The breeding information of most birds in Asian tropical areas,especially in limestone forests,is still poorly known. The Streaked Wren-Babbler (Napothera brevicaudata) is an uncommon tropical limestone bird with a small range. We studied its nest-site selection and breeding ecology,in order to understand the adaptations of birds to the conditions of tropical limestone forest in southern China.
Methods
We used methods of systematical searching and parent-following to locate the nests of the Streaked Wren-Babbler. We measured characteristics of nest sites and rock cavities. Data loggers and video cameras were used to monitor the breeding behavior.
Results
All the observed nests of the Streaked Wren-Babbler were placed in natural shallow cavities or deep holes in large boulders or limestone cliffs. The great majority (96.6%) of Streaked Wren-Babbler nests had three eggs with an average fresh weight of 3.46 ± 0.43 g (n = 36,range 2.52?4.20 g). Most (80.4%) females laid their first eggs between March and April (n = 46). The average incubation and nestling period of the Streaked Wren-Babbler was 10.2 ± 0.4 days (n = 5,range 10?11 days) and 10.5 ± 0.8 days (n = 6,range 9?11 days),respectively. Most (87.9%) nests had at least one nestling fledge between 2011 and 2013 (n = 33).
Conclusions
Our study suggests that several features of the breeding ecology of the Streaked Wren-Babbler,including building nests in rocky cavities,commencing breeding earlier than most species,and reducing foraging times during the incubation period,are well-adapted to the unique habitat of tropical limestone forest.
If there is gradual loss of feathers during the annual cycle following the complete molt, we should expect a gradual reduction over time. Brodkorb (1985) reported that house sparrows Passer domesticus loose 11.5% of their feathers from winter to summer, although the data were cross-sectional rather than longitudinal. Hence these data do not allow separation of phenotypic plasticity from selective disappearance. Here I propose predictions that would help discriminate between alternative explanations for seasonal change in the number of feathers. If individuals with more feathers do better in terms of insulation than individuals with few feathers, we should expect an increase in the number of feathers during fall and winter as temperatures fall. If feathers provided protection against predators by allowing for escape, we should expect an increase in the number of feathers over time because individuals that have lost feathers due to predation were more likely to subsequently be captured by a predator or die from insufficient insulation. If the sole advantage of more feathers was simply to provide better insulation, we should expect isometry. If there were relatively more feathers on small species due to their high surface to volume ratio, we should expect negative allometry for the number of feathers. If the total mass of feathers showed isometry, we should expect that the number of feathers and the mean mass of feathers should show isometry.
The objectives of this study were to (1) estimate the allometry of number, total mass of the plumage and mean mass of feathers and (2) to model changes in the number of feathers during the annual cycle to better understand the temporal patterns of feather loss. The number of feathers should reach a maximum at the end of molt, when all feathers including missing ones have been replaced, the only exception being feather loss at the stage of molt. Any subsequent loss of feathers following molt should result in a reduction in the total number of feathers. In contrast, a subsequent increase in the number of feathers later during the year would only be possible if individuals with more feathers survived better than individuals with fewer feathers. Alternatively, individuals may grow more feathers during fall and winter although there is no empirical evidence so far for such seasonal growth of feathers. Thus, a seasonal increase in the number of feathers would represent an estimate of the selective advantage of having more feathers with individuals with few feathers disappearing from the population. The data used for this study mainly derived from Wetmore (1936), who pioneered the study of abundance of feathers on birds.
Methods
Data
Data on the number of feathers and their total mass were extracted from Wetmore (1936) combined with smaller samples from Staebler (1941), Brodkrob (1955) and Markus (1965). Although the mass of different types of feathers would have been useful, no such information was available in the sources consulted here.
I extracted information on body mass from Dunning (2008). Migration distance was estimated as the mean of the northernmost and southernmost latitudes during the breeding season minus the mean of the northernmost and southernmost latitudes during winter relying on Cramp and Perrins (1977-1994) and Poole et al. (1993-2002). I also used northernmost and southernmost latitudes during the breeding season and northernmost and southernmost latitudes during winter to test for possible latitudinal effects. These tests were restricted to North American species to avoid problems of differences in latitudinal effects on climate among continents. The species investigated here generally molt in late summer-early fall (Cramp and Perrins 1977-1994; Poole et al. 1993-2002). Therefore, I related the total number of feathers to time since molt estimated as the number of months since August. All data are reported in Additional file 1: Table S1.
