Breeding Season of Waterbird in Tanjung Rejo, North Sumatera

Indonesia

Erni Jumilawaty, Masitta Tanjung

and Ayu Anggelicha

Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Sumatera Utara, Medan, Indonesia

Keywords: Ardea, Breeding Season, Egretta, Indonesia, North Sumatra, Waterbirds.

Abstract: Breeding season is one of the natural events occurring annually with objectives on maintaning the

population and producing the offsprings. Waterbirds require various conditions to enter the breeding season

including the sites and time of breeding. Selection of breeding sites will determine the success of breeding

waterbirds. Breeding season study was conducted using direct observation methods from August to June

during 2016-2018. This study aims to determine the breeding cycle and life cycle of waterbirds in Tanjung

Rejo district, Deli Serdang regency, North Sumatra, Indonesia. Based on the research results, the breeding

season of waterbirds in Tanjung Rejo occurs twice in a year. This breeding season of water birds occurs

simultaneously in September until December, and February-June for four identified species namely: Egretta

alba, E garzetta, Bubulcus ibis and Phalacocorax sulcirostris. As for Ardea cinerea and Nycticorax

nycticorax, breeding season occurs in August-November and January-May. The clutch size of each bird

ranges from 2 to 4 eggs. The spawning interval for each species is between 1 and 4 days, while the

spawning sequence takes place from 1 to 4 days. Incubation period ranges from 25 to 30 days. The success

of waterbird breeding is determined by both climate and food factors.

1 INTRODUCTION

Breeding season is a seasonal timing to produce new

offsprings which employ several strategies to

increase the success during the breeding season

(Martin, 1995; Perrins, 1996). Breeding is a natural

event which occurs every year by all organisms,

including water birds. The breeding season of water

birds in tropical climates may occur throughout the

year depending on the availability of resources such

as food, nesting locations and nest materials.

Waterbirds in Indonesia enter the breeding

season together with the beginning of rainy season

in each year (Mardiastuti, 1993). The duration of

breeding season for each waterbird may vary from

the starting time of the breeding season until raising

period of their. (Perrins and Birkhead, 1983). There

are two important factors which determine the

reproductive success of waterbirds, namely:

breeding time and reproductive capacity (clucth-

size) (Perrins and Birkhead, 1983; Harriman et al.,

2017). The latter factor will also affect the size of

the population and its sustainability in the future.

Some reproduction patterns include: habitat, nesting

behavior, the breeding time, number of eggs per

nest, and breeding success (Fernandez and

Reboreda, 2008; Harriman et al., 2017).

Tanjung Rejo is a habitat of waterbirds,

commonly utilized for breeding by six species of

waterbirds, within the genera of Ardea, Egretta,

Phalacrocorax, Nycticorax and Bubulcus ibis). The

mating pairs may exceed 2500 pairs of waterbirds.

Every year this location is chosen by the resident

waterbirds as a breeding site due to isolated and

protected from predator and human interference

(Jumilawaty and Aththorick, 2016). It is interesting

to learn especially to find out how the species of

waterbirds in this location determine the breeding

season and strategies for successful breeding.

2 MATERIALS AND METHOD

2.1 Breeding Season and Clutch Size

Determination of breeding season time is based on

the Julian calendar in which the date of January 1 is

equivalent to the 1

day and December 31 is

equivalent to the 365

day in a year. Observations

382

Jumilawaty, E., Tanjung, M. and Anggeliccha, A.

Breeding Season of Waterbird in Tanjung Rejo, Deli Serdang Regency, Nor th Sumatra, Indonesia.

DOI: 10.5220/0010199100002775

In Proceedings of the 1st International MIPAnet Conference on Science and Mathematics (IMC-SciMath 2019), pages 382-386

ISBN: 978-989-758-556-2

were made by directly every two days by observing

the color change of feathers on waterbirds until the

chicks are able to fly and leave the nest. The number

of nests observed was 50 nests and the number of

eggs observed was 3 eggs per nest. The beginning of

the breeding season is determined based on the time

of laying eggs for the first time by the species until

no more eggs were laid.

2.2 Hatchling Development

Breeding observations were observed directly for

every 2 days. The observations were carried out on

the nest of grey heron (Ardea cinerea) to determine

whether the number of hatched eggs. The distance of

laying eggs, hatching distance and number of chicks

were measured numetrically. The number of

surviving chicks were counted and expressed in

percentage.

