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DOC RESEARCH AND DEVELOPMENT SERIES 365
Potential factors aecting the calling
rates and detectability of crake and rail
species: a review
Emma M. Williams
2020
DOC Research & Development Series is a published record of scientific research carried out, or advice given, by Department of Conservation
sta or external contractors funded by DOC. It comprises reports and short communications that are peer-reviewed.
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© Copyright May 2021, New Zealand Department of Conservation
ISSN 1177–9306 (web PDF)
ISBN 978–0–9951392–7–5 (web PDF)
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CONTENTS
Abstract 1
1. Introduction 2
2. Methods 3
3. Variables associated with calling rates in crakes and rails 4
3.1 Temporal variables 4
3.1.1 Time of day 4
3.1.2 Time of year 4
3.1.3 Year 6
3.2 Environmental variables 6
3.3 Population demographics / biological variables 7
3.4 Nuisance variables 9
3.5 Interactive variables 9
4. Implications for monitoring New Zealand crakes and rails 10
5. Acknowledgements 11
6. References 11
Appendix 1
Scientific name and IUCN classification of the species examined 15
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DOC Research and Development Series 365
Potential factors aecting the calling rates
and detectability of crake and rail species:
a review
Emma M. Williams
Department of Conservation, Private Bag 4715, Christchurch 8140, New Zealand.
Email: emwilliams@doc.govt.nz
Abstract
Wetlands provide habitat for some of New Zealand’s most secretive and dicult to detect
threatened bird species, including crakes and rails (family Rallidae). However, it is currently
dicult to measure population trends for these birds in relation to conservation management
activities due to a lack of standard monitoring methods. This report reviews the use of call-count
methods for surveying and monitoring members of the family Rallidae worldwide to determine
whether they could form the basis for developing monitoring techniques in New Zealand. This
review shows that common covariates that influence the calling rates, and thus the detectability
of crakes and rails, include: temporal variables (time of day, time of year and year), environmental
variables (moon phase, moon light, cloud cover, rainfall, wind speed, temperature, date of last
natural disturbance, water level, tidal stage and salinity content), variables relating to population
demographics (sex of bird, reproductive status/stage, migratory behaviour and population
density), ‘nuisance’ variables (location, observer disturbance and background noise) and four
potential interactions between these. These variables could be accounted for in monitoring
programmes by undertaking repeat counts under standardised conditions or recording all
relevant variables to allow their eects to be corrected for during later analysis. Future research
should quantify the eects of these variables on the calling rates and detection probabilities
of New Zealand crakes and rails to develop monitoring methods that are best suited to our
wetlands.
Keywords: inventory, monitoring, wetland birds, conservation management, call counts,
threatened species, crakes, rails, Rallidae, New Zealand.
© Copyright May 2021, Department of Conservation. This paper may be cited as: Williams, E.M. 2021: Potential factors
aecting the calling rates and detectability of crake and rail species: a review. DOC Research and Development
Series 365. Department of Conservation, Wellington. 17 p.
2Williams— Factors aecting the calling rates and detectability of crake and rail species
1. Introduction
Call-count-based methods are commonly the only methods available for detecting cryptic
species, i.e. those species that are secretive, well-hidden and/or located in inaccessible areas
(Williams 2016). However, there are many examples where call-count-based methods have
insucient power to be useful as index methods (e.g. Clarke et al. 2003), which is particularly
likely when detectability is aected by variables that are also hard to detect (as is the case for
cryptic species by definition).
Small sample sizes and low/variable detections limit the inferences that can be made about
cryptic species populations, making it unlikely that low-precision methods such as indices will
be useful for measuring them (Williams 2016). Consequently, many authors argue, quite rightly,
that under these circumstances monitoring methods that can measure or account for changes in
detectability should be used so that the number of individuals that were not detected can also be
estimated (Alldredge et al. 2007; Diefenbach et al. 2003; Farnsworth et al. 2002; Royle & Nichols
2003). However, to do this, managers must first identify which variables are likely to aect
detectability and quantify these eects (Williams et al. 2018).
New Zealand wetlands provide habitat for some of the country’s most cryptic threatened
species, including the Australasian bittern (matuku, Botaurus poiciloptilus) (Fig. 1), marsh crake
(koitareke, Porzana pusilla/Zapornia pusilla) (Fig. 2) and spotless crake (pūweto, P. tabuensis/
Z. tabuensis) (Fig. 3). However, these habitats currently occupy less than 10% of their historic
range (Cromarty & Scott 1996; Ausseil et al. 2011) and little is known about how this loss of
habitat has aected these bird species. Therefore, there is a need to develop monitoring methods
for cryptic wetland bird species that can a) determine their status, distribution and threats;
b) identify and protect their key sites; and c) measure the responses of their populations to
conservation management practices.
Development of inventory and monitoring techniques for New Zealand’s crakes and rails (family
Rallidae) is likely to start with development of call-based methods initially. This is because bird
calls provide distinct cues that can be detected even when the individual is hidden in thick
vegetation and call-based methods generally require less development compared with other
potential techniques (such as thermal imagery, the use of dogs and camera traps) before they can
be used.
Some progress has already been made in identifying the factors that aect the call rate of
Australasian bitterns (Williams 2016; Williams et al. 2018), which has led to the development of
monitoring methods that can be used on males of this species (O’Donnell et al. 2013; O’Donnell &
Williams 2015;). However, while male bitterns represent a great flagship species for wetlands, they
are not entirely suitable as indicator or surrogate species that can show representative population
changes in response to management practices.
