway & Bayliss, 2015) and also the potential for under-
representation of negative findings as a result (Mlinarić et al., 2 017).
However, our data are available online (Gautschi et al., 2024) and
could be further extended with data from other languages and grey
literature.
4.4 | Conservation implications and
recommendations for future research
Non- lethal nest protection is becoming an increasingly impor-
tant area of research given the potential of such methods to yield
longer- term and more cost- effective conservation outcomes.
The applicability of our findings also extends beyond birds to
other nesting taxa facing elevated predation rates such as turtles
(O'Connor et al., 2017) and freshwater crocodiles (Somaweera
et al., 2011). Our sys tema tic se arch reve aled man y rele vant st udi e s
that could not be included due to a lack of suitable experimental

1196
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conditions, the simultaneous use of lethal predator control or a
focus on threats other than predation. To thoroughly examine the
efficacy of non- lethal nest protection interventions, experiments
should ideally be performed independent of lethal predator con-
trol and the treatment group should be contrasted with a com-
parable control group. While funding and other limitations may
prevent multiple years of experimentation, we also encourage re-
searchers to undertake longer- term studies whenever possible, as
this would allow for temporal replication and greater confidence
in results (Johnson, 2002).
It is encouraging to see an increasingly global distribution of
peer- reviewed articles as well as more articles dealing with novel
protection techniques and different species. However, there is still
a need for further studies on cup and hollow- nesting birds which
are currently under- represented in the conservation literature. For
example, songbirds (order Passeriformes) comprise 60% of global
bird diversity (Ericson et al., 2003) yet were included in only 20% of
articles using natural nests in our analysis.
A crucial first step in effective nest protection is to obtain a
thorough understanding of the predators posing a threat to nesting
birds. Passive monitoring studies are increasingly showing that nest
predator assemblages are often more diverse than may be assumed
(Guppy et al., 2017 ). To avoid compensatory predation by other
species (Ellis- Felege et al., 2012), non- lethal methods should be de-
signed as much as possible to protect against the entire predator
assemblage.
Our res ult s provi de cau tio us opt imism fo r the us e of non - l eth al
nest protection to reduce predation. Non- lethal nest protection
interventions can be effective at increasing nest success and can
have profound impacts on the breeding success of wild birds (e.g.
Maslo & Lockwood, 2009; Norbury et al., 2021; Tan et al., 2015).
Despite the value of non- lethal interventions, lethal predator
control should not be discounted when considering management
options (Smith et al., 2010). With either approach, managers and
researchers must consider predator interventions in the context
of other factors such as habit at quality and predator abundance as
these are likely to interact with one another (Douglas et al., 2023).
When considering the suitability of non- lethal predator control,
managers and researchers should determine (i) what the exact
ai ms of pote ntia l nest protection inte rventions a re; an d (ii) whether
these techniques are suitable for their system. Managers should
also consider whether nest protection efforts can be practically
implemented at a sufficient scale to have a noticeable impact on
the overall breeding output of a population, if that is the overall
conservation goal. Alongside these considerations, our findings
can contribute to evidence- based decision- making, increasing the
chances of wild bird nesting success and reducing unnecessary
ethical and financial costs in the process.
AUTHOR CONTRIBUTIONS
Da ni el G a ut sc h i, R o ss C ra te s, R o be rt He in so hn a nd A nt ic a Ču li na co n-
ceived and designed the research; Daniel Gautschi and Ross Crates
conducted the title/abstract screening; Daniel Gautschi performed
the full- text screening and data extraction; Daniel Gautschi, Ross
Crates and Antica Čulina conducted the meta- analysis; Daniel
Gautschi, Ross Crates, Antica Čulina, Robert Heinsohn and Dejan
Stojanovic wrote and edited the manuscript. All authors contributed
critically to the drafts and gave final approval for publication.
ACKNOWLEDGEMENT
This study was funded by an ANU Fenner School of Environment
and Society PhD Scholarship. Open access publishing facilitated
by Australian National University, as part of the Wiley - Australian
National University agreement via the Council of Australian
University Librarians.
CONFLICT OF INTEREST STATEMENT
We have no conflicts of interest to disclose.
DATA AVAILAB ILITY STATEMEN T
Data and code are available from Zenodo h t t p s : / / d o i . o r g / 1 0 . 5 2 8 1 /
zenodo. 10703166 (Gautschi et al., 2024).
ORCID
Daniel Gautschi https://orcid.org/0000-0002-0215-5685
Antica Čulina https://orcid.org/0000-0003-2910-8085
Robert Heinsohn https://orcid.org/0000-0002-2514-9448
Dejan Stojanovic https://orcid.org/0000-0002-1176-3244
Ross Crates https://orcid.org/0000-0002-7660-309X
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SUPPORTING INFORMATION
Additional supporting information can be found online in the
Supporting Information section at the end of this article.
Table S1. Predictions associated with moderator variables and the
sample sizes included in the meta- analysis.
Table S2. Results of Chi- square ( χ2) tests showing correlation
between variables of interest. p- values are shown in parentheses.
Table S3. Prey species whose nests were included in the meta-
analysis by 2023 IUCN Red List status.
Table S4. Estimated model coefficients from mixed effect models
including moderator variables, with the log odds ratio of nest success
treatments as the response variable.
Table S5. Results of mixed effect models containing moderator
variables with the effectiveness of interventions in increasing nest
success as the response variable.
Table S6. Results of mixed effect models containing moderator
variables with the effectiveness of interventions in increasing nest
success as the response variable, for restricted data sets.
Table S7. Estimated model coefficients from multivariate mixed effect
models including intervention type and a single methodological
variable as predictor variables and the log odds ratio of nest success
treatments as the response variable.
Table S8. Estimated model coefficients produced using the
leave1out() function in the R package metafor.
Figure S1. PRISMA flow diagram showing results of the literature
search, title/abstract screening, full- text screening and citation search.
Appendix S1. Supplementary Methods.
Appendix S2. Reference list of articles included in the met a- analysis.
Appendix S3. Details of studies excluded during full- text review.
How to cite this article: Gautschi, D., Čulina, A., Heinsohn,
R., Stojanovic, D., & Crates, R. (2024). Protecting wild bird
nests against predators: A systematic review and meta-
analysis of non- lethal methods. Journal of Applied Ecology, 61,
1187–1198. ht tps://doi.org/10.1111/1365-266 4.14619