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The Condor 104:899–902
q The Cooper Ornithological Society 2002
NEST MONITORING AND PREDATOR VISITATION AT NESTS OF BANDED DOTTERELS
RACHEL J. KEEDWELL1,3 AND MARK D. SANDERS2
1Ecology Group, Institute of Natural Resources, Massey University, Private Bag 11-222,
Palmerston North, New Zealand
2Department of Conservation, Private Bag, Twizel, New Zealand
Abstract.
We used videocameras to monitor 39
Key words: Banded Dotterel, Charadrius bicinctus
,
nests of the Banded Dotterel (
Charadrius bicinctus), a
investigator disturbance, nest monitoring, predation,
ground-nesting plover endemic to New Zealand that
videocameras.
suffers from predation by introduced mammals. To test
whether monitoring nests increased the chances of
Control de Nidos y Visita de Depredadores a
nests being visited by predators, 22 of the video-mon-
Nidos de
Charadrius bicinctus
itored nests were approached on foot daily to simulate
conventional monitoring and 17 unapproached nests
Resumen.
Usamos ca´maras de video para controlar
were monitored using videocameras only. The propor-
39 nidos de
Charadrius bicinctus, un ave ende´mica de
tions of approached nests (46%) and unapproached
Nueva Zelandia que anida en el suelo y es depredada
nests (41%) that were visited by predators did not dif-
por mamı´feros introducidos. Diariamente nos acerca-
fer significantly, nor was there any evidence that pred-
mos a pie a 22 de los nidos controlados con ca´maras
ators used human scent trails to locate nests. This study
para simular el modo convencional de seguimiento, y
provides some evidence that monitoring Banded Dot-
controlamos 17 nidos usando so´lo las ca´maras y sin
terel nests by regularly checking them does not influ-
acercarnos a ellos con el fin de examinar si el control
ence their risk of predation.
convencional de nidos incrementa la probabilidad de
visita de depredadores. La proporcio´n de nidos per-
sonalmente examinados (46%) y no examinados en
persona (41%) que fueron visitados por depredadores
Manuscript received 24 July 2001; accepted 24 June
no difirio´ significativamente, y no hubo evidencia que
2002.
los depredadores usan rastros de olores humanos para
3 E-mail: [email address]
localizar los nidos. Este estudio sugiere que controlar
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regularmente los nidos de
Charadrius bicinctus no in-
tery that were hidden 30–60 m away. Nests were
fluencia su riesgo de depredacio´n.
filmed continuously until hatching or failing, and tapes
and batteries were changed daily. Full details of the
camera configuration are available in Sanders and Ma-
Monitoring nesting success of birds involves a degree
loney (2002).
of disturbance by the researcher, and this may influ-
Nests monitored with cameras were alternately as-
ence nest survival (reviewed in Go¨tmark 1992). One
signed one of two treatments: ‘‘approached,’’ where
effect of disturbance may be to alter predation rates,
nests were approached on foot daily from the same
and it is widely believed that mammalian predators in
direction each time (simulating traditional nest moni-
particular pose a threat to nests visited by researchers
toring); and ‘‘unapproached,’’ where nests were not
(Bart 1977, Lenington 1979, Lloyd et al. 2000). How-
approached between initial camera set-up and the end
ever, research to date has provided contradictory re-
of incubation. Approached and unapproached nests
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sults, with some studies concluding that researchers
were distributed evenly over the length of the river (10
increased predation rates (Go¨tmark et al. 1990, Esler
km) in each year. For approached nests, we used the
and Grand 1993, Sandvik and Barret 2001) and others
same direction of approach as we had when the nest
indicating that researchers either had no effect or re-
was first located.
duced predation rates (O’Grady et al. 1996, Skagen et
Videotapes were watched daily and nests were cat-
al. 1999, Lloyd et al. 2000). These results suggest that
egorized as visited or not visited by predators. The
interactions between habitat, predator species, and prey
proportions of approached and unapproached nests that
species influence the effect of researchers on nest sur-
were visited were compared using contingency table
vival. Relatively few studies have examined this effect
analyses. Data from all three years were pooled be-
outside North America and Europe (Go¨tmark 1992)
cause sample sizes were too small to test for differ-
and it is important to assess the effect of researchers
ences among years. Ten nests that hatched or failed
in all nest success studies.
within three days of the camera set-up were excluded
In the large, braided riverbed systems of the Mac-
from the data set to rule out any potential effects of
kenzie Basin, South Island, New Zealand, many re-
the initial camera set-up, and because we considered
searchers have monitored breeding success of both
that human scent trails would still be fresh at unap-
common and endangered ground-nesting bird species,
proached nests for at least this length of time.
many of which rely entirely on braided riverbeds for
To assess whether predators followed human scent
breeding (Maloney 1999), yet none have formally
trails to the nest, the direction of predator and human
measured researcher impact on nest outcome. The
approaches to the same nest were compared using the
main cause of nest failure in this environment is pre-
Rayleigh test for circular uniformity (Zar 1999). The
dation by introduced mammals such as feral cats (
Felis
direction of human approach was set at 08 and each
catus), ferrets (
Mustela furo), stoats (
M. erminea) and
predator visit was categorized into one of twelve 308
hedgehogs (
Erinaceus europaeus; Pierce 1996, Sand-
segments relative to the human approach path (08, 308,
ers and Maloney 2002).