For example, adult male bitterns are sizable,
aggressive and have large seasonal home
ranges that span multiple wetlands (EMW
unpubl. data), suggesting that they will be
less vulnerable to site-specific threats such
as invasive predators than smaller crake-like
species. Consequently, male bitterns may be
less sensitive and therefore less informative
with regard to management changes that are
being applied at a local level.
Figure 1. Australasian bittern (matuku). Photo: M.F. Soper
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DOC Research and Development Series 365
Crakes and rails inhabit the same habitats as bitterns but are sensitive to all invasive predator
species and produce multiple clutches per season (O’Donnell et al. 2015). Consequently,
populations of these birds may have the capacity to change more rapidly than bitterns,
potentially making their population changes a better indicator of short-term management
outcomes. Therefore, there is a need to identify and quantify any variables that may influence the
call-based detectability of New Zealand crake and rail species.
This report reviews published articles on the use of call-count methods to survey and monitor
members of the Rallidae family worldwide to assess their suitability for forming a basis for the
development of techniques in New Zealand. In particular, the study examined which variables
are likely to aect the behaviours and detectability of New Zealand crake and rail species to
determine the optimal times and conditions for monitoring these threatened species and to
develop general monitoring protocols for wetland bird species.
2. Methods
Peer-reviewed articles on the family Rallidae were located by searching Google Scholar for each
genus using the search terms ‘call’ and ‘vocalisation’. This yielded 61 articles that discussed
the calling rates of 45 of the 137 species in this family (Appendix 1). For each article, any
variables that were reported were classified into one of three subjective categories for each
species discussed: × if the publication tested the variable but no eect was apparent; if the
publication tested the variable and the results suggested that an eect existed; and ? if the
publication reported on the variable speculatively or if the variable was tested but the results
were ambiguous. Of the 45 species examined, the best-studied species were the sora (P. carolina;
n = 18), black rail (Laterallus jamaicensis; n = 17), Virginia rail (Rallus limicola; n = 14), clapper rail
(R. crepitans; n = 11), king rail (R. elegans; n = 6), yellow rail (Coturnicops noveboracensis; n = 6)
and common moorhen (Gallinula chloropus; n = 6).1 For all other species, there were less than five
publications per species.
To provide a simple assessment of how widely a variable was reported, the percentage of
species that each variable was attributed to was calculated. These reporting rates represent the
percentage of species examined (i.e. out of the 45 species for which information could be found)
that had some information regarding that variable (regardless of the trend or any ambiguity).
Figure 2. Marsh crake (koitareke). Photo: Emma Williams
Figure 3. Spotless crake (pūweto),
Photo: Geoffrey Dabb
1. Note: The total number of publications per species does not equal the total number of publications reviewed because several
publications provided information on multiple species.
4Williams— Factors aecting the calling rates and detectability of crake and rail species
3. Variables associated with calling rates in
crakes and rails
A wide variety of variables were suggested as potentially aecting the calling rates of members
of the Rallidae family. These included three temporal variables (time of day, time of year and
year), ten environmental variables (moon phase, moon light, cloud cover, rainfall, wind speed,
temperature, date of last natural disturbance, water level, tidal stage and salinity content), four
variables relating to population demographics (sex of bird, reproductive status/stage, migratory
behaviour and population density), three nuisance variables (location, observer disturbance
and background noise) and four interactive eects. In addition, the use of playback was often
recommended for monitoring Rallidae species to increase their detectability (Ribic et al. 1999).
In general, temporal variables were associated with the highest percentage of species (reporting
rate = 60%), followed by several population demographic variables (reporting rate = 42%) and
variables associated with the use of playback (reporting rate = 38%). All other variables were
reported or discussed in fewer than five publications.
3.1 Temporal variables
3.1.1 Time of day
Among the three temporal variables that have been identified, time of day appeared to aect
the largest number of species (21 species, reporting rate = 47%; Table 1). However, the exact
relationship between the time of day and calling rate is unclear. For example, Ripley (1977)
stated that Rallidae species call ‘more commonly in early mornings or evenings but sometimes
during day and night’, suggesting that diurnal trends may be appropriately classified into daily
periods. Indeed, peak calling periods that corresponded to a particular time period (i.e. morning,
evening or night) were most commonly reported (18 publications, reporting rate = 38%). However,
Conway (2009; 2011) suggested that Rallidae calls peak in relation to sunrise and sunset,
which was supported by nine of the publications included in this review (10 species, reporting
rate = 22%). Regardless of the relationship reported, none of the publications reviewed here
tested both relationships within the same study, making it dicult to determine whether their
results reflected true relationships or were a product of what was tested. Only one study oered a
biological explanation for these diurnal patterns – Akhtar et al. (2015) suggested that the calling
rate of the white-breasted waterhen (Amaurornis phoenicurus) peaked in the early morning
when individuals were actively searching for food and so concluded that these calls represented
attempts to communicate the individual’s intentions/findings regarding food to conspecifics.
