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Are vehicles 'mobile bird hides'? A test of the hypothesis that 'cars cause less disturbance'.

Introduction

'Disturbance' is the disruption of the normal activity or physiology of wildlife, such as birds, in the proximity of an agent such as a person or vehicle (i.e. a stimulus; Weston et al. 2012). One broadly accepted metric used to describe disturbance is flight-initiation distance (FID), the distance between a stimulus and a bird when an escape response is initiated (Blumstein 2003). While a range of internal and external factors influence FID (Guay et al. 2013a, Guay et al. 2013c), the type of stimulus is a little studied but important one (Mcleod et al. 2013). For example, birds alter aspects of their responses including their FIDs when presented with different stimuli (Miller et al. 2001, Glover et al. 2011; Schlacher et al. 2013b; McLeod et al. 2013). The type of stimulus which is permitted in a given area is often under the influence of land managers (e.g. Antos et al. 2007), and given that disturbance is regarded as a conservation problem in some circumstances (e.g. Schlacher et al. 2013a), understanding which stimuli are associated with which responses will aid the management of disturbance (Weston and Elgar 2005, 2007, Weston et al. 2012). Theoretically, managers could permit only certain stimuli, or prescribe stimulus-specific buffer zones to minimise disturbance (Weston et al. 2009; Weston et al. 2012; Mcleod et al. 2013). Currently, the vast majority of avian FIDs available worldwide are elicited by single walkers, thus there is a dearth of available information on other, common, stimuli (Mcleod et al. 2013).

One commonly held but little tested belief is the somewhat counter-intuitive idea that birds can be approached more closely in vehicles (henceforth 'cars') than on foot i.e. the 'cars cause less disturbance' hypothesis. Many birdwatchers and photographers use cars to approach birds because they believe this allows them to approach the birds more closely than would otherwise be possible on foot (authors, pers. obs.). However, this hypothesis has only rarely been tested, and the available results vary between species, with cars evoking shorter, similar, and longer FIDs compared with single walkers (reviewed in Mcleod et al. 2013). This study aims to test whether FIDs evoked by vehicles are shorter than those evoked by a single walker on foot by examining a greater taxonomic breadth of comparisons, and by carefully conducting experimental 'approaches' to birds.

Methods

Fieldwork was conducted at the Western Treatment Plant (WTP), Werribee, near Melbourne, Victoria (38[degrees] 01'S, 144[degrees] 34'E). Access to the plant is restricted; visitors are required to obtain a permit and register each visit. The common birdwatching areas of the WTP comprise various ponds and lagoons and the coastline, all of which are easily accessible via car or foot from the roads and paths that run throughout the plant, usually between every pond. The waterbirds at the WTP are thus exposed to some human activity, by cars and humans on foot, which is less than that evident in unrestricted areas such as urban parks (Glover et al. 2011).

Measuring Flight-Initiation Distances

Fieldwork to ok place between January 2011 and January 2012. All fieldwork was conducted between 0730 and 2100 hours, and as is customary and practical, only when it was not raining and in no stronger than moderate winds. We presented two types of stimuli to waterbirds within the WTP: single walker (1.4 m/s) and car (2.8 m/s). A stimulus type was randomly selected for each fieldwork day. For each stimulus type, we recorded FID rather than Alert Distance (AD) as it is a more reliable measure of response when multiple observers collect data (Guay et al. 2013b). FID was assessed by moving towards the focal bird at a constant pace. While approach speeds can influence FIDs (Glover et al. 2011) we used approach speeds which were typical of the stimuli being tested; our aim was to mimic realistic behaviour of each stimulus type. During the approach the observer/s were silent and made no sudden body movements. The distance at which we started an approach was recorded as the Starting Distance, and was maximised i.e. we used the longest Starting Distance possible (Blumstein 2003). The distance at which the bird walked, swam, dived, or flew away in response to the approach was recorded as the FID. Approaches were included only if the bird's response was determined to occur as a result of the approach. When a flock was approached, the FID was taken from the point at which the first individual showed a response to the approach. An approach was abandoned if it was unclear whether the bird was responding to the observer or to another potential stimulus, such as a bird of prey. Depending on the target bird's original location, we approached either directly or tangentially. All distances were measured using a laser rangefinder.