3 RESULTS AND DISCUSSION

3.1 Breeding Season

Breeding season for waterbirds in three consecutive

years from 2016 to 2018, occurred throughout the

year and is closely related to food availability,

especially fish and insects (Jumilawaty and

Aththorick, 2016; Jumilawaty and Andriayani,

2019). The breeding season for water birds in

Tanjung Rejo occurred twice a year, season 1 from

August to December and season 2 from February to

June (Table 1).

Breeding season began with the physical changes

of waterbirds until the chicks learned to fly. In this

study, one breeding season occurred 3 to 4 months

depending on the waterbird species. Physical

changes can be observed in the form of discoloration

of the feathers on the beak and legs and body

feathers. The difference in the start of the breeding

season among species is a strategy to avoid

competition in food availability.

Table 1: Breeding season of waterbirds in Tanjung Rejo, Deli Serdang Regency, North Sumatra.

In Table 1 It can be seen that there are three

variations in the strategy of waterbirds in the

breeding season. Ardea cinerea started the breeding

season earlier than other waterbirds every year,

followed by Egretta alba and Phalacrocorax

sulcirostris then followed by Egretta garzetta and

Bubulcus ibis. Interestingly enough in 2016-2017,

Nycticorax nycticorax was not found to nest and

breed in this location together with other waterbirds

but in 2018, its nest was found at the same time with

A. cinerea neir their nest trees. Selection of varying

breeding time by waterbirds found in Tanjung Rejo

aims to enhance the success rate of breeding whilst

to avoid competition, leading to survivability of its

offsprings in the future.

The large body size of grey heron (Ardea

cinerea) require it to supply more food resources

and nest material than other waterbirds species

which explain the early start of their breeding

season. Whereas, the great egret (Egretta alba), little

black cormorant (Phalacrocorax sulcirostris) little

egret (E. garzetta), and cattle egret (Bubulcus ibis)

chose to breed simultaneously to avoid predators

(Jumilawaty and Andriayani, 2019).

Different with black-crowned night heron

(Nycticorax nycticorax), in 2016-2017, they

preferred a further breeding site than any other

waterbird species. This is assumed due to

incompetitiveness by the species to gain access in

breeding sites. In 2018, N. nycticorax chose to nest

in mangrove palm near A. cinerea in which the trees

cannot be climbed and surrounded by ponds making

it difficult for predators and humans to reach their

nests. The conditions showed that to guarantee the

success of breeding, in addition to determining the

breeding time, clutch size; the safety factor appeared

to be a very decisive factor. Another factor which is

also a consideration for waterbirds is occurrence of

Aug Sep Oct Nov Dec Jan Feb Mar Apr Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr Jun Jul

Ardea cinerea ••••--•••--••••--•••--••••--•••--

Bubulcus ibis --•••---•••--•••---•••--•••---•••

Egretta alba - ••••--••••- ••••--••••- ••••--••••

Egretta garzetta --•••---•••--•••---•••--•••---•••

Nycticorax

nycticorax

----------------------••••--•••--

Phalacrocorax

sulcirostis

- ••••--••••- ••••--••••- ••••--••••

Year 2016

Species

Year 2017 Year 2018

Breeding Season of Waterbird in Tanjung Rejo, Deli Serdang Regency, North Sumatra, Indonesia

383

the rainy season. During the rainy season, farmers

and fishermen harvest which provide plenty of food

for waterbirds in the form of fish, insects, worms

and crustaceans. The presence of predators, the

optimum environmental conditions and the food

availability are factors that affect the breeding time

of birds, this will ensure the survival of both mother

and offspring (Prendergast, 2005; Passuni et al.,

2016; Jumilawaty and Andriayani, 2019).

3.2 Clutch Size

The observation on three heron species resulted in 1

– 4 eggs or clutch size per nets (Figure 1). The

difference in the clutch size is strongly influenced by

food factors, age of parents, species and geographic

area. The parent will lay eggs according to their

ability to ensure the survival and success of the

nestlings, especially regarding the food availability.

Female parents must be able to predict the number

of chicks produced and raised with environmental

conditions which exist when the breeding season

arrives. This number is the result of natural selection

that is adjusted to maximize the contribution of the

body of the female parent to the next generation and

is characteristic of each species and region (Barati et

al., 2008; Fernandez and Reboreda, 2008;

Jumilawaty and Aththorick 2016; Harriman et al.,

2017).

Figure 1: Clutch size per nest of waterbirds.