3.1.2 Time of year
The time of year (usually reported by month) also appeared to be an important variable to
consider, being reported for 12 of the 45 species (reporting rate = 27%; Table 1). However, most
time of year eects appeared to coincide with or were near to the breeding season, suggesting
that they were related to the reproductive status and stage. For example, Polak (2005) found
that the calling rate of water rails (R. aquaticus) peaks in April and June, around the time of egg
laying, which is consistent with the postulation that these calls are associated with mate guarding
and mate attraction (Catchpole 2003; Cramp & Simmons cited in Ręk 2015). In addition, some
publications reported multiple peaks in calling across the year (Conway & Gibbs 2011), which
may have coincided with the production of multiple clutches or females becoming available
again for mating following nest failures.
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DOC Research and Development Series 365
A second possibility is that monthly peaks in calling rates are byproducts of migration (i.e. a
lack of calling is due to the absence of birds rather than a change in their detectability). Seasonal
migrations have been reported for yellow rails, red-necked crakes (Rallina tricolor), white-
throated crakes (L. albigularis), grey-breasted crakes (L. exilis) and azure gallinules (Porphyrio
flavirostris) (Harvey et al. 2014; Mittermeier et al. 2013; Reynard 1974; Stiles & Levey 1988; Taylor
1998). Like calling, the timing of these migratory behaviours will also be aected by a suite of
variables – for example, the migration of red-necked crakes, white-throated crakes and grey-
breasted crakes is linked with the wet season (Stiles & Levey 1988; Taylor 1998, pp. 54; Mittermeier
et al. 2013;). In general, seasonal migration patterns and the factors that aect the timing of these
have not been well studied in New Zealand or other countries for Rallidae species. Therefore,
more data on Rallidae movements would be useful for developing monitoring methods that use
calling rates as a surrogate for abundance.
SPECIES TIME TO
SUNRISE/
SUNSET
TIME OF DAY
(MORNING/
EVENING/NIGHT)
TIME OF YEAR YEAR
American coot ?g
American purple gallinule ?g
Austral rail ?z
Azure gallinule v
Black rail l; ?m,n xe,g,o,p; n,q,r,s e,n,s,t,u e,n,r
Buff-banded rail ?i?j
Clapper rail e,ab e,r
Common moorhen ?g?h
Corncrake ff
Grey-breasted crake k
King rail xg
Ocellated crake ?a
Plain bush-hen ?a
Red-legged crake ac ?z?z
Red-necked crake jj
Ruddy crake ?a
Slaty-legged crake ?ai; ?h
Sora xe,g e,d,w; ?a
Speckled crake ?c
Spotted crake y
Virginia rail e,d,w
Water rail aa
Watercock ?a
White-breasted waterhen bb
White-throated rail ?a
Yellow rail ?dd, xe
Yellow-breasted crake ?x
Number of references 918 15 3
Reporting rate 10 (22%) 17 (38%) 12 (27%) 2 (4%)
References: a Ripley (1977); b Akhtar et al. (2015); c Teixeira & Puga (1984); d Gibbs et al. (1991); e Conway & Gibbs (2011); f Mason (1950);
g Nadeau et al. (2008); h Lewthwaite & Yu (2001); i Pratt et al. (1980); j Mittermeier et al. (2013); k Stiles & Levey (1988); l Reynard (1974);
m Spautz et al. (2005); n Conway et al. (2004); o Spear et al. (1999); p Tecklin (1999); q Repking (1975); r Flores & Eddleman 1991 cited in
Conway & Gibbs 2011; s Legare et al. (1999); t Kerlinger & Wiedner (1991); u Repking & Ohmart (1977); v Smith et al. (2005); w Gibbs &
Melvin (1993); x Renaudier & de Guyane (2010); y Ręk (2015); z Barnet t et al. (2014); aa Polak (2005); ab Conway et al. (1993); ac Brazil (2009).
Table 1. Temporal variables reported in peer-reviewed publications for extant Rallidae
species. × = no effect, = effect detected, ? = effect ambiguous. Reporting rates represent the
percentage of species examined (i.e. out of the 45 species for which information could be found)
that had some information regarding that variable (regardless of the trend or any ambiguity).
Superscript letters indicate references (see footnote). See Appendix 1 for scientific names.
6Williams— Factors aecting the calling rates and detectability of crake and rail species
3.1.3 Year
Year was reported to aect the calling rate for 2 of the 45 species (reporting rate = 4%; Table 1).
The existence of a year eect is concerning as it indicates that calling rate is unpredictable or
is driven by factors that are dicult to measure or identify (and therefore will not be included
in models). However, given the high ambiguity of most variables and the lack of understanding
regarding the biological significance of calling, a reporting rate of 4% is reasonable (assuming
that most publications considered observations from multiple years, which is not stated in many
cases). Nevertheless, it would be prudent to collect call-rate data across multiple years and to test
for a year eect.
Table 2. Environmental variables reported in peer-reviewed publications for extant Rallidae
species. × = no effect, = effect detected, ? = effect ambiguous. No references could be found
for two potential variables, ‘date of last natural disturbance’ and ‘salinity content’. Reporting
rates represent the percentage of species examined (i.e. out of the 45 species for which
information could be found) that had some information regarding that variable (regardless of the
trend or any ambiguity). Superscript letters indicate references (see footnote). See Appendix 1
for scientific names.
References: a Akhtar et al. (2015); b Conway & Gibbs (2011); c Bart et al. (1984); d Nadeau et al. (2008); e Ripley (1977) ; f Spear et al. (1999);
g Reynard (1974); h Conway (2009); i Smith et al. (2005); j Jenkins & Ormerod (2002); k Zembal & Massey (1987); l Coates & Bishop (1997).
