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Paving the way towards unbearable: what do shorebird embryos tell us on Sri Lanka’s newfound paving ritual

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Seneviratne & Jayasinghe Paving the way towards unbearable
Paving the way towards unbearable: what do shorebird embryos tell us on Sri
Lanka’s newfound paving ritual
Sampath Seneviratne* and Shashiprabha Jayasinghe
Avian Evolution Node, Department of Zoology and Environment Sciences, Faculty of Science,
University of Colombo, Colombo 03 *(sam@sci.cmb.ac.lk; +94710-821177)
The past century shows a rapid rise in earth’s surface temperature across the globe with significant
regional variations due to deforestation and urbanization, which both contribute heavily towards
elevating global warming through greenhouse effect (Wallington et al. 2004, Riebee 2007).
Todays earth the warmest in its recorded history. Although the life on earth, in general depends on
earth’s temperature for its survival, the life that associates with the surface, mainly for breeding
such as ground nesting seabirds and shorebirds (Order Charadriiformes), could have a much
greater sensitivity to the alterations of the earth’s temperature.
The constancy of the temperature in the internal environment (commonly known as ‘temperature
homeostasis’) is vital for the survival of any biological system. Therefore the ectothermic embryo
of otherwise endothermic birds requires a mechanism to mitigate the extreme temperatures in
order to avoid the vulnerability to hyperthermia or hypothermia (Brown and Downs 2002, Hiebert
& Noveral 2006). Since the parent birds need to maintain their own body condition as well as the
microclimatic conditions of the nest, the incubation period is considered as a high energy-
demanding period for ground nesting birds (DuRant et al. 2010, Deeming 2002a).
Suburban sprawl and deforestation are two main reasons for the rise of local temperature across
the globe. Although the terrestrial life on earth depends heavily on its temperature for survival,
the life that associates with earth’s surface, such as ground nesting shorebirds (Order
Charadriiformes, commonly known as ‘waders’ in Sri Lanka), could have a greater sensitivity to
the alterations of the earth’s surface temperature. Using an automated data logger here we
critically evaluated the effect of ground (substrate) temperature on temperature homeostasis of the
egg of a ground-nesting shorebird (Red-wattled Lapwing - Vanellus indicus) found in a wide
range of environments, from city parks and parking lots to undisturbed forested wetlands. Our
study sites spans across the island from Colombo, Mannar Island, Puttalum, Galle, Kandy,
Central Highlands to Bibilea in the eastern foothills. We found that the bottom substrate of the
nest has a significant impact on the nest microclimate and embryonic survival. Our data logger
registered extremely high surface temperatures at urban areas when the habitat is altered with
concrete tiles (e.g. Nawala Wetland Park; peak ground temperature 510C peak air temperature is
340C). Natural materials that mimic concrete tiles, such as stone and pebbles had increased the
nest temperature in natural nests as well. Grass and sand provided the optimum temperatures for
the survival of embryos in the studied nests throughout the island. Sandy surfaces of Mannar
Island, which considered as the warmest area in the country, had mild temperatures and narrow
daily temperature fluctuation when compared with urban areas. Concrete-paved urban landscapes
showed high daily fluctuation in ground temperature, which resulted in nest failure due to
exceeding the tolerant range (33–40°C). Our findings exposed an overlooked aspect of the urban
landscape that affects the wellbeing of the life associating with it are we paving our cities to
make it unbearable for life to exist?
Seneviratne & Jayasinghe Paving the way towards unbearable
The natural pavement of Sri Lanka is the lush green grass, though most of that are introduced
grasses, it gives the island its reputation of the emerald island. The sand in coastal belt, exposed
earth, rocks and pebbles mainly along large rivers and decomposing foliage being the other natural
pavements in the landscape. These same materials had been used for artificial pavements ever
since ancient civilizations of Sri Lanka, which dated over two millennia. Tarred roads characterize
both urban and rural motor-able road network of the island.
