Timing of breeding season of temperate passerines has been considered to be adjusted to their food availability. There is little work to reveal the cell stress responses of the nestlings hatched asynchronized with the food abundance peak, which is important for understanding the physiological link between the timing of breeding and the fitness of offspring.
Methods
Using gene expression level of blood HSP70 and HSP90 as indicators, we compared the cell stress response of Asian Short-toed Lark (Calandrella cheleensis) nestlings hatched under conditions of low, mid or high food (grasshopper nymph) availability in 2017.
Results
Nymph biomass, sample time and interaction of these two factors significantly influenced the blood gene expression level of HSP70 and HSP90 of Asian Short-toed Lark nestlings. HSP70 and HSP90 gene expression levels of the nestlings at 14:00 were significantly higher than those at 5:00. At either 5:00 or 14:00, the gene expression levels of HSP70 and HSP90 increase with the decrease of nymph biomass.
Conclusions
These results indicate that food availability is an important environment factor inducing cellular stress of Asian Short-toed Lark nestlings. The interactive effect of the nymph abundance and sample time on the HSPs response may be related with the daily temperature variation of the grassland. Over cell stress response may be one of physiological factor mediating the effect of food availability and the nestling's fitness.
The size of the nesting population of Ardeids and the distribution of their colonies in China has been continually under study. In southern China, Young and Cha (1995) described the dominant status of the Black-crowned Night Heron (Nycticorax nycticorax) in the Pearl River Delta, Guangdong Province as well as the location of colonies in this area. Wong et al. (2004) discovered 44 nesting colony sites in Guangdong, Guangxi and Hainan provinces. In Hainan, Liang et al. (2006) reported up-to-date information of nesting Ardeids on this island. In other parts of China, Fasola et al. (2004) revealed a large population of Ardeids in the Yangtze River area, while Zhu and Zou (2001) listed 127 nesting colony sites in China. However, none of these published papers covered Guizhou, a province in southwestern China whose topography is characterized by a mixture of hills and cultivated basin lands. In addition, Ardeids and the location of their nesting colonies in this province may be affected by the belief of some indigenous populations that these waterbirds are often regarded as lucky or unlucky creatures (Liang, pers. comm.). Ardeids and their nests are disturbed once they are spotted in villages and farmlands. Given that the locations of Ardeid nesting colonies are poorly known and their distribution probably affected by the culture of the local people, a survey was conducted in 2006 to establish the current status of nesting Ardeids in this province. Hence, we report on the distribution of nesting colonies and the abundance of their nests in central Guizhou. Conservation advice on protecting important colonies is also provided.
Study area and methods
Study area
Guizhou Province (24°30′–29°13′N, 103°31′–109°30′E) is situated in the southwestern part of China and covers an area of 176100 km2, accounting for 1.83% of the total area of the Peoples' Republic of China. The average elevation is 1100 m. Mountains and hills make up 92.5% of the total provincial area. Most upland areas are located in the west, where the elevation ranges between 1500 and 2800 m. The middle part of the province has an average elevation of around 1000 m. In the north, east and south the average elevation drops to 500 m. The climate of Guizhou is dominated by subtropical monsoons, i.e. wet summers and dry winters. The mean temperature ranges from 3℃ in January to 26℃ in July. Annual rainfall varies between 1100 and 1400 mm.
The western part of the province is dominated by grazing lands, while the other parts are covered by extensive terraced fields, where rice, rape, cereal and maize are cultivated. The total area of agricultural farmland is about 17694 km2. Given that Guizhou is a hilly province, farmlands are generally located in the valleys between mountains and in terraced areas. During the survey period, the main crops growing were rice, wheat and vegetable. Rice fields are permanently inundated, while the wheat and vegetable fields were dry, at a typical height of about 0.6 m, which is too overgrown for egrets and herons to feed. Other potential feeding habitats were low-lying streams and, depending on rainfall, seasonally inundated abandoned farmlands.
Field methods
Known nesting colonies in central Guizhou were surveyed between 5 and 12 May 2006 (Table 1, Fig. 1). New colonies were located by 1) confirming previous observations suggestive of breeding activity, 2) while traveling between colonies and 3) reports from villagers. Each nest, containing either incubating adults or the presence of chicks, was considered as one nest and it was counted by direct observation. The number of nests of a species was taken to be the sum of the number of nests of that species in each colony. In addition, the types of habitat of nesting colonies, broadly classified as feng shui wood, woodland, bamboo and gardens, were recorded. A feng shui wood is defined as lowland woodland behind villages, preserved for reasons of Chinese geomancy (Corlett et al., 2000).