SPECIES MOON
PHASE
MOON
LIGHT
CLOUD
COVER
RAIN-
FALL
WIND
SPEED
TEMP. WATER
LEVELS
TIDAL
STAGE
American coot ?d
American purple gallinule ?d
Ash-throated crake ?i
Black rail xbb,f ?gb,f,h
Clapper rail ?d?d?db,h,k
Common moorhen ?d
King rail ?e
Mangrove rail ?e
Red-legged crake ?l
Rouget’s rail ?e?e
Virginia rail ?b?b?e
Water rail ?j?j
Watercock ?e?e
White-breasted waterhen a
Yellow rail xb,c
Number of references 23236125
Reporting rate 3 (7%) 3 (7%) 3 (7%) 3 (7%) 5 (11%) 4 (9%) 2 (4%) 3 (7%)
3.2 Environmental variables
Ten environmental variables were discussed in the literature. These included moon phase,
moonlight, cloud cover, rainfall, wind speed, temperature, water level, tidal stage, date of last
natural disturbance and salinity content (Table 2). Reports on most of these variables were
speculative, with a non-ambiguous relationship only being apparent for variable tidal stage,
which was reported to aect the calling rates of black rails (three publications) and clapper
rails (three publications) but was ambiguous for mangrove rail (R. longirostris; one publication)
(Table 2). No information was available on the biological significance of tidal stage, but Conway
(2009) speculated that nest success may be influenced by the timing of high tides.
Evidence for a relationship between the two moon-related variables and calling rate was apparent
but not well defined. For example, Ripley (1977) described Rouget’s rail (Rougetius rougetii) as
being ‘particularly fond of calling on moonlit nights’ but did not state how this information
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DOC Research and Development Series 365
was obtained for 12 of the 45 species (reporting rate = 27%; Table 1). However, most time-of-year
eects appeared to coincide with or were near to the breeding season, suggesting that they were
related to the reproductive status and stage. For example, Polak (2005) found that the calling
rate of water rails (R. aquaticus) peaks in April and June, around the time of egg laying, which
is consistent with the postulation that these calls are associated with mate guarding and mate
attraction (Catchpole 2003; Cramp & Simmons cited in Ręk 2015). In addition, some publications
reported multiple peaks in calling across the year (Conway & Gibbs 2011), which may have
coincided with the production of multiple clutches or females becoming available again for
mating following nest failures.
A second possibility is that monthly peaks in calling rate are byproducts of migration (i.e. a lack
of calling is due to the absence of birds rather than a change in their detectability). Seasonal
migrations have been reported for yellow rails, red-necked crakes (Rallina tricolor), white-
throated crakes (L. albigularis), grey-breasted crakes (L. exilis) and azure gallinules (Porphyrio
flavirostris) (Harvey et al. 2014; Mittermeier et al. 2013; Reynard 1974; Stiles & Levey 1988; Taylor
1998). Like calling, the timing of these migratory behaviours will also be aected by a suite of
variables – for example, the migration of red-necked crakes, white-throated crakes and grey-
breasted crakes is linked with the wet season (Stiles & Levey 1988; Taylor 1998, p. 54; Mittermeier
et al. 2013). In general, seasonal migration patterns and the factors that aect the timing of
these have not been well studied in New Zealand or other countries. Although the eect of
moon-associated variables on avian calling rates is not well defined for Rallidae species, it has
been discussed in relation to other avian species. In particular, moon-related eects are well
reported in nocturnal species (Williams 2016), with postulations tending to relate to the foraging
eciency and/or territorial activities of animals increasing on moonlit nights due to an improved
visibility (as observed for brown skua, Catharacta Antarctica, and whip-poor-wills, Caprimulgus
vociferous; Mougeot & Bretagnolle 2000; Wilson & Watts 2006).
In terms of the other variables, the literature contained inconclusive discussions on cloud
cover in relation to three species (clapper rail, king rail and watercock (Gallicrex cinerea); two
publications), temperature in relation to four species (clapper rail, American purple gallinule
(P. martinica), American coot (Fulica americana) and common moorhen; one publication),
rainfall in relation to three species (red-legged crake (R. fasciata), water rail and watercock;
three publications) and water levels in relation to two species (white-breasted waterhen and
ash-throated crake (Mustelirallus albicollis); two publications) (Table 2). Wind speed was shown
to have no eect on the calling rate of yellow rails (two publications), but it was suggested
(ambiguously) that high winds would reduce the call detectability of four species (black
rail, clapper rail, Virginia rail and water rail; four publications). In addition, Conway (2009)
recommended that the salinity content and date of last natural disturbance variable should be
recorded during standardised North American marsh bird surveys despite no prior relationship
being reported between either of these variables and calling rate and no reasons being provided
for their inclusion or postulations regarding their biological significance.
3.3 Population demographics / biological variables
Four variables relating to population demographics were reported in the literature: sex of the
bird, reproductive status/stage, migratory behaviour and population density. Reproductive
status or stage was associated with calling rate in eight species (white-breasted waterhen (Fig. 3),
black rail, clapper rail, Virginia rail, water rail, spotted crake (P. porzana), sora and spotless
crake; 13 publications) and in four additional species anecdotally (corncrake (Crex crex), yellow
rail, red-legged crake and slaty-legged crake (R. eurizonoides); five publications) (Table 3). The
relationship between calling rate and population density varied between species, with a density-
dependent relationship being detected in sora, Virginia rail, mangrove rail and clapper rail (six
publications), an anecdotal relationship being reported for Tasmanian native hen (Tribonyx
8Williams— Factors aecting the calling rates and detectability of crake and rail species
Table 3. Demographic variables reported in peer-reviewed publications for extant
Rallidae species. × = no effect, = effect detected, ? = effect ambiguous. Reporting
rates represent the percentage of species examined (i.e. out of the 45 species for
which information could be found) that had some information regarding that variable
(regardless of the trend or any ambiguity). Superscript letters indicate references (see
footnote). See Appendix 1 for scientific names.