Statistical analyses
I log10-transformed body mass, total number of feathers, mass of all feathers, mean mass of feathers and migration distance to achieve normally distributed frequency distributions.
I analyzed allometric relationships between the total mass of all feathers, the total number of feathers and the mean mass of feathers, respectively, in relation to body mass using log10-transformed variables while including species as a random effect to account for differences in sample size among species. I tested whether the allometric relationships were isometric or negative or positive allometric by testing with t-tests whether allometry coefficients differed significantly from unity.
I developed general linear mixed models with species as a random effect thereby controlling for differences in sample size among species while body mass, time since molt and migration distance were fixed factors. Both a linear and a quadratic effect of time since molt were entered into the models to account for non-linear effects of relative time. Furthermore, I included sex and northernmost and southernmost breeding and wintering latitude in these general linear mixed models with species as a random effect thereby controlling for differences in sample size among species while body mass, time since molt and migration distance were fixed factors. Finally, I tested for phylogenetic effects in a general linear mixed model with species and genus as random effects controlling for differences in sample size among species while body mass, time since molt and migration distance were fixed factors. A phylogenetic effect would imply a significant effect of genus. All analyses were made with JMP (SAS 2012).
Results
A total of 91% of the variance in the number of feathers was due to differences among species with the remaining 9% of the variance occurring within species (F=9.42, d.f. = 84, 75, r2=0.91, p < 0.0001). The allometric relationships for the number of feathers, the mass of the plumage and the mean mass of feathers are reported in Table 1. The total mass of all feathers increased isometrically with body mass since the allometry coefficient did not differ significantly from one (t=0.77, d.f. = 74.46, p=0.45). The total number of feathers showed negative allometry (Figure 1A), with an allometry coefficient less than one (t=24.47, d.f. = 85.64, p < 0.001). The average mass of individual feathers likewise increased with body mass showing negative allometry (Figure 1B; Table 2), and the allometry coefficient was less than one (t=5.27, d.f. = 73.1, p < 0.001).
Table
1.
Allometry of mass of all feathers, number of feathers, and mean mass per feather
Variable
F
d.f.
p
Estimate
SE
Log mass of all feathers
516.80
1, 74.46
< 0.0001
0.972
0.043
Log no. feathers
165.02
1, 89.46
< 0.0001
0.266
0.030
Log mean mass of individual feathers
305.24
1, 73.1
< 0.0001
0.768
0.044
The random effect of species for log mass of feathers was 0.0034, 95% CI=-0.0002, 0.0070 accounting for 24% of the variance. The random effect of species for log number of feathers was 0.0047, 95% CI=0.0021, 0.0073 accounting for 55% of the variance. The random effect of species for log mass of each feather was 0.0039, 95% CI=-0.00007, 0.0078 accounting for 26% of the variance.
Figure
1.
(A) The number of feathers in different birds in relation to body mass (g), and (B) the mean mass of feathers in different birds in relation to body mass (g).
The relationship between the number of feathers, total mass of feathers and mean mass of feathers and log migration distance was significantly negative for number of feathers, but not for mass of feathers or mean mass of feathers (no. feathers: F=8.60, d.f. = 1, 81, p=0.044, estimate (SE)=-0.075 (0.026); mass of feathers: F=0.00, d.f. = 1, 60.74, p=0.98; mean mass of feathers: F=0.14, d.f. = 1, 60.67, p=0.71). Thus species that migrated longer distances had fewer feathers for a given body size. The total number of feathers was significantly related to time since molt and time since molt squared (Table 2). This implies that the number of feathers reached a peak halfway through the year after molt (Figure 2). In addition there was a significant effect of body mass with more feathers in larger species (Table 2).
Figure
2.
Total number of feathers in relation to time (months since August) in different birds. Note the curvilinear relationship.
The predicted number of feathers at the end of the molting period from the model in Table 2 was 1259, increasing to 1950 half a year later (a rate of increase by 3.8 feathers per day), and subsequently falling to 1350 by the start of the molting period 12 months later (a rate of loss of 3.3 feathers per day).
