C. Zeenath 1 & V.J. Zacharias 2
1 Associate
Professor, Wildlife Biology Division, P.G. Department of Zoology, Farook College, Kozhikode, Kerala 673632, India
2Professor, Division of Biology, Northern Virginia Community College, Manassas,
VA 20109, USA.
Email: 1 zeenathc@gmail.com
Date
of publication (online): 26 December 2010
Date
of publication (print): 26 December 2010
ISSN
0974-7907 (online) | 0974-7893 (print)
Editor: C. Srinivasulu
Manuscript details:
Ms # o1819
Received 10 July 2007
Final received 01 December 2010
Finally accepted 07 December 2010
Citation: Zeenath, C. & V.J. Zacharias (2010).
Foraging behaviour and diving pattern of Little
Cormorant Phalacrocorax niger (Vieillot) (Pelecaniformes:Phalacrocoracidae) at Kallamparabackwaters, Kerala, India. Journal
of Threatened Taxa2(13): 1382-1386.
Copyright: © C. Zeenath & V.J. Zacharias 2010. Creative Commons Attribution 3.0 UnportedLicense. JoTT allows unrestricted use of this
article in any medium for non-profit purposes, reproduction and distribution by
providing adequate credit to the authors and the source of publication.
Acknowledgements: The Authors
are grateful to Dr. Jaffer Palot(Senior Scientist, Zoological Survey of India, Kozhikode) for his valuable
suggestions. We are thankful to Director, Positional Astronomy Centre, New Alipore, Kolkota, for providing
data source for tidal height.
For figures & tables -- click here
Underwater
activity of diving fowl is a fascinating field for researchers in
ornithology. Although some dives
are made during courtship or to escape from predators, most are made to capture
prey. Diving birds may be
considered as central-place foragers (Orians &
Pearson 1979; Lessels & Stephens 1983) which make repeated foraging excursions from the surface,
to which they must return to breathe.
Cormorants
are foot-propelled pursuit divers (Ashmole1971). They typically forage by
undertaking a series of dives from the water surface interspersed with brief
recovery periods or surface pauses (Cooper 1986). The duration of dives is positively related to surface
pauses or resting time (Casaux 2004). Cormorants and Shags belonging to the familyPhalacrocoracidae are well adapted to dive in shallow
waters (Wilson et al. 1992). The
diving behaviour of cormorants is
said to be influenced by environmental features (Frereet al. 2002) and it is reported that Red-legged Cormorants are able to forage
by selecting the appropriate tidal condition to minimize foraging effort (Gandini et al. 2005).
The
Little Cormorant Phalacrocorax niger is widely distributed throughout the Indian
subcontinent (Ali 2002; Kumar et al. 2005) on inland waters, and also in
brackish lagoons and tidal creeks. Understanding the foraging behaviour and
diving pattern of this expert diver would be helpful in identifying its role in
the wetland ecosystem, currently threatened by growing developmental
activities. The aim of this study
was to generate information on the foraging behaviour,
diving pattern and the relationship between diving parameters and body mass of
Little Cormorant.
Study
Area
Observations
were made at the Kallampara River (11009’25.5”N & 75051’02.0”E) near the Kadalundy Bird Sanctuary, Kozhikode District, Kerala,
India. The river is a tributary of
the Chaliyar River that joins the Arabian Sea near Beypore and it is subjected to regular tidal influx. The river attracts other wetland birds
like the Indian Pond Heron Ardeola grayii, Grey Heron Ardea cinerea, Little Egret Egretta garzetta and Cattle Egret Bubulcus ibis. Scattered patches of mangroves such as Avicennia officinalis and Excoecaria agallocha grow along the riverside that foraging birds
use as perching sites. Observations were held in a stretch of 5km of KallamparaRiver.
The
study was conducted from August 2005 to March 2006, mainly based on direct
observational methods (Altman 1974). Data were collected from 1100 to 1600 hr, covering both low tide and
high tide. We carried out focal
observations on randomly selected foraging cormorants. Observations were made from convenient
vantage points on the shore using a stopwatch and binoculars (8 x 40). Data were recorded during high tide,
the first quarter of receding tide (immediately after high tide), low tide and
the first quarter of advancing tide (immediately after low tide). Tidal height at high tide varied
between 1.28m and 1.40m and that of low tide was 0.40-0.46 m. Depth profiles of the feeding locations
were measured during different tidal conditions by physical method using a
graduated pole.
Cormorants
foraging solitarily were studied. The duration of a diving bout is taken as the time between submerging on
the first dive of a series and surfacing after the last dive. A dive cycle consists of a single dive
and a single surface pause. Diving
efficiency is defined as the ratio between mean diving time and mean recovery
period (Dewar 1924). Data
collected from a series of dives and surface pauses (rests or recovery periods)
from a number of individuals were pooled to give mean diving and surface
resting periods, bout duration, dive cycles and dive/pause ratio. A mean value of each diving variable
was determined for each diving bout, and means were pooled to calculate overall
mean for an environmental condition. Values presented are means ± S.D.
Two-way
ANOVA was used to test significance of diving patterns during different tidal
conditions. Duration of dives are
correlated with pause duration and number of dive cycles per bout.
Little
Cormorant made foraging trips to inshore waters <10m deep. Average foraging depth was 3.83m ±
0.53, 2.78m ± 0.39, 1.34m ± 0.21 and 1.08m ± 0.12 at high tide, receding tide,
low tide and advancing tide respectively.