For all walking approaches the observers wore standard clothes (dark pants and a dark long-sleeved top). Different vehicles (from small hatchback to 4WD twin cab) were used for car approaches. All approaches were conducted on non-breeding adult waterbirds and only single-species flocks were approached. We attempted to avoid resampling individuals by closely monitoring where birds flushed to after an approach, before moving on to the next site.

Statistical analysis

For tangential approaches, FID was calculated as the Euclidian distance between the observer and the subject at the time escape behaviour was initiated by taking into account the bypass distance, the minimum distance between the focal bird and the path of the observer (Cooper 1997). Data for both approach types were pooled for further analysis.

We restricted our statistical analyses to 15 species for which we obtained at least five FID estimates per stimulus. We used a General Linear Model (GLM) to investigate the effect of species, stimulus type and their interaction. Starting Distance, which influences FID in birds (Blumstein 2003), varied between species ([F.sub.38,595] = 5.13, P < 0.001) but not between stimuli ([F.sub.1,595] = 2.42, P = 0.120). We controlled for the difference in Starting Distance between species by including it in our models. We further used GLMs to compare responses between stimuli for all 15 species individually. All distances were [Log.sub.10] transformed prior to analyses. Summary statistics are presented as mean [+ or -] standard errors.

Results

We collected data for 657 approaches from 38 species (car, n=269; walker, n=388; Appendix 1). Results of the GLM for the 15 species for which we had five or more approaches for each stimulus (11 to 85 FIDs per species; car, 66.3 [+ or -] 2.6 m, n = 246; walker, 74.9 [+ or -] 2.3 m, n = 311) (adjusted [R.sup.2] = 0.57) revealed significant effects of Starting Distance (logged; [F.sub.1,526] = 333.68, P < 0.001), stimulus (car vs. walker; [F.sub.1,526] = 53.36, p < 0.001), and species ([F.sub.14,526] = 6.27, p < 0.001); the interaction between species and stimulus was not significant ([F.sub.14,526] = 1.57, P = 0.084) but was associated with high power (0.87). Within-species GLMs (Table 1) revealed that in every case cars had shorter FIDs compared with walkers. Eight of these fifteen comparisons were significantly different with the remaining seven having low statistical power.

Discussion

Few general principles are available to help explain FID in regard to environmental or internal factors (Weston et al. 2012), and here we have shown that the 'cars cause less disturbance' hypothesis has at least broad, and possibly universal, relevance across species. From a conservation management perspective, in no case were cars associated with longer FIDs, suggesting that at the WTP cars are effective mobile hides for observing many waterbirds. Additionally, cars can carry multiple people, thus arguably reduce the number of stimuli in an area (Mcleod et al. 2013). Birds at the WTP are exposed to many cars and perhaps fewer people on foot (though workers and birdwatchers are not uncommon on foot as they move around the vicinity of their cars; authors, pers. obs.). As for any behavioural study, confirmation of these results at different sites, with different prevailing regimes of cars and walkers, would be useful. Such a study could disentangle local learning on the part of the birds from perception and innate risk judgement of birds. It is important to note that many of the species involved in this study are migratory or nomadic and move in and out of the WTP every year (Hamilton and Taylor 2004; Hamilton et al. 2004). In particular, Australian Shelducks Tadorna tadornoides come to the WTP only during summer, thus limiting the opportunity for local adaptation.

