The study of reproductive biology and the estimation of nest survival rates are critical to understanding avian life history (Martin, 2004; Stutchbury and Morton, 2008, 2023). Life history traits related to reproduction, such as clutch size, parental care, chick development, and survival rate, can provide insights for solving problems related to the assessment of population status and conservation (Martin, 2002, 2008; Martin et al., 2017). Most recent studies on reproductive biology have focused on northern temperate zone birds (Martin, 2004; Lloyd et al., 2014; Xiao et al., 2017), while birds in other regions, especially tropical birds, have been relatively less studied (Xiao et al., 2017). The main reason may be that tropical birds are relatively difficult to monitor (Martin, 1996; Jiang et al., 2017; McCullough and Londoño, 2017). Studies have shown that the reproductive strategies of birds in different regions are different mainly due to the differences in the breeding habitats of birds and their nest predation rates (Martin, 1996). Compared with temperate birds, tropical birds are characterized by a longer breeding season, smaller clutch size, longer brooding, and hatching periods (Martin, 1996; Lloyd et al., 2014). Therefore, expanding the understanding of the life history of tropical birds can help us better understand the global trend of life history strategies (Ricklefs and Wikelski, 2002; Slevin et al., 2020).

Nest predation is a major factor limiting the success of bird reproduction and affects the life history and population dynamics of birds (Reidy and Thompson, 2012; Thompson and Ribic, 2012; Ibáñez-Álamo et al., 2015; Chen et al., 2020). Especially for ground-nesting birds, nest predation has become one of the most critical factors affecting their reproductive performance and population growth (Sanders and Maloney, 2002; MacDonald and Bolton, 2008; Pedersen et al., 2011; Melville et al., 2014). Based on this, understanding predation on birds and its influencing factors is of great significance for studying bird population dynamics and proposing conservation strategies (Martin, 1993; Chalfoun et al., 2002; Seibold et al., 2013; Chen et al., 2020).

The red junglefowl (Gallus gallus) belong to the genus Gallus of the pheasant family (Phasianidae) in the order Galliformes and is a ground-active bird (Zheng, 2022). According to the differences in their distribution range and morphological characteristics, the world’s red junglefowl can be divided into five subspecies, all of which are distributed in southern Asia (Johnsgard, 1999; del Hoyo et al., 2001). There are two subspecies in China, the southern Yunnan subspecies (G. g. spadiceus) and the Hainan subspecies (Gallus gallus jabouillei; Zheng, 2022).

In this study, we searched and monitored the natural nests of red junglefowls, the Hainan subspecies, in Datian and Bangxi Nature Reserves, tropical Hainan Island, China, using infrared cameras. Considering that the number of natural nests of Galliformes birds is limited and nest sites are relatively difficult to find (Luo et al., 2017), the use of artificial nests for simulation studies can not only reduce human interference on hatching in the wild but also has the advantage of ease of use, and can provide sufficient samples for research (Martin, 1987; Major and Kendal, 1996; Wilson et al., 1998; Zanette and Jenkins, 2000; McDonald et al., 2009; Melville et al., 2014; Luo et al., 2017), we carried out artificial nest experiments in the study area to compare the survival rates and potential predators of natural nests and artificial nests.

In the two breeding seasons of 2020 and 2021, we found a total of 16 natural nests and nesting success of the red junglefowl was 31.25%, which was higher than the result observed by Yuan (2009) in the same area (18.2%). However, the rate of nest abandonment was as high as 68.75%, higher than the results of previous studies (55.6%; Yuan, 2009).

In a study of the Indian subspecies, it was found that after the first reproductive failure, red junglefowls would choose to reproduce a second time (Collias and Collias, 1967). Similarly, the reproduction record of the southern Yunnan subspecies also mentions that it may reproduce twice a year (Zheng et al., 1978). It is likely that the Hainan subspecies may reproduce multiple times to improve the reproductive success, which needs further confirmation in the wild. The clutch size in our study areas was similar to that of the Indian subspecies (Anwar et al., 2016) but was significantly lower than that of the southern Yunnan subspecies (Zheng et al., 1978). In southern Yunnan, female and male birds brood and hatch eggs together (Zheng et al., 1978). Yuan (2009) observed that in the field, both male and female birds brood nestlings, while we found that only female birds were responsible for brooding in the wild.