Table
1.
Number of nests and survey dates of surveyed colonies in central Guizhou, China, between 5 and 12 May 2006
Colony
Survey date
Elevation (m)
Habitat type a
Little Egret
Cattle Egret
Black-crowned Night Heron
Chinese Pond Heron
Grey Heron
Total
% b
1. Yanfu Resort
5 May
250
A
361
18
84
463
29.2
2. Tiantai
5 May
301
B
50
64
114
7.2
3. Wanglong
5 May
310
B
90
5
95
6.0
4. Guandu
5 May
319
B
70
70
4.4
5. Yangliu Primary School
6 May
881
B
2
19
21
1.3
6. Luobolin
6 May
868
B
10
2
12
0.8
7. Chenxing Village
6 May
852
B
2
13
15
0.9
8. Xinping Primary School
7 May
806
B
7
34
41
2.6
9. Fengyunyan
7 May
750
C
53
344
69
466
29.4
10. Maqiao Village
12 May
923
B
48
76
6
50
180
11.3
11. Baihua Lake
12 May
1233
D
96
12
2
110
6.9
Total
789
94
434
268
2
1587
100.0
Per cent (%)
49.7
5.9
27.3
16.9
0.1
100.0
a In habitat type, A, secondary woodland and bamboo; B, feng shui wood; C, woodland and gardens; D, secondary woodland dominated by pine trees. b % = relative abundance
Figure
1.
Survey route and locations of nesting colonies (black dots) in central Guizhou, China (insert: the location of Guizhou in China (shaded area))
During the survey, a total of 1587 nests of five Ardeids, i.e. Little Egret (Egretta garzetta), Cattle Egret (Bubulcus ibis), Chinese Pond Heron (Ardeola bacchus), Black-crowned Night Heron (Nycticorax nycticorax) and Grey Heron (Ardea cinerea) in 11 nesting colonies were all found in the northern part of Guizhou (Table 1, Fig. 1, Plate Ⅰ). A previous active colony at Daizhang Village, Huangping County was visited but only Chinese Pond Herons were found and no breeding activity was observed. No colonies were found at Leigongshan Nature Reserve and its nearby areas, i.e. Xijiang Town, Leishan County in the southern part of Guizhou, where rice fields were present (Fig. 1).
Plate Ⅰ.
Cattle Egret (Bubulcus ibis) showing breeding plumage (a) and feeding young (b), and Chinese Pond Heron (Ardeola bacchus) showing breeding plumage and color of legs (c) and young (d) (Photos by Xiaojie Su)
The largest colony was found at Fengyunyan (No. 9 in Table 1, accounting for 29.4% of the total number of nests), while the smallest was at Luobolin (No. 6, 0.8% of total number of nests, Table 1). The Yanfu Resort colony (No. 1) contained the largest number of Little Egret nests (56% of the total number of nests of this species). The Fengyunyan colony contained the largest number of Black-crowned Night Herons (80%) and Chinese Pond Heron nests (26%), while the Maqiao Village colony (No. 10) was the largest nesting site of Cattle Egrets (81%).
Numerically, Little Egret was the dominant breeding species (49.7% of the total number of nests) and Grey Heron the least abundant (0.1%) (Table 1). Little Egret was also the most widespread breeding species for it bred in all colonies. The Chinese Pond Heron bred in all colonies, except those at the Yanfu Resort and Guandu (No. 4). The Cattle Egret and Black-crowned Night Heron bred in two or three colonies, while the Grey Heron bred only at the Baihua lake colony (No. 11).
Nesting habitat and elevation
In central Guizhou, eight nesting colonies were situated in feng shui woods (Table 1). Woodland and artificial gardens were recorded at Baihua Lake and Fengyunyan. Bamboo was an addition to the vegetation type of colonies at the Yanfu Resort. Nests in feng shui wood colonies were built on trees about 10–20 m high. All colonies were located at elevations of 250 m or higher. The highest colony recorded in the survey was at Baihua Lake (1233 m), while the lowest was at Yanfu Resort (250 m).
Protection status
No colonies are officially protected. They appear to be accepted by the local villagers and landowners, as no signs of disturbance were observed during the survey. In the Yanfu Resort, the footpaths of this private property are not open to the public and accessibility to this site is restricted. However, this island colony is still accessible via river transport. The colony at Fengyunyan is indirectly protected by its status as a theme park. This site is walled and an admission fee is charged. Thus, these two colonies are restricted to the public.