608, etc., up to 3608).
Traditionally, assessing nest survival rates has in-
To assess whether the videocameras affected pre-
volved regular visits to active nests. Now, remotely
dation rates, we used contingency table analysis to
operated video systems are widely available and can
compare predation rates at the 39 videotaped nests
be used to monitor nests with minimal disturbance (In-
with those at 227 Banded Dotterel nests that were
nes et al. 1994, Pietz and Granfors 1996, Brown et al.
monitored by field observers in a concurrent study on
1998). We used videocameras at nests to (1) test
the Ohau River (RJK, unpubl. data). Nests were clas-
whether regularly approaching nests resulted in in-
sified as preyed upon if one or more eggs were lost to
creased visitation rates by predators; and (2) assess
predators. Human-monitored nests were visited every
whether mammalian predators used human scent trails
2–4 days until the nesting attempt ended. As with the
to locate nests. We also compared predation rates at
video-monitored nests, nests that hatched or failed
video-monitored nests and nests that were inspected
within three days of discovery were excluded from
regularly but not video-monitored, to test whether the
analysis. There were no significant differences in pre-
videocameras affected nest survival.
dation rates at video-monitored and human-monitored
METHODS
nests among years; thus data from all three years were
pooled. Percentages are reported with 95% binomial
We placed videocameras at nests of a small, common
confidence intervals.
plover, the Banded Dotterel (
Charadrius bicinctus) in
the Ohau River, South Island, New Zealand (448209S,
RESULTS
1708119E) from mid-September to the end of Decem-
ber, 1998 to 2000. We found nests by following breed-
We videotaped outcomes for 22 approached nests and
ing adults to their nests. Banded Dotterels usually lay
17 unapproached nests over the three years. Filming
three eggs in a shallow hollow in the gravel. Both
effort (mean days filming per nest 6 SE) was similar
parents share the incubation of the eggs (usually 28
at approached (15.3 6 1.3 days) and unapproached
days), average hatching success is 56% (Rebergen et
(13.8 6 1.8 days) nests.
al. 1998), and 83% of chicks leave the nest within two
We recorded predator visits to 10 approached nests
days of the last chick hatching (Sanders and Maloney
and seven unapproached nests. Two visits resulted in
2002).
the predation of newly hatched chicks and at one of
Cameras and infrared lights were placed 1–2 m from
those nests an adult was also taken. Seven visits were
nests and connected to a video recorder and 12-V bat-
nonlethal and during the remaining visits one or more
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901
TABLE 1.
Details of predator visits to video-monitored Banded Dotterel nests that were either approached
daily (approached nests) or not approached after the initial camera set-up (unapproached nests). Unless otherwise
stated, each item represents a single nest. Numbers in parentheses indicate the difference in degrees between
the approach paths of human observers and predators. No angle is given for the magpie visit because it ap-
proached from above.
Predator visits to nests
Approached nests
Unapproached nests
Year
(
n 5 22)
(
n 5 17)
1998
Cat ate 1 of 2 eggs (308)
Mouse visited nest, 5 days later cat ate
Mouse visited nest (3008)
1 of 3 eggs
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Australian Magpie ate 3 chicks
Cat visited same nest on 3 nights
1999
Cat ate eggs at 3 nests (308, 1808, 1808)
Cat ate 3 eggs
Cat ate 3 chicks and 1 adult (1208)
Hedgehog visisted nest
Hedgehog ate 3 eggs (2108)
Cat visited nest (1208)
2000
Hedgehog ate 3 eggs (2108)
Hedgehog ate 3 eggs
Australian Magpie visited nest
Australasian Harrier ate 3 eggs
Total nests visited
10
7
of the eggs were preyed upon (Table 1). The same
use olfactory cues (Lavers and Clapperton 1990, Sand-
species of predators were recorded at both approached
ers and Maloney 2002). No ferret depredations were
and unapproached nests. Listed in decreasing order of
recorded in this study, but ferrets were responsible for
visits, they included feral cats, hedgehogs, mice (
Mus
21% of 69 videotaped predations at braided-river bird
musculus), Australian Magpie (
Gymnorhina tibicen)
nests (Sanders and Maloney 2002). If ferrets do hunt
and Australasian Harrier (
Circus approximans).