Based on the field observation, the food supply is

sometimes very varied and it is difficult to predict

whether the availability of food is sufficient as

expected, especially when raising a chick. As a

strategy to solve the limited food availability, some

species will only breed in a single breeding season,

Cormorants and generally other waterbirds have a

strategy by hatching their eggs not simultaneously

(asynchronous) using day breaks. This is intended to

be able to supply sufficient food for the chicks to be

hatched and raised and may guarantee the health of

the female parents (Jumilawaty, 2004; Harriman et

al., 2017).

Figure 2: Interval of egg-laying of waterbirds.

Clucth size is very closely related to the egg-

laying interval (Figure 2) and hatching (Figure 3).

The results showed that the egg laying interval

varied from 1 to 4 days (Figure 2). The strategy of

laying eggs and hatching by waterbirds is greatly

influenced by environmental factors, the physiology

of the female parent, age and experience of each

individual. The hatching of water bird eggs in

Tanjung Rejo occurs not simultaneously

(asynchronous) (Figure 3). This strategy is carried

out by birds to ensure that the waterfowl puppies get

adequate food and ensure the welfare of both the

mother and puppies that will be raised. This is

consistent with the results of research from Svagelj

et al. (2015) that the egg laying and hatching

intervals are highly dependent on the food source,

the physiology of the mother and its environmental

factors. Spawning and hatching intervals are

strategies of female parent to avoid predators (such

as eagles, snakes and monitor lizards) and human

disturbance. The spawning and hatching intervals of

water birds in Tanjung Rejo show no difference

when compared to the previous studes (Jumilawaty,

2004; Fernandez and Reboreda, 2008). This shows

that the pattern of egg laying and hatching of water

bird eggs is very dependent on environmental

factors.

IMC-SciMath 2019 - The International MIPAnet Conference on Science and Mathematics (IMC-SciMath)

384

Figure 3: Interval of hatching of waterbirds.

The experience and age of the parent also largely

determines the success of egg-laying and hatching

eggs. Generally for younger birds, it takes a little

time to learn to adapt to adjust the temperature to the

state of the environment. More young birds are

outside the nest and leave their eggs. In water,

hatching birds are carried out alternately between

males and females, but it cannot be distinguished

which one incubates the most. Bird age is thought to

be a factor in the incubation of incubation and

hatching of water bird eggs without differentiating

the sex. An equally important factor for the success

of breeding is the incubation period. The incubation

period is strongly influenced by environmental

factors between temperature and rainfall.

Temperatures that are too high and too humid will

cause the eggs to rot or fail to hatch. To overcome

unsuitable environmental conditions, the mother's

ability to incubate eggs requires a normal

temperature of 38C.

We also happened to count the duration of

incubation until hatching by the waterbirds. In

Figure 4, it can be seen that the incubation time for

A. cinerea and E. alba requires a longer time

compared to other species, in exception to B. ibis.

This is because the former two species have a larger

egg size compared to other eggs. The larger egg size

is attributed by its parents, having a size from 92-95

cm while other waterbirds have sizes between 40-55

cm. The results of this study are in accordance with

Figuerola and Green (2005) which states that the

length of the incubation period is strongly influenced

by the size of the bird's egg, the body mass of the

bird (g), the sex of the bird. Furthermore, Watson et

al. (1993) said that clutch size greatly influences the

egg-laying interval, hatching interval and incubation

period. It really depends on the physiology of the

female parents, despite of the presence of predator

and human disturbance. Birds will leave the nest if

there is interference and will return after feeling

safe. Noise caused by humans such as screaming and

other sounds will make the female parent disturbed

and leave the nest being incubated.

Figure 4: Number of hatchling(s) based on incubation time

(day).

4 CONCLUSIONS

The breeding season of waterbirds in Tanjung Rejo,

North Sumatra occurs twice in one year to coincide

with the rainy season and harvest season. The

quality of eggs to be produced and the ability of

chicks to survive is determined by the spawning

interval, hatching interval and the length of the egg

incubation period. The success of breeding water

birds is largely determined by the availability of

Breeding Season of Waterbird in Tanjung Rejo, Deli Serdang Regency, North Sumatra, Indonesia

385

food, the choice of breeding time, the choice of

nesting sites, temperature, weather (wind and rain),

parent experience, parent age and clucth size.

Another factor that also determines the success of

breeding waterbirds is the safety factor and avoid

predators.

ACKNOWLEDGEMENTS

The authors thank the Rector of Universitas

Sumatera Utara for the research funding in year

2017 and 2018 through TALENTA scheme.

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