References: a Akhtar et al. (2015); b Ripley (1977) ; c Gibbs et al. (1991); d Reynard (1974); e Mason (1950); f Conway & Gibbs
(2011); g Brackney & Bookhout (1982); h Stiles & Levey (1988); i Legare et al. (1999); j Harvey et al. (2014); k Kaufmann (1971);
l Kaufmann (1983); m Cramp & Simmons in Ręk (2015); n Ręk (2015); o Kaufmann (1988); p Robson (2015); q Mittermeier et al.
(2013); r Polak (2005); s Conway et al. (1993); t Bogner & Baldassarre (2002); u Zembal & Massey (1987); v Zembal & Massey
(1981); w Glahn (1974); x Phillipps & Phillipps (2011); y Coates & Bishop (1997).
SPECIES SEX OF BIRD REPRODUCTIVE
STATUS OR
STAGE
MIGRATORY
BEHAVIOUR
DENSITY
Azure gallinule ?j
Black rail d,f,l f,i ?b
Clapper rail b,s,t f,u,v
Common moorhen f,g xf,g
Corncrake ?b,e
Grey-breasted crake ?h?h
Inaccessible Island rail ?b
Mangrove rail t,v
Red-legged crake ?y?p,x
Red-necked crake ?q
Slaty-legged crake ?b
Sora b,f,k; ?lf,k
Spotless crake f,o
Spotted crake m,n
Tasmanian native hen ?b
Virginia rail f,k,w; ?bf,w
Water rail r
White-breasted waterhen a
Yellow rail ?ce
Number of references 517 4 8
Reporting rate 3 (7%) 12 (27%) 4 (9%) 9 (20%)
mortierii), black rail, grey-breasted crake and Inaccessible Island rail (Atlantisia rogersi; two
publications) and no apparent relationship for common moorhen (Gallinula chloropus; two
publications) (Table 3). Calling rate also appeared to vary with the sex of the calling bird in
common moorhen, black rail and red-legged crake (five publications; Table 3). Migratory
information was particularly sparse. Yellow rails are thought to migrate (1 publication), while
migration was ambigiously linked with another three species (azure gallinule, grey-breasted
crake and red-necked crake; three publications).
Results from call-based methods would be easily misinterpreted if the call rates were density
dependent, particularly where single call-rate values relate to multiple densities (Caughley,
1977), and this would be dicult to account for in an analysis without prior information on the
actual population numbers (i.e. by using some form of spatially explicit capture recapture to
distinguish between individuals; Dawson & Eord, 2009; Stevenson et al., 2015). Similarly, sex-
dependent calling rates would be dicult to measure and account for in an analysis without
prior information on sex ratios in the population. However, since few publications reported these
relationships, they should be considered as potential variables that remain to be tested.
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DOC Research and Development Series 365
Table 4. Interactive, nuisance and other variables that have been reported in peer-reviewed publications for
extant Rallidae species. × = no effect, = effect detected, ? = effect ambiguous. Reporting rates represent
the percentage of species examined (i.e. out of the 45 species for which information could be found) that had
some information regarding that variable (regardless of the trend or any ambiguity). Superscript letters indicate
references (see footnote). See Appendix 1 for scientific names.
SPECIES LOCATION OBSERVER NOISE TIME OF
YEAR/
BREEDING
STAGE *
TIME OF
DAY
TIME OF
YEAR *
LOCATION
TIME OF
YEAR *
YEAR
OBSERVER
* PLAYBACK
CALL
BROADCAST
American coot c,f; ?e
American purple gallinule c,d;?e
Austral rail z
Bare-eyed rail g
Black rail c,k,l c,k ?mc,i,j c,k c,d,e,l,n
Clapper rail c,ab c,d c,d,e,q,ab
Common moorhen c,d,e; xq
Galapagos crake o
Grey-breasted crake ?h?h
King rail ?vc,d,e,f,q
Ocellated crake p
Red-necked crake g
Slaty-legged crake xa
Sora c,u ?vc,r,s c,r,s,t c,d,e,f,w,x,y
Virginia rail c,u ae c,r c,d,ac c,r,ad c,d,e,f,r,v,w,x,ac,ad
Water rail aa
White-browed crake a
Yellow rail bbc,d; ?e
Number of references 6 2 5 6 6 2 5 22
Reporting rate 5 (11%) 1 (2%) 5 (11%) 3 (7%) 5 (11%) 1 (2%) 5 (11%) 17 (38%)
References: a Pratt et al. (1980); b Gibbs et al. (1991); c Conway & Gibbs (2011); d Conway & Nadeau (2010); e Ribic et al. (1999); f Erwin et al. (2002); g Mittermeier
et al. (2013); h Stiles & Levey (1988); i Kerlinger & Wiedner (1991); j Repking & Ohmart (1977); k Flores & Eddleman 1991 cited in Conway & Gibbs 2011; l Conway et
al. (2004); m Reynard (1974); n Spautz et al. (2005); o Franklin et al. (1979); p Lucindo et al. (2015); q Soehren et al. (2009); r Johnson & Dinsmore (1986); s Robertson
& Olsen (2014); t Kwartin (1995); u Griese et al. (1980); v Ripley (1977) ; w Lor & Malecki (2002); x Allen et al. (2004); y Glahn (1974); z Barnett et al. (2014); aa Jenkins &
Ormerod (2002); ab Zembal & Massey (1987); ac Gibbs & Melvin (1993); ad Manci & Rusch (1988); ae Kaufmann (1983).