by smell, there is a possibility that monitoring nests
The proportion of approached (46%, 24–68% CI)
may increase ferret predation rates. However, given
and unapproached (41%, 18–67% CI) nests visited by
that cats and hedgehogs together account for over two-
predators did not differ significantly (x2 5 0.1,
P .
thirds of depredations at nests (Sanders and Maloney
1
0.7). There was no evidence to suggest that the direc-
2002), and that there was no evidence that either of
tions of approach by visiting predators and by humans
these species used human scent trails to locate nests
were correlated (
n 5 9;
z 5 0.8,
P . 0.20; magpie
(this study); it is unlikely that nest monitoring has any
visit excluded). The proportions of video-monitored
appreciable effect on nest survival in this braided-river
(31%, 17–48% CI) and human-monitored (24%, 18–
environment.
30% CI) nests that were depredated did not differ sig-
Our comparison of predator visits to nests assumes
nificantly (x2 5 0.5,
P 5 0.46).
that videos yield an unbiased picture of what happens
1
at nests. This is difficult to test because any method of
DISCUSSION
observation potentially has an effect. Conspicuous nest
In this study, sample sizes in each year were small, a
markers, such as videocameras, may increase nest pre-
direct limitation of the number of cameras available.
dation rates (Go¨tmark 1992). The videocameras used
Although the proportions of approached and unap-
in our study were up to 40 cm high, and some of the
proached nests visited by predators were similar, a
infrared lights emitted small amounts of visible light
power analysis of the data indicated that with the given
at night; thus the cameras or lights may have provided
sample size, 0.44 was the minimum difference be-
visual cues to attract either mammals or birds to the
tween the two proportions that could have been de-
nests. However, our comparison showing no difference
tected (with a 5 0.1, b 5 0.9). Therefore, there may
in predation rates at video-monitored and human-mon-
have been a difference in visitation rates between the
itored Banded Dotterel nests suggests this is not the
two treatments that we could not detect. However, we
case. Also, behavioral observations have shown that
approached nests daily, which is more frequent than
mammalian predators approached the nests and not the
usual for nest monitoring, and the lack of a strong
camera (Sanders and Maloney 2002); and although
effect of frequent monitoring on predator visitation
avian predators such as Australasian Harriers and Aus-
rates suggests that traditional nest monitoring every 2–
tralian Magpies are abundant in the braided-river envi-
4 days is even less likely to influence nest survival.
ronment (Keedwell and Brown 2001) they were respon-
Our results also suggest that approaching nests had
sible for fewer than 3% of 69 videotaped predations
little influence on how predators located nests. Again,
(Sanders and Maloney 2002) and are therefore unlikely
sample sizes were small, but predators approached
to be using videocameras to locate nests. Video-
nests from seemingly random directions that did not
monitored and human-monitored nests of the Black-
correlate with human scent trails to nests. Observations
fronted Tern (
Sterna albostriata), a species that shares
of predator behavior have shown that cats tend to use
the habitat of the Banded Dotterel, also showed no
visual cues to locate nests (Fitzgerald 1990, Sanders
significant difference in survival between the two treat-
and Maloney 2002), whereas ferrets and hedgehogs
ments (Sanders and Maloney 2002, RJK, unpubl.
902
SHORT COMMUNICATIONS
data), which further suggests that videocameras do not
of the Resource Technology Conference, Univer-
have a detrimental effect on nest survival.
sity of Melbourne, Melbourne.
The use of videocameras helped us investigate the
KEEDWELL, R. J., AND K. P. BROWN. 2001. Relative
effects of nest monitoring because the cameras record-
abundance of mammalian predators in the upper
ed nest fates without physical nest checks. Without
Waitaki Basin, South Island, New Zealand. New
cameras, the only other method for testing researcher
Zealand Journal of Zoology 28:31–38.
effect is to alter the frequency of monitoring, because
LAVERS, R. B., AND B. K. CLAPPERTON. 1990. Ferret,
nests must be approached at some stage to determine
p. 320–330.
In C. M. King [ED.], The handbook
outcome (e.g., Nichols et al. 1984, Major 1990, Sand-
of New Zealand mammals. Oxford University
vik and Barret 2001). Videocameras also increase the
Press, Auckland, New Zealand.
amount of information available by providing data on
LENINGTON, S. 1979. Predators and blackbirds: the
whether predators use human scent trails to locate
‘‘uncertainty principle’’ in field biology. Auk 96:
Downloaded from https://academic.oup.com/condor/article-abstract/104/4/899/5151826 by guest on 12 August 2019
nests and whether nest monitoring attracts different
190–192.
species of predators.