Town planners of the island recently started to show a great interest in paving interlocked concrete
blocks as a substitute for all of the above types of pavements. The use of concrete tile pavements
ranging from roads in rural sector, jogging tracks and walkways in the urban setting, roadside
pedestrian walkways, parking lots to public spaces. Thus the interlocked concrete pavement
replaces both artificial pavements such as tar pavements and dirt roads as well as natural cover
such as green belts and lawns. Are these concrete pavements contributed towards the alarming rise
of local temperature? How smart are we, as a nation to transform the landscape in this manner in
the face of global warming? Is it sustainable? Is it healthy?
We placed an automated data logger to evaluate the effect of different pavements on temperature
homeostasis of the embryo of a ground-nesting shorebird (Red-wattled Lapwing (Vanellus
indicus)) found in a wide range of environments, from city parks and parking lots to undisturbed
forested wetlands, in varied ground temperature regimes.
The objective…
We test the effect of substrate material ranging from grass, sand, pebbles, stones to concrete tiles
on the temperature regulation of the egg of ground-nesting lapwings from Colombo and Mannar
(naturally high ground temperature) to Nuwera-Eliya (naturally low ground temperature). We test
the highest and lowest temperatures, the level of temperature fluctuation, the embryonic survival
and the changes of parental investment under the changing surface temperature to objectively
evaluate the effects of substrate on the life that depends on it.
What we did …
We developed a thermal sensing data logger with four DS18B20 type thermal sensors (Jayasinghe
2016) to measure egg temperature (TE; off the egg shell), ground temperature (TG; 1cm below
ground near the nest) and air temperature (TA; 10cm above ground near the nest) in 5 minutes
intervals for up to 72 hours in lapwing nests. Fieldwork was conducted during February to
December in 2015 from Colombo, Mannar Island, Puttalum, Galle, Kandy to central highlands and
Bibilea in the eastern foothills, covering all major climatic regions of Sri Lanka (low country -
annual mean temperature (amt) of 30-34oC; mid country - amt 18-33oC and up country amt 13-
25oC) (Jayasinghe 2016).
We also observed the behaviour of parent birds of each nest from a portable hide, located ~50m
away from the nest using binoculars. Upon collecting above data we measured the substrate of the
nest (Hoyt, 1979 and Hegyi, 1996). To set the thermal end points a set of 20 fertilized chicken
eggs were incubated in a temperature and humidity controlled incubator at the laboratory (Roche
et al. and Meir et al., 1990). A group of 5 eggs were treated daily by applying a high temperature
of 42.0oC and another 5 were treated by applying a lower temperature as 20.0oC for one hour until
they hatched out. The range of temperatures was obtained from our empirical data from the field
(see above). The remaining eggs (n=10) were incubated in the incubator at 37.00C as the control
group (Hiebert et al. 2006).
Our results and what it mean…
We observed 29 eggs in 17 nests in six locations. The mean egg temperature under parental
incubation (35.7oC ± 1.6) is significantly different from that of the absence of parental incubation
Seneviratne & Jayasinghe Paving the way towards unbearable
(33.9oC ± 5.1; t196 = 4.27, p < 0.05). The temperature variability is also higher in the absence of the
parent (28.3–42.5°C; incubating eggs ranged from 32.9–40.2°C), and in the absence of the parent
it fluctuates out from the viable range for a developing egg (Fig. 1). When the egg exposed to an
extreme low temperatures (<20°C) or to an extreme high temperatures (>42°C), the survivorship
of the developing embryo drops under laboratory conditions. At 20.0°C, the hatching rate is 40%
and the embryo development rate is 60% with many developmental abnormalities. At 42.0°C the
embryo development rate dropped to 0% hence none of the eggs hatched (Fig. 2).