Discussion
The present survey showed that, in central Guizhou, egrets and herons were mainly nesting in the northern part of this province and, in particular, no Ardeid nesting colonies were found in the southern part of Guizhou (i.e. Leigongshan Nature Reserve and Xijiang Town). The distribution pattern of Ardeid nesting colonies is apparently affected by the location of ricefields, which is the key feeding habitat of nesting egrets and herons elsewhere (Kushlan, 2000). Although no land use statistics for Guizhou are available for making a comparison, ricefields (summer wet crop) were generally present around the colonies during the survey. In contrast, nesting colonies were absent from areas dominated by wheat and vegetable fields (winter dry crop). For instance, no activities of egrets and herons were seen along the 70 km stretch between Renhuai to Xishui, an area dominated by dry winter crops during the survey. Local experience revealed that the crop rotation periods vary between years and is greatly affected by rainfall patterns. Rice is planted later if the rainy season (from April to August) starts late and the rainfall is light. During the survey period, it was noted that there was little rainfall, which had started later than normal – in May, and therefore most farmlands were still dominated by dry winter crops. It is likely therefore, that the number of nests may be lower than in previous years. Also, it is expected that the nesting birds will suffer from prolonged drought during early breeding seasons due to inadequate wet feeding habitats if the rainy season in Guizhou is delayed.
To our surprise, during the survey from Kaili City to Leishan County, the southern part of Guizhou Province, where prime feeding habitats are present, no egrets or herons were seen in ricefields or large rivers. Locals reported that egrets and herons are considered to be unlucky creatures in this region and therefore, they are disturbed immediately if they are spotted around villages. Thus, the traditional culture of the local people might be another important factor influencing the distribution of nesting colonies in Guizhou. However, further investigations on this issue are needed and more data should be collected.
Only about one-third of the total area of Guizhou was surveyed in this study, but it already indicated that nesting egrets and herons could make use of flatlands in the basin and terraced ricefields in this relatively hilly province. It is suggested that a territory-wide survey should be conducted to assess the total nesting population in this province and to identify the most important colonies for conservation. Based on the findings of this survey, conservation priority should be given to the colonies at Yanfu Resort and Fengyunyan, which contained about 70% of the total number of nests in central Guizhou. These two colonies should be designated as official protected areas. Currently, they are unofficially protected by their status of private ownership and controlled access. Stationing authorized persons at the colonies, who could prosecute hunters, should be considered. Priority should also be given to protecting the largest colonies of the Chinese Pond Heron and Cattle Egret at Tiantai and the Maqiao Village.
Acknowledgements
We would like to express our gratitude to Dr. Lew Young and Mike Kilburn for their comments on the earlier draft. We also thank Zhigang YU and Hong JIANG from the Guizhou Institute of Biology, China, for their help during the survey. The cost of this study in Guizhou was covered by Hainan Normal University.
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Table
1.
Number of nests and survey dates of surveyed colonies in central Guizhou, China, between 5 and 12 May 2006
Colony
Survey date
Elevation (m)
Habitat type a
Little Egret
Cattle Egret
Black-crowned Night Heron
Chinese Pond Heron
Grey Heron
Total
% b
1. Yanfu Resort
5 May
250
A
361
18
84
463
29.2
2. Tiantai
5 May
301
B
50
64
114
7.2
3. Wanglong
5 May
310
B
90
5
95
6.0
4. Guandu
5 May
319
B
70
70
4.4
5. Yangliu Primary School
6 May
881
B
2
19
21
1.3
6. Luobolin
6 May
868
B
10
2
12
0.8
7. Chenxing Village
6 May
852
B
2
13
15
0.9
8. Xinping Primary School
7 May
806
B
7
34
41
2.6
9. Fengyunyan
7 May
750
C
53
344
69
466
29.4
10. Maqiao Village
12 May
923
B
48
76
6
50
180
11.3
11. Baihua Lake
12 May
1233
D
96
12
2
110
6.9
Total
789
94
434
268
2
1587
100.0
Per cent (%)
49.7
5.9
27.3
16.9
0.1
100.0
a In habitat type, A, secondary woodland and bamboo; B, feng shui wood; C, woodland and gardens; D, secondary woodland dominated by pine trees. b % = relative abundance
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