In
this study 20 diving bouts and 506 dive cycles were recorded (Table 1). Diving parameters showed variations at
different tidal conditions. Under water time during each dive cycle varied
between 66-75 %. Body weight of
Little Cormorant was 444.67 ± 38.59 g (n = 3).
Little
Cormorants made foraging trips to inshore water <10m deep near the bank
within a small feeding range (<1km). They followed a specific foraging pattern, which consists of perching
near the inshore water prior to the beginning of the dive. After settling on the perch, the bird
dropped into water and started diving. The first dive was followed by a short recovery period (surface pause)
and then continued a series of alternative dives and surface pauses for a specific
period (bout duration).
During
different tidal conditions, surface pause duration increased with increasing
dive duration (Fig. 1). It was
found that duration of dive decreased with increase in the number of dive
cycles per bout (Fig. 2). Duration
of dives is positively correlated with pause duration (R = 0.936, p < 0.05),
but negatively correlated to the number of dive cycles per bout (R = -0.610, p
< 0.05).
Dive
duration increased with height of the tide (diving depth). During high tide and
receding tide it almost doubled (Fig. 4; F12,486 =
2.14, p < 0.01). In the Whisker
plot maximum diving efficiency is plotted against low tide (Fig. 5) and there
is a negative correlation between tidal height (diving depth) and diving
efficiency (Fig. 6; F12,486 = 2.90, p <
0.001).
The
diving pattern during various tidal conditions shows significant differences (F3,486 = 67.61, p < 0.05). The bouts (n = 20) during different tidal conditions in
terms of dive duration, pause duration, dive cycles, dive % frequency per hour
and dive/pause ratio are also very much significant (F12,486 = 2.90, p < 0.001). Diving depth during different tidal conditions greatly influence the
diving parameters. When the bouts
are considered independently they are not significant (p > 0.05).
Discussion
A
positive relation between dive duration and subsequent recovery time was
observed in Little Cormorant as in other cormorant species (Cooper 1986; Croxall et al. 1991; Casaux2004), but negatively correlated to the number of dive cycles per bout as in
Antarctic Shag Phalacrocorax bransfieldensis (Casaux2004).
When
we consider the mean values for all the tidal conditions (Table 2), it is clear
that dives (10.46 ± 4.86 sec) and surface pauses (4.48 ± 2.52 sec) are
relatively short for Little Cormorant. It performed relatively shorter diving times and surface pauses than
other diving birds like Red-legged Cormorants Phalacrocorax gaimardi (Frere et al.,
2002), Rock Shag Phalacrocorax magellanicus (Quintana, 1999), and Imperial Shag Phalacrocorax atriceps (Croxall et al.,
1991). The difference in diving
parameters could reflect variation in diving depth which may be correlated with
body mass. Among the four species compared in this study the Little Cormorant
has the lowest body mass of 444.67 ± 38.59 g (n = 3), which comes within the
range as referred by Ali & Ripley (2001). According to Cooper (1986) there exists a relationship
between body mass and diving parameters among the family Phalacrocoracidae. As predicted by
Cooper dive duration increased with increase of body mass (Fig. 3). But contrary to Cooper’s prediction,
the diving efficiency of the Little Cormorant is not as low compared to its
body mass (Table 2).
The
underwater time (66-75 %) observed for Little Cormorant for each dive cycle is
almost equivalent to that of Red-legged Cormorant, Rock Shag, and Imperial
Shag, but it had shorter dive duration. Little Cormorant is an efficient diver in terms of the proportion of
time spent under water per diving cycle as has been described for Red-legged
Cormorant (Frere et al. 2002). During low tide and advancing tide the
time spent under water increased with decreased diving depth and utilizing the
prey availability to the maximum with increased diving efficiency. This shows that in spite of
physiological constraints, the bird was not exhausted due to its increased
underwater time.
Diving
birds may use different foraging tactics to exploit prey in the offshore and
inshore waters (Gremillet et al. 1998; Tremblay &Cherel 2000). In this study mean dive duration and mean recovery time between dives
were linked to the height of the tide (diving depth) as described for
Red-legged Cormorant (Frere et al. 2002). For longer dives the corresponding rest
periods increased and dive/ pause ratio (diving efficiency) decreased as
proposed by Stonehouse (1967) at high tide and
receding tide. During this
condition water depth and volume may increase and prey density fall. Little Cormorants spent more time
searching for prey and foraging efficiency decreased at increased diving depth.
Little
Cormorants foraging in shallow water during low tide and advancing tide might
have fed on fishes shoaling close to the surface as in Japanese Cormorant Phalacrocorax filamentosus (Watanukiet al. 2004). Fishes brought in
during high tide may gather during low tide and density increases. These fish groups could be easily
detected and foraged with increased efficiency within short dive duration in
shallow water. Little Cormorants
foraged successfully in shallow water with increased diving efficiency,
reducing diving cost and energy as has been noticed in other studies on
cormorants (Wanless et al. 1993).
As
in Red-legged Cormorants (Frere et al. 2002; Gandini et al. 2005) the foraging behaviourand diving pattern of Little Cormorant was strongly influenced by many
environmental characteristics of the habitat. Our results also suggest that the foraging behaviour of Little Cormorant is influenced by
environmental factors such as the height of the tide and diving depth. Low tide and advancing tide seems to be
the optimal condition for Little Cormorant to acquire food faster and reduce
diving cost. Its preference
for shallow water is definitely correlated to its body mass
which is reflected in the short dive duration. But the diving efficiency seems to be an indicator of the
foraging condition which can be modified according to
prey availability. Increase in the
prey availability might have enhanced the diving efficiency of Little Cormorant
during low tide and advancing tide.
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