At the studied locations the daytime and nighttime temperatures were significantly different from
each other (Table 1). The Colombo municipality area with the concrete tiled pavements had the
highest daytime temperatures (Nawala Wetland Park; T
!=50.7!°C, T
!=33.C). Peradeniya
University, another suburban area in the highlands, which has concrete tiles, had the second
highest temperature (T
!=42.C, T
!=30.C). Although we initially thought that the Mannar
Island could be the warmest because of its general climate, our data loggers recorded that it has
mild temperatures and narrow daily temperature fluctuation when compared with urban areas
(T
!=37.C, T
!=34.C; Table 1). Therefore the natural shoreline of Mannar provides the
optimum temperatures for embryo development, this may be probably a reason for many species
of ground nesting birds to breed in large numbers in Mannar (e.g. Seneviratne et al. 2016). The
lowest temperatures were recorded in the foothills in Bibilea (T
!=23.C, T
!=24.C). Our
field data suggests lapwings did not breed in areas where the ground temperature is below 20°C.
The bottom substrate (grass, sand, earth, pebbles and concrete paving blocks) has a significant
impact on the nest microclimate (F2,196 = 268.5, p < 0.05; Fig. 3), and it contributed to the
embryonic survival. When the substrate is grass, earth or sand, the surface temperature did not rise
above the tolerant limits even under very high ambient (air) temperatures. However when the
substrate is either pebbles (natural) or concrete tiled (artificial) then it fluctuates rapidly and goes
beyond the upper limits in the middle of the day.
We think…
We found extremely high surface temperatures when the habitat is altered with concrete paving
blocks (e.g. Nawala Wetland Park). Stones and pebbles, that are somewhat similar in properties to
concrete, also increased the nest temperature in natural habitats. Grass and sand provided the
optimum temperatures for the survival of embryos in the studied nests throughout the island.
Urban landscapes showed high daily fluctuation in ground temperature, which resulted in nest
failure due to exceeding the tolerant range. Therefore we believe that the trend of paving the
surface with concrete tiles, as it is happing in an alarming rate across the country both in the urban
and rural setting, is unsustainable. Concrete paving blocks create temperatures that exceed natural
tolerance levels in these embryos. We argue, if it is intolerable for a well-adapted ground bird, then
it may not tolerable for the other life forms as well – including the creator (of concrete). Our study
exposed an overlooked aspect of the urban landscape that affects the wellbeing of the life
associating with it, where future city planners should pay a more careful attention.
Seneviratne & Jayasinghe Paving the way towards unbearable
Figure 1: The fluctuation of the egg temperature (!
!) with parent bird (blue line) and without
parent bird (red line) against the ground temperature (!
!) in nests of Red-wattled Lapwing. Red,
blue and yellow arrows indicate the range of !
! of the non-incubating egg, incubating egg and the
amount of parental investment respectively.
!
Figure 2: Percentage development of embryos under each temperature treatment (Blue 22oC,
Orange 37oC, Green 42oC).
Seneviratne & Jayasinghe Paving the way towards unbearable
Figure 3: The effect of the substrate (see methods) on the ground temperature (TG) measured from
the thermal sensor in lapwing nests.
Table 1: Mean Air, Ground and Egg temperatures in different locations
Lcation
Temperature (C) (n = number of hours)
TA
TG
Anawilundawa
26.67 (135)
24.66 (132)
26.67 (135)
24.66 (132)
Bibile
23.72 (59)
21.77 (132)
23.72 (59)
21.77 (132)
Colombo
33.67 (1228)
28.38 (702)
33.67 (1228)
28.38 (702)
Hiyare
29.89 (96)
25.61 (132)
29.89 (96)
25.61 (132)
Mannar
36.80 (406)
30.48 (264)
36.80 (406)
30.48 (264)
Peradeniya
30.79 (321)
22.37 (264)
30.79 (321)
22.37 (264)
Bold text indicates the nighttime temperatures (0700PM-0555AM) while the others indicate the day time
temperatures (0600AM-0655PM).
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