3.4 Nuisance variables
Three nuisance variables were identified as having potentially important eects on the
detectability of crake and rail species. These included a location (site) variable, which aected
black rail, clapper rail, Virginia rail, white-browed crake (A. cinerea) and sora (six publications),
an observer variable, which aected black rail (two publications), and a background noise
variable, which aected yellow rail and Virginia rail (two publications), as well as grey-breasted
crake, black rail and sora, albeit anecdotally (three publications) (Table 4).
3.5 Interactive variables
Four pairs of interactive variables were reported, three of which involved the time of year (five
species, 12 publications; Table 4). These included an interactive eect between time of year
(or breeding stage) and calling at dierent times of the day, which was found for three species
(yellow rail, sora and Virginia rail; four publications) and suggested anecdotally for one species
(king rail; one publication), as well as interactive eects between time of year and both location
(black rail and Virginia rail; five publications) and year (black rail, sora and Virginia rail; six
publications). However, since breeding status and stage will always vary among locations and
10 Williams— Factors aecting the calling rates and detectability of crake and rail species
years and are not directly measured in most studies,2 it is likely that these three interactions are
the product of the same factor, i.e. that the daily calling-rate patterns are defined by the breeding
status/stage for these species.
The fourth interactive variable involved an observer eect when playback was used with clapper
rails (two publications; Table 4). However, as playback was the principle focus of these studies,
no independent passive listening data were available for comparison, creating the possibility that
this eect was simply a traditional ‘observer eect’ rather than being dependent on the detection
method that was used (i.e. passive or playback). Given the paucity of studies that have modelled
the factors that influence calling rates, a wide range of interactions among variables is possible.
Therefore, an open mind will be required throughout analysis.
4. Implications for monitoring New Zealand
crakes and rails
This review shows that few conclusive studies have been undertaken to identify and quantify
the factors that aect the calling rates (and therefore detectability) of crake and rail species.
Furthermore, the results that have been obtained by the limited number of studies that do exist
have tended to be ambiguous because several factors will aect the calling rate concurrently
and may interact, confounding our ability to separate these analytically. For example, Nadeau
et al. (2008) found that the calling rate of common moorhens was higher in the morning than
in the evening, but also noted that the air temperature was significantly higher in the evening.
Furthermore, the same authors also reported that clapper rails had significantly higher calling
rates in the morning than at night, but noted cloud cover and wind speed were significantly
dierent between the two time periods (both higher in the morning). Therefore, unless these
variables are controlled for through modelling or the sample sizes are particularly large, it will not
be possible to determine the importance of these eects and quantify their eect sizes (Williams
2016) – a notion that is supported by the high ambiguity that was observed for environmental
eects (which are harder to control for) compared with temporal and interactive eects.
It is speculated that most Rallidae calls function in mate guarding and attraction (Catchpole
2003; Cramp & Simmons cited in Ręk 2015), making it likely that calling rates will fluctuate with
reproductive or behavioural factors, as well as other unmeasurable factors that aect breeding
status and stage, such as hormone levels (i.e. Ręk 2015) . Therefore, where possible, it would
be useful to obtain data regarding the time of year and breeding status/stage to allow these to
be accounted for during analysis. However, information on the reproductive status and stage
is generally more dicult to obtain than calling rates due to the cryptic nature of the majority
of Rallidae, so these factors will have lower reporting rates and be less well understood than
environmental and temporal factors. Consequently, where these data are unavailable, time of
month should be modelled for New Zealand Rallidae, while keeping in mind the potential for a
causal relationship with breeding status and stage.
Options for accounting for variables in monitoring programmes include undertaking repeat
counts under standardised conditions and recording relevant variables so that their eects can
be corrected for during later analysis. Future research should identify which of the variables
identified in this review influence the calling rates and detection probabilities of New Zealand
crakes and rails to develop monitoring methods that are most suited to our wetlands. In
2 The reason for this lack of information regarding breeding status and stage varies between publications but is generally due to
diculties in measuring this covariate or because this was out of scope for the study.
11
DOC Research and Development Series 365
Table 5. Explanatory variables for consideration when modelling the calling rates of New Zealand crake and rail
species.