Several caveats exist regarding the implications of the finding that cars reduce FIDs. Firstly, shorter FIDs in response to cars may not be adaptive in all circumstances. Cars cause direct bird mortality throughout the world and in Australia (Taylor and Mooney 1991; Schlacher et al. 2013a), presumably because responses are inadequate, absent or initiated too late. Such mortality can influence roadside bird populations (Bujoczek et al. 2011). The vehicle we used moved at slow speeds to mimic the prevailing speed of cars at the WTP; however, high vehicle speeds require earlier flight responses for successful evasion, and faster stimuli are associated with longer FIDs (Glover et al. 2011). At least some European birds apparently adjust their FIDs in regard to prevailing speed limits for traffic, but not to car speed per se (Legagneux and Ducatez 2013). Thus, the average speed of vehicles may influence FID and there may be a speed above which FIDs exceed those associated with walkers.

Secondly, while cars may decrease FIDs among many species, they still have profound ecological effects on birds and their habitats (e.g. Reijnen and Foppen 1994) and can cause substantial levels of disturbance to birds especially when they are driving at speed and are common (e.g. Schlacher et al. 2013a; Schlacher et al. 2013b). Roads and tracks can cause a range of negative ecological effects (Forman and Alexander 1998), and the high mobility of cars means that the 'human footprint' is more expansive than for walkers alone, at least in many areas (McLeod et al. 2013). Clearly all impacts need to be considered by managers before the decision to promote a 'disturbance mediation by stimulus' strategy occurs.

The underlying mechanisms involved in birds discriminating between cars and walkers in terms of response remain unknown (see Weston et al. 2012). Each stimulus is associated with different visual and auditory cues, with cars being relatively novel evolutionarily. If size, colour and noise are used by birds to judge risk, then responses may vary with stimulus types (e.g. hybrid versus internal combustion cars), and this would be a useful subject of future study.

Appendix 1. Raw flight-initiation distance (FID) data for all 38
species studied. We report sample size (n), mean start distance (SD)
([+ or -] one standard deviation) and mean FID ([+ or -] one standard
deviation) for each stimulus separately. Blanks indicate no data were
collected. Taxa are presented in alphabetical order by common name,
and scientific names follow BirdLife (2012).

Species                                 Car

                       n    SD (m)                 FID (m)

Australasian Darter
  Anhinga
  novaehollandiae
Australasian Grebe
  Tachybaptus
  novaehollandiae      1    30.5                   17.7
Australian Pelican
  Pelecanus
  conspicillatus       4    208.1 [+ or -] 122.3   114.6 [+ or -] 51.7
Australian Shelduck
  Tadorna
  tadornoides          43   277.5 [+ or -] 154.5   106.9 [+ or -] 48.4
Australian White
  Ibis  Threskiornis
  molucca              17   142.8 [+ or -] 78.7    56.2 [+ or -] 20.3
Black Swan
  Cygnus atratus       18   147.6 [+ or -] 89.4    66.4 [+ or -] 59.4
Black-tailed
  Native-hen
  Gallinula
  ventralis
Blue Billed Duck
  Oxyura australis
Cape Barren Goose
  Cereopsis
  novaehollandiae
Cattle Egret
  Bubulcus ibis
Chestnut Teal
  Anas castanea        33   148.6 [+ or -] 71.3    65.1 [+ or -] 29.4
Dusky Moorhen
  Gallinula
  tenebrosa            1    16                     14
Eastern Great Egret
  Ardea modesta        5    121.2 [+ or -] 119.4   32.8 [+ or -] 18.5
Eurasian Coot
  Fulica atra          14   142.0 [+ or -] 74.8    74.3 [+ or -] 47.6
Glossy Ibis
  Plegadis
  falcinellus          1    114.4                  22.9
Great Cormorant
  Phalacrocorax
  carbo                2    100.8 [+ or -] 0.7     23.5 [+ or -] 8.2
Grey Teal
  Anas gracilis        2    191.5 [+ or -] 153.4   61.6 [+ or -] 9.4
Hardhead
  Aythya australis     13   129.6 [+ or -] 62.0    64.6 [+ or -] 24.0
Hoary-headed Grebe
  Poliocephalus
  poliocephalus        1    47.3                   29.9
Intermediate Egret
  Mesophoyx
  intermedia           1    210                    20
Little Black
  Cormorant
  Phalacrocorax
  sulcirostris         6    102.4 [+ or -] 66.5    38.8 [+ or -] 22.3
Little Egret
  Egretta garzetta
Little Pied
  Cormorant
  Microcarbo
  melanoleucos         19   106.6 [+ or -] 52.3    33.9 [+ or -] 14.9
Masked Lapwing
  Vanellus miles       6    189.8 [+ or -] 96.8    40.8 [+ or -] 24.2
Musk Duck
  Biziura lobata       3    101.5 [+ or -] 77.3    34.1 [+ or -] 19.1
Pacific Black Duck
  Anas superciliosa    20   159.2 [+ or -] 80.9    72.0 [+ or -] 40.2
Pied Cormorant
  Phalacrocorax
  varius               5    202.4 [+ or -] 150.8   50.0 [+ or -] 14.0
Pink-eared Duck
  Malacorhynchus
  membranaceus
Plumed Whistling
  Duck Dendrocygna
  eytoni
Purple Swamphen
  Porphyrio
  porphyria            15   89.2 [+ or -] 29.8     43.2 [+ or -] 32.2
Red-necked Avocet
  Recurvirostra
  novaehollandiae
Red-necked Stint
  Calidris
  ruficollis           1    29.3                   26.3
Royal Spoonbill
  Platalea regia       2    56.0 [+ or -] 26.4     46.0 [+ or -] 34.9
Silver Gull
  Larus
  novaehollandiae      3    87.4 [+ or -] 19.0     17.4 [+ or -] 3.2
Straw-necked Ibis
  Threskiornis
  spinicollis          22   222.6 [+ or -] 146.3   81.8 [+ or -] 38.3
White-faced Heron
  Egretta
  novaehollandiae      10   143.5 [+ or -] 84.5    63.0 [+ or -] 31.6
White-necked Heron
  Egretta
  novaehollandiae      1    116.7                  26.4
Yellow-billed
  Spoonbill Platalea
  flavipes