We found that the Hainan subspecies was breeding from March to July, and that the number of broods was highest in April. It is thus speculated that the breeding peak in the Hainan subspecies is April. This is consistent with the results of Yuan (2009), but there are differences between the Indian subspecies from different areas and the southern Yunnan subspecies. For example, in India, broiler flocks were found to breed in January–October, and the breeding peak period was March–May (Ali and Ripley, 1987; Anwar et al., 2016); in the Malay Peninsula region, the breeding time is from December to May of the following year, and the breeding peak is from January to February (del Hoyo et al., 2001). In areas with sufficient food, red junglefowl can even breed year-round (Arshad and Zakaria, 1999). In southern Yunnan, the breeding time is from February to October (Zheng et al., 1978). Tropical birds have different life history traits (Stutchbury and Morton, 2023). Anyway, we only carried out the breeding monitoring of the red junglefowl for 2 years, which may be the reason that the breeding season in Hainan subspecies differs from other subspecies. There should be a long-term monitoring to the subspecies in the wild.

Studies have found that red junglefowl tend to choose areas with well-developed herbs and patches for nesting (Collias and Collias, 1967). However, some studies have suggested that deciduous trees and bamboo forests with scattered patches are the favorite nesting habitats of red junglefowls during the breeding season (Johnson, 1963). In this study, it was observed that female birds mostly nested on patrol roads or in open areas near the edge of forests with fewer deciduous leaves. This reflects the geographical differences in the selection of nesting sites among different subspecies. The edge effect hypothesis indicates that because the edge area of the habitat has more abundant vegetation resources and a more complex environment, the predation pressure is usually greater than that of the central area (Ewers and Didham, 2007). However, studies on the Reeves’s pheasant (Syrmaticus reevesii) do not support this hypothesis, as this species tends to nest in marginal areas with more human interference (Luo et al., 2017). Our results are consistent with that study, as the female birds of the Hainan subspecies chose to nest on patrol roads or at the edge of the forest. It is possible that human activities in these areas are more frequent, and some predators are forced to enter the central area where there are fewer disturbances, thereby reducing predation by natural enemies. Nest predation is the main factor in the failure of pheasant reproduction (Lu and Zheng, 2001; Sherry et al., 2015). In the predation events we observed, eggshells were either left in the nest or no trace of the predator was left after the eggs were preyed upon. Therefore, we speculated that rodents and reptiles may be the main nest predators. This is because rodents usually leave eggshells or debris behind after predation, and some reptiles leave no traces when preying on nests (Klug et al., 2010). In addition, in the study area, small carnivorous mammals, such as leopards, falcons, and raptors are the main natural enemies of the subspecies (Zheng et al., 1978; Evans et al., 1993), and snakes are also the main predators of red junglefowls (Anwar et al., 2016).

In our study, although artificial nests were set up in the same study area, their predation rate was lower than that of natural nests, and the types of predators were also different. This result is consistent with the results of a study of the reed parrotbill (Paradoxornis heudei) (Chen et al., 2020). This is different from the results of other studies. For example, snakes were found to be the main predators of natural nests, while mammals were found to be the main predators of artificial nests (Thompson and Burhans, 2003; Chen et al., 2020).