VARIABLE HYPOTHESES/RELATIONSHIPS TO CONSIDER RELATIONSHIP TYPE
Time of year TOY • Calling peaks during a particular month 1. Categorical (fixed)
• Calling peaks during the reproductive season 2. Categorical (fixed)
Time of day TD • Calling rate increases in relation to sunrise/sunset times 1. Polynomial/categorical (fixed)
• Calling peaks during a certain time period, e.g. morning, evening, night 2. Binomial/categorical (fixed)
Water level WL • Calling rate increases with flooding events because nests have failed 1. Binomial/linear (fixed)
• Calling rate decreases with flooding events because birds have moved 2. Binomial/linear (fixed)
Rainfall Rn • Calling rate is not related to rainfall 1. Linear (fixed)
Cloud cover Cld • Calling rate is not related to cloud cover provided moon visibility is also
included in the model
1. Linear (fixed)
Moon phase MPh • Calling rate increases as the moon approaches the full moon phase 1. Linear (fixed)
Moon visibility MV • Calling rate increases when the moon is visible (no cloud) and has risen 1. Linear (fixed)
Wind speed WS • Calling rate decreases with increased wind speed 1. Linear (fixed)
Temperature T• Calling rate is not related to temperature provided time of day is also included
in the model
1. Linear (fixed)
Background noise Ns • Calling rate increases as background noise decreases because calls register
on sound files better
1. Linear (fixed)
• Calling rate increases as background noise increases because birds give more
alarm calls
2. Binomial/linear (fixed)
Year Yr • Calling rate is not related to year because it is predictable and stable across
years
1. Linear (fixed)
Recorder Rec • Calling rate does not vary between recording devices (our equivalent of an
observer effect)
1. Random
reality, our ability to determine the optimum time for detecting Rallidae calls in New Zealand
will depend on the strength of these causal relationships and our ability to represent them
meaningfully. This will only be possible using modelling techniques and may require the
inclusion of several interactive eects. As such, Table 5 outlines the hypotheses and relationships
that are recommended for consideration when modelling the calling rates of Rallidae species in
New Zealand based on the findings of this review.
5. Acknowledgements
Thanks to Hugh Robertson and Colin O’Donnell for improving earlier drafts of this manuscript.
Funding was provided by the Arawai Kākāriki Wetland Restoration Fund.
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Appendix 1
Scientific name and IUCN classification of the species
examined
The following table lists the scientific names and the International Union of Conservation
of Nature (IUCN) Red List classifications of the 137 Rallidae species that were examined to
determine factors aecting calling rate. Note that the taxonomy of many Rallidae species is
currently under review, which are reported as ‘Not recognised by IUCN’.
COMMON NAME SCIENTIFIC NAME CLASSIFICATION
African crake Crex egregia Least Concern
African rail Rallus caerulescens Least Concern
African swamphen Porphyrio madagascariensis Not recognised by IUCN
Allen’s gallinule / lesser gallinule Porphyrio alleni (formerly Porphyrula alleni)Least Concern
American coot Fulica Americana Least Concern
American purple gallinule Porphyrio martinicus Least Concern
Andaman crake Rallina canningi Least Concern
Andean coot Fulica ardesiaca Least Concern
Ash-throated crake Porzana albicollis Least Concern
Auckland rail Lewinia muelleri Vulnerable
Austral rail Rallus antarcticus Vulnerable
Australasian swamphen Porphyrio melanotus Not recognised by IUCN
Australian spotted crake Porzana fluminea Least Concern
Azure gallinule Porphyrio flavirostris Least Concern
Band-bellied crake Zapornia paykullii Near Threatened
Bare-eyed rail Gymnocrex plumbeiventris Least Concern
Barred rail Hypotaenidia torquata Least Concern
Black crake Zapornia flavirostra Least Concern
Black rail Laterallus jamaicensis Near Threatened
Black-backed swamphen Porphyrio indicus Not recognised by IUCN
Black-banded crake Porzana fasciata Least Concern
Blackish rail Pardirallus nigricans Least Concern
Black-tailed crake Zapornia bicolor Least Concern
Black-tailed native-hen Tribonyx ventralis Least Concern
Blue-faced rail / bald-faced rail Gymnocrex rosenbergii Vulnerable
Bogotá rail Rallus semiplumbeus Endangered
Brown crake Zapornia akool Least Concern
Brown wood-rail Aramides wolfi Vulnerable
Brown-banded rail Lewinia mirifica Data Deficient
Buff-banded rail Hypotaenidia philippensis Least Concern
Calayan rail Gallirallus calayanensis Vulnerable
Chestnut forest-rail Rallicula rubra Least Concern
Chestnut rail Eulabeornis castaneoventris Least Concern
Chestnut-headed crake Rufirallus castaneiceps Least Concern
Clapper rail Rallus crepitans Least Concern
Colombian crake Neocrex colombiana Data Deficient
Common gallinule Gallinula galeata Not recognised by IUCN
Common moorhen Gallinula chloropus Least Concern
Corncrake Crex crex Least Concern
Dot-winged crake Porzana spiloptera Vulnerable
Dusky moorhen Gallinula tenebrosa Least Concern
Continued on next page
16 Williams— Factors aecting the calling rates and detectability of crake and rail species
COMMON NAME SCIENTIFIC NAME CLASSIFICATION