Species                  Walker

                       n    SD (m)

Australasian Darter
  Anhinga
  novaehollandiae      2    108.5 [+ or -] 19.0
Australasian Grebe
  Tachybaptus
  novaehollandiae      3    70.6 [+ or -] 10.9
Australian Pelican
  Pelecanus
  conspicillatus       9    212.5 [+ or -] 123.7
Australian Shelduck
  Tadorna
  tadornoides          42   219.2 [+ or -] 131.2
Australian White
  Ibis  Threskiornis
  molucca              12   93.9 [+ or -] 41.2
Black Swan
  Cygnus atratus       40   124.1 [+ or -] 97.0
Black-tailed
  Native-hen
  Gallinula
  ventralis            6    85.0 [+ or -] 40.2
Blue Billed Duck
  Oxyura australis     3    85.1 [+ or -] 54.7
Cape Barren Goose
  Cereopsis
  novaehollandiae      5    119.6 [+ or -] 58.5
Cattle Egret
  Bubulcus ibis        1    26.9
Chestnut Teal
  Anas castanea        46   149.7 [+ or -] 71.1
Dusky Moorhen
  Gallinula
  tenebrosa
Eastern Great Egret
  Ardea modesta        16   86.1 [+ or -] 51.1
Eurasian Coot
  Fulica atra          5    92.0 [+ or -] 29.2
Glossy Ibis
  Plegadis
  falcinellus          1    68
Great Cormorant
  Phalacrocorax
  carbo                6    92.2 [+ or -] 26.0
Grey Teal
  Anas gracilis        6    145.0 [+ or -] 97.4
Hardhead
  Aythya australis     18   160.3 [+ or -] 93.1
Hoary-headed Grebe
  Poliocephalus
  poliocephalus
Intermediate Egret
  Mesophoyx
  intermedia           1    27
Little Black
  Cormorant
  Phalacrocorax
  sulcirostris         5    119.1 [+ or -] 106.7
Little Egret
  Egretta garzetta     1    39
Little Pied
  Cormorant
  Microcarbo
  melanoleucos         44   97.7 [+ or -] 57.4
Masked Lapwing
  Vanellus miles       6    142.0 [+ or -] 97.8
Musk Duck
  Biziura lobata       7    107.1 [+ or -] 42.7
Pacific Black Duck
  Anas superciliosa    17   189.6 [+ or -] 89.7
Pied Cormorant
  Phalacrocorax
  varius               13   144.8 [+ or -] 113.7
Pink-eared Duck
  Malacorhynchus
  membranaceus         12   96.2 [+ or -] 60.4
Plumed Whistling
  Duck Dendrocygna
  eytoni               1    178
Purple Swamphen
  Porphyrio
  porphyria            22   90.2 [+ or -] 47.1
Red-necked Avocet
  Recurvirostra
  novaehollandiae      1    104.6
Red-necked Stint
  Calidris
  ruficollis
Royal Spoonbill
  Platalea regia       9    73.7 [+ or -] 42.9
Silver Gull
  Larus
  novaehollandiae
Straw-necked Ibis
  Threskiornis
  spinicollis          12   164.4 [+ or -] 96.1
White-faced Heron
  Egretta
  novaehollandiae      13   77.4 [+ or -] 31.4
White-necked Heron
  Egretta
  novaehollandiae      2    71.2 [+ or -] 2.5
Yellow-billed
  Spoonbill Platalea
  flavipes             1    38.4