The use of infrared camera technology to monitor artificial nests is ideal for the determination of nest predator species (Anthony et al., 2006; Kross et al., 2013). In this study, the infrared cameras captured a number of wild animals, such as greater coucals, lesser coucals, and Hainan Eld’s deers. Among them, the greater coucal was the main predator of the experimental eggs, and the feeding activity of Hainan Eld’s deers caused female birds to abandon nests. Studies have shown that wild boars can change the terrain by overturn large areas of soil, thereby changing the vegetation structure and composition of their habitats (Singer et al., 1984; Lacki and Lancia, 1986), which is particularly harmful to ground-nesting birds (Barrios-Garcia and Ballari, 2012; Sanders et al., 2020). Therefore, the wild boar may be an opportunistic predator of nests. A recent study has shown that gray squirrels (Sciurus carolinensis) are widely considered to be important predators of bird eggs and chicks (Broughton, 2020). We photographed red-bellied squirrels in the vicinity of artificial nests many times and speculate that the red-bellied squirrel is a potential nest predator. In addition, studies have found that bats are the main nest predators of tropical forest birds (Perrella et al., 2019). In our study, we did not find predation of eggs by bats. In follow-up work, we intend to carry out effective and continuous monitoring of breeding nests and clarify the antipredation strategies of red junglefowl.

In this study, the predation rates of artificial nests varied in Datian. The main reason is that the artificial nest experiments were done at the buffer zone in 2020, while at the core zone in 2021. The habitats in the two regions are significantly different, and so are the predation rates. The predation rate was 0% in Bangxi. There are two possible reasons. Firstly, our sample size is not large enough, secondly, there is a relative lack of potential predators for red junglefowl eggs. Although the survival rates of the artificial nests in the two study sites were higher than those of the natural nests. The possible reason is that the experiment was conducted in May 2020, while in March 2021, the birds had just started breeding, and most of them were in the hatching period in May. Most previous studies used the quadrat survey method (Johnson, 1963; Kalsi, 1992; Arshad and Zakaria, 2009; Yuan et al., 2009a,b) or radio tracking technology (Arshad and Zakaria, 2011) to investigate habitat selection and habitat utilization in red junglefowls. Satellite tracking technology is a tool to effectively track the small-scale movement of highly mobile and inaccessible species (Cagnacci et al., 2010; Coxen et al., 2017). The application of this technology to the study of ground-dwelling pheasants such as red junglefowl is very important for understanding how these birds use their habitat, the motivation for their movements, and the process of space utilization, to ultimately improve pheasant protection.

Red junglefowl are ground-nesting pheasants that are highly alert, which makes field research and tracking difficult (Arshad and Zakaria, 2011; Anwar et al., 2016). Human interference or direct observation of brooding parent birds may lead to abandonment of the nest and reproduction failure (Yuan, 2009). Therefore, there is limited information on the survival rate of red junglefowl nests. Protecting the habitat and reducing human disturbance will play a positive role in the growth of the red junglefowl population in our study areas. Datian and Bangxi are both protected areas with the main goal of protecting Hainan Eld’s deer. Burning grassland vegetation, thinning, plowing, and manual removal of waste can alleviate the degradation of Hainan Eld’s deer habitat quality (Fu et al., 2016, 2018). We suggest that the conservation area should take into account the impact on the reproduction of ground-dwelling pheasants when rebuilding or reconstructing the suitable habitat of Hainan Eld’s deer. In addition, domestic chickens were photographed in the Bangxi Nature Reserve, indicating the possibility of hybridization between wild red junglefowl and domestic chickens. It is recommended that free-range domestic chickens be banned within protected areas to avoid the problem of genetic contamination of wild red junglefowls.

The original contributions presented in the study are included in the article/Supplementary material, further inquiries can be directed to the corresponding author.

Ethical review and approval was not required for the animal study because we have obtained the administrative licensing decision of Hainan Forestry Bureau on the study of Red Junglefowl [Hainan Forestry Bureau approval (2019) 083].

XR designed the study. XR, JL, BH, HW, GW, and TT carried out field experiments. XR and QL performed cartography and statistical analyses. XR wrote the draft manuscript. All authors contributed to the article and approved the submitted version.

This work was supported by the Joint Fund of the Natural Science Foundation of Hainan Province (no. 320RC506 to XR) and the National Natural Science Foundation of China (no. 31800320 to XR). XR was funded by the project supported by the Scientific Research start-up Fund of Hainan University [no. KYQD (ZR) 20057] and the Teaching Research of Hainan University (no. Hdsz20-9).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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