LLOYD, P., R. M. LITTLE, AND T. M. CROWE. 2000. In-
Video-monitoring provides valuable opportunities to
vestigator effects on the nesting success of arid-
compare different methods of nest monitoring on other
zone birds. Journal of Field Ornithology 71:227–
species. Although the financial costs associated with
235.
running videocameras may be high, we believe video
MAJOR, R. E. 1990. The effect of human observers on
monitoring provides a comprehensive method for in-
the intensity of nest predation. Ibis 132:608–612.
vestigating the relationships among nest survival, nest
MALONEY, R. F. 1999. Bird populations in nine braided
monitoring, and the effects of predators.
rivers of the Upper Waitaki Basin, South Island,
New Zealand: changes after 30 years. Notornis
We thank Rory McGirr, Nikki Wells, Jo Tilson,
46:243–256.
Lana Hastie, Anita Spencer, and Gavin Udy for oper-
NICHOLS, J. D., H. F. PERCIVAL, R. A. COON, M. J.
ating the videocameras. Duncan Hedderley provided
CONROY, G. L. HENSLER, AND J. E. HINES. 1984.
statistical advice, and Murray Potter, John Innes, Ed
Observer visitation frequency and success of
Minot, Hanno Sandvik, and one anonymous reviewer
Mourning Dove nests: a field experiment. Auk
provided helpful comments on earlier drafts. This work
101:398–402.
was funded by Project River Recovery (Department of
O’GRADY, D. R., D. P. HILL, AND R. M. R. BARCLAY.
Conservation), Massey University, Miss E. L. Hellaby
1996. Nest visitation by humans does not increase
Indigenous Grasslands Research Trust, and the J. S.
predation on Chestnut-collared Longspur eggs and
Watson Conservation Trust (Royal Forest and Bird
young. Journal of Field Ornithology 67:275–280.
Protection Society).
PIERCE, R. J. 1996. Ecology and management of the
Black Stilt
Himantopus novaezelandiae. Bird
LITERATURE CITED
Conservation International 6:81–88.
PIETZ, P. J., AND D. A. GRANFORS. 1996. Identifying
BART, J. 1977. Impact of human visitations on avian
predators and fates of grassland passerine nests
nesting success. Living Bird 16:187–192.
using miniature video cameras. Journal of Wildlife
B
Management 64:71–87.
ROWN, K. P., H. MOLLER, J. INNES, AND P. JANSEN.
1998. Identifying predators at nests of small birds
REBERGEN, A., R. KEEDWELL, H. MOLLER, AND R. MA-
in a New Zealand forest. Ibis 140:274–279.
LONEY. 1998. Breeding success and predation at
E
nests of Banded Dotterel (
Charadrius bicinctus)
SLER, D., AND J. B. GRAND. 1993. Factors influencing
on braided riverbeds in the central South Island,
depredation of artificial duck nests. Journal of
New Zealand. New Zealand Journal of Ecology
Wildlife Management 57:244–248.
22:33–41.
FITZGERALD, B. M. 1990. House cat, p. 330–348.
In C.
SANDERS, M. D., AND R. F. MALONEY. 2002. Video
M. King [ED.], The handbook of New Zealand
monitoring of nesting Banded Dotterels, Black
mammals. Oxford University Press, Auckland,
Stilts, and Black-fronted Terns in braided rivers of
New Zealand.
the Upper Waitaki Basin. Biological Conservation
GO¨TMARK, F. 1992. The effects of investigator distur-
106:225–236.
bance on nesting birds. Current Ornithology 9:63–
SANDVIK, H., AND R. T. BARRET. 2001. Effect of in-
104.
vestigator disturbance on the breeding success of
GO¨TMARK, F., R. NEERGAARD, AND M. A
˚ HLUND. 1990.
Black-legged Kittiwake. Journal of Field Orni-
Predation of artificial and real Arctic Loon nests
thology 72:30–42.
in Sweden. Journal of Wildlife Management 54:
SKAGEN, S. K., T. R. STANLEY, AND M. B. DILLON.
429–432.
1999. Do mammalian nest predators follow hu-
INNES, J., B. CROOK, AND P. JANSEN. 1994. A time-lapse
man scent trails in the shortgrass prairie? Wilson
video camera system for detecting predators at
Bulletin 111:415–420.
nests of forest birds: a trial with North Island Ko-
ZAR, J. H. 1999. Biostatistical analysis. Prentice-Hall
kako, p. 439–448.
In I. Bishop [ED.], Proceedings
Inc., Upper Saddle River, NJ.