There was no significant effect of sex in the analysis presented in Table 2 (F=0.42, d.f. = 1, 142, p=0.52). Furthermore, there were no significant effects of northernmost or southernmost latitude during breeding or during winter (breeding northern latitude: F=1.07, d.f. = 1, 63.33, p=0.30; breeding southern latitude: F=1.49, d.f. = 1, 84.81, p=0.23; winter northern latitude: F=0.22, d.f. = 1, 68.87, p=0.64; winter southern latitude: F=0.29, d.f. = 1, 87.44, p=0.59). Finally, there was no effect of genus on the number of feathers in a mixed model (variance ratio=0.088, 95% confidence intervals -0.00038, 0.00066, percentage variance explained=6.23).
Discussion
The number of feathers showed negative allometry while the mass of feathers showed isometry. The number of feathers showed a hump-shaped relationship with time since molt in August, first showing an increase during fall and winter followed by a decrease during spring and summer. This pattern could be explained as a consequence of selection against feather loss during fall and winter followed by a steady loss during spring and summer. Here I have only analyzed patterns of abundance of feathers and feather loss in a sample of mainly passerine and related birds. Thus the results provided here do not necessarily apply to other orders of birds.
Feathers play an important role in thermoregulation. Here I have shown that the total mass of feathers increased isometrically with body mass. In contrast, the total number of feathers and the mean mass of feathers showed negative allometry implying that small species have relatively more and light feathers. These latter patterns are consistent with expectations from the higher surface to volume ratio of smaller species. Furthermore, they suggest that smaller species have relatively many small feathers.
I did not find a linear decline in the number of feathers from the molting period onwards, raising questions about gain and loss of feathers. Feathers emerge during the annual (or bi-annual) molt, and once the molting period is finished, there is little or no feather growth with the exception of feathers being replaced if completely lost. Such replacement is used as a research tool in studies of ptilochronology (Grubb 2006). An alternative explanation for an increase in the number of feathers during fall and winter is that birds grow more feathers during fall and winter although there is no empirical evidence for such seasonal growth. Hence there appears to be no means by which the number of feathers can increase during fall and winter unless individuals that have already lost feathers are selected against. Here, I have indirectly shown selection for individuals with a larger number of feathers in fall because the number of feathers increased with time during fall, followed by gradual loss of feathers in spring as the importance of thermoregulation diminished when ambient temperatures increased. There was a negative association between the number of feathers and migration distance, while there was no significant relationship between the mass of feathers and the mean mass of individual feathers, respectively, and migration distance. Thus migrants had fewer feathers than residents as expected if the cost of thermoregulation is higher in resident species at higher latitudes. In contrast, there were no significant associations between the number of feathers and northernmost or southernmost latitudinal range during breeding or winter. Gradual loss of feathers in spring and summer when ambient temperatures increase allows for the maintenance of high body temperature in the face of normal activity. Such feathers lost during spring and summer may be used as nest material and provide efficient insulation for developing embryos and nestlings.
The present study raises a number of perspectives for the future. First, are the patterns in non-passerines similar to what has been described here? Second, do tropical species have fewer feathers than temperate species as a consequence of their higher ambient temperature? Third, is feather loss and number of feathers related to susceptibility to predation? Fourth, what is the mechanism that maintains the balance between difficulty of loss of feathers to maintain flying ability and insulation and ease of loss when attacked by a predator? Finally, how does this balance change as feathers become worn and lost prior to molt?
Conclusion
Larger species of birds have more and heavier feathers, and these feathers are lost at a rate that indicates selection against feather loss in fall and winter, while the rate of feather loss remains constant during spring and summer with the number of feathers reaching its lowest level in summer just before the start of molt.
Additional file
Additional file 1: Table S1. Species, genus, migration distance (° latitude), month, sex, number of feathers, mass of feathers (g), body mass (g), number of months after molt, northernmost breeding latitude, southernmost breeding latitude, northernmost winter latitude, and southernmost winter latitude in different species of birds. See Methods for further details.
Competing interests
The author declares that he has no competing interests.
Alström P, Davidson P, Duckworth J, Eames JC, Le TT, Nguyen CU, Olsson U, Robson C, Timmins R. Description of a new species of Phylloscopus warbler from Vietnam and Laos. Ibis. 2010;152:145-68.