Eastern water rail Rallus indicus Least Concern
Eurasian coot / common coot Fulica atra Least Concern
Forbes’s forest-rail Rallicula forbesi Least Concern
Galapagos rail Laterallus spilonota Vulnerable
Giant coot Fulica gigantea Least Concern
Giant wood-rail Aramides ypecaha Least Concern
Gough moorhen Gallinula comeri Vulnerable
Grey-breasted crake Laterallus exilis Least Concern
Grey-headed swamphen Porphyrio poliocephalus Not recognised by IUCN
Grey-necked wood-rail Aramides cajaneus Least Concern
Grey-throated rail Canirallus oculeus Least Concern
Guadalcanal rail Hypotaenidia woodfordi Near Threatened
Guam rail Hypotaenidia owstoniExtinct in the Wild
Hawaiian coot / ‘Alae ke‘oke‘o Fulica alai Vulnerable
Henderson crake Zapornia atra Vulnerable
Horned coot Fulica cornuta Near Threatened
Inaccessible Island rail Atlantisia rogersi Vulnerable
Invisible rail / Wallace’s rail / drummer rail Habroptila wallacii Vulnerable
Isabelline bush-hen Amaurornis isabellina Least Concern
Junin rail Laterallus tuerosi Endangered
King rail Rallus elegans Near Threatened
Lesser moorhen Gallinula angulate Least Concern
Lewin’s rail Lewinia pectoralis Least Concern
Little crake Zapornia parva Least Concern
Little wood-rail Aramides mangle Least Concern
Lord Howe woodhen Hypotaenidia sylvestris Endangered
Madagascar rail Rallus madagascariensis Vulnerable
Madagascar wood-rail Mentocrex kioloides Least Concern
Mangrove rail Rallus longirostris Least Concern
Marsh crake (Baillon’s crake) Porzana pusilla / Zapornia pusilla Least Concern
Mayr’s forest-rail Ralicula mayri Least Concern
Mexican rail Rallus tenuirostris Near Threatened
New Britain rail / pink-legged rail Hypotaenidia insignis Near Threatened
New Caledonian rail Gallirallus lafresnayanus Critically Endangered
New Guinea flightless rail / Papuan
flightless rail
Megacrex inepta Least Concern
Nkulengu rail Himantornis haematopus Least Concern
Ocellated crake Micropygia schomburgkii Least Concern
Okinawa rail Hypotaenidia okinawae Endangered
Paint-billed crake Neocrex erythrops Least Concern
Pale-vented bush-hen / rufous-tailed
bush-hen / rufous-tailed waterhen
Amaurornis moluccana Least Concern
Philippine bush-hen Amaurornis olivacea Least Concern
Philippine swamphen Porphyrio pulverulentus Not recognised by IUCN
Plain-flanked rail Rallus wetmorei Endangered
Plumbeous rail Pardirallus sanguinolentus Least Concern
Purple swamphen Porphyrio porphyrio Least Concern
Red-and-white crake Laterallus leucopyrrhus Least Concern
Red-fronted coot Fulica rufifrons Least Concern
Red-gartered coot Fulica armillata Least Concern
Red-knobbed coot Fulica cristata Least Concern
Appendix 1 continued
Continued on next page
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COMMON NAME SCIENTIFIC NAME CLASSIFICATION
Red-legged crake Rallina fasciata Least Concern
Red-necked crake Rallina tricolor Least Concern
Red-winged wood-rail Aramides calopterus Least Concern
Ridgway’s rail Rallus obsoletus Near Threatened
Rouget’s rail Rougetius rougetii Near Threatened
Roviana rail Hypotaenidia rovianae Near Threatened
Ruddy crake Laterallus ruber Least Concern
Ruddy-breasted crake Zapornia fusca Least Concern
Rufous-faced crake Laterallus xenopterus Vulnerable
Rufous-necked wood-rail Aramides axillaris Least Concern
Rufous-sided crake Laterallus melanophaius Least Concern
Russet-crowned crake Rufirallus viridis Least Concern
Rusty-flanked crake Laterallus levraudiVulnerable
Sakalava rail Zapornia olivieri Endangered
Sharpe’s rail Gallirallus sharpei Not recognised by IUCN
Slaty-breasted rail Lewinia striata Least Concern
Slaty-breasted wood-rail Aramides saracura Least Concern
Slaty-legged crake Rallina eurizonoides Least Concern
Snoring rail / Celebes rail / Platen’s rail Aramidopsis plateni Vulnerable
Sora Porzana carolina Least Concern
Speckled crake Coturnicops notatus Least Concern
Spot-flanked gallinule Gallinula melanops Least Concern
Spotless crake Zapornia tabuensis/ Porzana tabuensis Critically Endangered
Spotted crake Porzana porzana Least Concern
Spotted rail Pardirallus maculatus Least Concern
Striped crake Amaurornis marginalis Least Concern
Swinhoe’s rail Coturnicops exquisitus Vulnerable
Takahē / South Island takahē Porphyrio hochstetteri Endangered
Talaud bush-hen Amaurornis magnirostris Vulnerable
Talaud rail Gymnocrex talaudensis Endangered
Tasmanian native-hen Tribonyx mortierii Least Concern
Tsingy wood-rail Mentocrex beankaensis Near Threatened
Uniform crake Amaurolimnas concolor Least Concern
Virginia rail Rallus limicola Least Concern
Watercock Gallicrex cinereal Least Concern
Weka Gallirallus australis Vulnerable
Western water rail Rallus aquaticus Least Concern
White-breasted waterhen Amaurornis phoenicurus Least Concern
White-browed crake Amaurornis cinerea Least Concern
White-striped forest-rail Rallicula leucospila Near Threatened
White-throated crake Laterallus albigularis Least Concern
White-throated rail / Cuvier’s rail Dryolimnas cuvieri Least Concern
White-winged coot Fulica leucoptera Least Concern
Yellow rail Coturnicops noveboracensis Least Concern
Yellow-breasted crake Hepalocrex flaviventer Least Concern
Zapata rail Cyanolimnas cerverai Critically Endangered
Appendix 1 continued