Species                Walker

                       FID (m)

Australasian Darter
  Anhinga
  novaehollandiae      77.4 [+ or -] 0.6
Australasian Grebe
  Tachybaptus
  novaehollandiae      53.5 [+ or -] 2.2
Australian Pelican
  Pelecanus
  conspicillatus       123.9 [+ or -] 104.9
Australian Shelduck
  Tadorna
  tadornoides          122.3 [+ or -] 59.7
Australian White
  Ibis  Threskiornis
  molucca              48.6 [+ or -] 24.8
Black Swan
  Cygnus atratus       78.3 [+ or -] 51.1
Black-tailed
  Native-hen
  Gallinula
  ventralis            52.7 [+ or -] 16.8
Blue Billed Duck
  Oxyura australis     68.3 [+ or -] 36.1
Cape Barren Goose
  Cereopsis
  novaehollandiae      82.6 [+ or -] 40.3
Cattle Egret
  Bubulcus ibis        23.4
Chestnut Teal
  Anas castanea        80.1 [+ or -] 19.9
Dusky Moorhen
  Gallinula
  tenebrosa
Eastern Great Egret
  Ardea modesta        57.0 [+ or -] 29.4
Eurasian Coot
  Fulica atra          72.8 [+ or -] 30.5
Glossy Ibis
  Plegadis
  falcinellus          45
Great Cormorant
  Phalacrocorax
  carbo                74.0 [+ or -] 20.7
Grey Teal
  Anas gracilis        82.8 [+ or -] 30.8
Hardhead
  Aythya australis     87.2 [+ or -] 44.8
Hoary-headed Grebe
  Poliocephalus
  poliocephalus
Intermediate Egret
  Mesophoyx
  intermedia           13
Little Black
  Cormorant
  Phalacrocorax
  sulcirostris         57.3 [+ or -] 69.5
Little Egret
  Egretta garzetta     35
Little Pied
  Cormorant
  Microcarbo
  melanoleucos         46.1 [+ or -] 28.8
Masked Lapwing
  Vanellus miles       79.7 [+ or -] 18.0
Musk Duck
  Biziura lobata       69.9 [+ or -] 28.8
Pacific Black Duck
  Anas superciliosa    89.1 [+ or -] 31.4
Pied Cormorant
  Phalacrocorax
  varius               77.9 [+ or -] 57.9
Pink-eared Duck
  Malacorhynchus
  membranaceus         67.1 [+ or -] 27.2
Plumed Whistling
  Duck Dendrocygna
  eytoni               130
Purple Swamphen
  Porphyrio
  porphyria            57.9 [+ or -] 26.6
Red-necked Avocet
  Recurvirostra
  novaehollandiae      32.5
Red-necked Stint
  Calidris
  ruficollis
Royal Spoonbill
  Platalea regia       48.8 [+ or -] 27.9
Silver Gull
  Larus
  novaehollandiae
Straw-necked Ibis
  Threskiornis
  spinicollis          84.9 [+ or -] 40.0
White-faced Heron
  Egretta
  novaehollandiae      46.4 [+ or -] 19.6
White-necked Heron
  Egretta
  novaehollandiae      63.4 [+ or -] 7.6
Yellow-billed
  Spoonbill Platalea
  flavipes             24.7


Acknowledgments

This research was funded by Melbourne Water, a Victoria University Fellowship and a Faculty of Health Engineering and Science Collaborative Research Grant Scheme to P-J Guay. A Deakin University School of Life and Environmental Science collaborative research grant assisted with the write-up of this work. We thank Dr WK Steele for his support, advice and comments on a draft. Data were collected under Deakin University Animal Ethics Committee Permits A48/2008 and B32/2012, Victoria University Animal Ethics Committee Permit AEETH 15/10, National Parks Permit 10004656, DSE Scientific Permits Nos 10004656 and 10005536, and Western Treatment Plant Study Permit SP 08/02.

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Received 19 December 2013; accepted 5 June 2014

Patrick-Jean Guay (1,2), Emily M McLeod (1), Alice J Taysom (1), and Michael A Weston (3) ([dagger])

(1) Applied Ecology Research Group and Institute for Sustainability and Innovation, College of Engineering and Science, Victoria University--St-Albans Campus, PO Box 14428, Melbourne MC, Victoria 8001

(2) College of Health and Biomedicine, Victoria University--St-Albans Campus, PO Box 14428, Melbourne MC, Victoria, 8001

(3) Centre for Integrative Ecology, Faculty of Science, Engineering and the Built Environment, School of Life and Environmental Sciences, Deakin University, 221 Burwood Highway, Burwood, Victoria, Australia 3125

([dagger]) Corresponding author: E-mail: mweston@deakin.edu.au

Table 1. Results of within-species GLMs for each species where at
least five approaches were recorded for each stimulus. We report
degrees of freedom (d.f.), F-value, P-value and observed power
(Power). Species are presented alphabetically, by common name
(BirdLife 2012).

Species                     d.f.    F-value   P-value   Power

Australian Shelduck         1, 82   12.11     0.001     0.930
Tadorna tadornoides

Australian White Ibis       1, 26   0.53      0.475     0.108
Threskiornis molucca

Black Swan Cygnus atratus   1, 55   10.39     0.002     0.886

Chestnut Teal Anas          1, 76   14.80     <0.001    0.967
castanea

Eastern Great Egret Ardea   1, 18   17.35     0.001     0.976
modesta

Eurasian Coot Fulica atra   1, 16   2.22      0.155     0.289

Hardhead Aythya australis   1, 28   3.42      0.075     0.431

Little Black Cormorant      1, 8    0.06      0.816     0.055
Phalacrocorax
sulcirostris

Little Pied Cormorant       1, 60   6.56      0.013     0.712
Microcarbo melanoleucos

Masked Lapwing Vanellus     1, 9    10.84     0.009     0.833
miles

Pacific Black Duck Anas     1, 34   2.33      0.136     0.317
superciliosa

Pied Cormorant              1, 15   5.14      0.039     0.564
Phalacrocorax varius

Purple Swamphen Porphyrio   1, 34   8.03      0.008     0.786
porphyrio

Straw-necked Ibis           1, 31   0.83      0.369     0.143
Threskiornis spinicollis

White-faced Heron Egretta   1, 20   0.00      0.986     0.050
Novaehollandiae
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Title Annotation:Contributions
Author:Guay, Patrick-Jean; McLeod, Emily M.; Taysom, Alice J.; Weston, Michael A.
Publication:The Victorian Naturalist
Article Type:Report
Date:Aug 1, 2014
Words:3974
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