Brawn JD, Angehr G, Davros N, Robinson WD, Styrsky JN, Tarwater CE. Sources of variation in the nesting success of understory tropical birds. J Avian Biol. 2011;42:61-8.
Chen T, Meng Y, Jiang A. Distribution and population of Oriental Pied Hornbill in Nonggang Nature Reserve. J Guangxi Agric Biol Sci. 2007;26:20-3 (in Chinese).
Clements R, Sodhi NS, Schilthuizen M, Ng PK. Limestone karsts of Southeast Asia: imperiled arks of biodiversity. Bioscience. 2006;56:733-42.
Collar NJ, Robson C. Family Timaliidae (babblers). In: Del Hoyo J, Eilliott A, Christie DA, editors. Handbook of the birds of the world. Vol. 2. Picathartes to tits and chickadees. Barcelona: Lynx Edicions; 2007. p. 70-291.
Cox WA, Thompson FR Ⅲ, Reidy JL. The effects of temperature on nest predation by mammals, birds, and snakes. Auk. 2013;130:784-90.
Day M, Urich P. An assessment of protected karst landscapes in Southeast Asia. J Cave Karst Stud. 2000;27:61-70.
Du Plessis MA, Siegfried WR, Armstrong AJ. Ecological and life-history correlates of cooperative breeding in South African birds. Oecologia. 1995;102:180-8.
Ford HA. Nest site selection and breeding success in large Australian honeyeaters: are there benefits from being different? Emu. 1999;99:91-9.
Fu Y, Chen B, Dowell SD, Zhang Z. Nest predators, nest-site selection and nest success of the Emei Shan Liocichla (Liocichla omeiensis), a vulnerable babbler endemic to southwestern China. Avian Res. 2017;7:18.
Gill F, Donsker D. IOC World Bird List (v 7.2). 2017. doi: .
Hoyt DF. Practical methods of estimating volume and fresh weight of bird eggs. Auk. 1979;96:73-7.
Ibáñez-Álamo JD, Sanllorente O, Soler M. The impact of researcher disturbance on nest predation rates: a meta-analysis. Ibis. 2012;154:5-14.
Intachat J, Holloway JD, Staines H. Effects of weather and phenology on the abundance and diversity of geometroid moths in a natural Malaysian tropical rain forest. J Trop Ecol. 2001;17:411-29.
Jia C, Sun Y, Swenson JE. Unusual incubation behavior and embryonic tolerance of hypothermia by the blood pheasant (Ithaginis cruentus). Auk. 2010;127:926-31.
Jiang A, Jiang D, Goodale E, Wen Y. Nest predation on birds that nest in rock cavities in a tropical limestone forest of southern China. Glob Ecol Conserv. 2017;10:154-8.
Jiang A, Zhou F, Wu Y, Liu N. First breeding records of Nonggang Babbler (Stachyris nonggangensis) in a limestone area in southern China. Wilson J Ornithol. 2013a;125:609-15.
Jiang A, Zhou F, Liu N. Significant recent ornithological records from the limestone area of south-west Guangxi, south China, 2004-2012. Forktail. 2014;30:10-7.
Jiang D, Nong Z, Jiang A, Luo X. Breeding ecology and nest site selection of Red-whiskered Bulbul (Pycnonotus jocosus) in limestone area, northern tropical region of China. Chin J Zool. 2015;50:359-65 (in Chinese).
Jiang D, Zhou F, Chen T, Jiang A. Breeding notes on 18 bird species in limestone area of Southwestern Guangxi. Chin J Zool. 2013b;48:597-604 (in Chinese).
Lack D. The significance of clutch-size. Ibis. 1947;89:302-52.
Lack D. The natural regulation of animal numbers. Oxford: Clarendon Press; 1954.
Lu Z, Yang G, Shu X, Yu G, Zhou F. Spatial niches of Nonggang Babbler and Streaked Wren Babbler in winter. J Guangxi Norm Univ (Nat Sci Ed). 2015;33(4):120-6 (in Chinese).
Lu Z, Yang G, Zhao D, Wu Y, Meng Y, Zhou F. Guild structure of forest breeding bird community in Nonggang Nature Reserve of Guangxi. Zool Res. 2013;34:601-9 (in Chinese).
Luo Z, Tang S, Jiang Z, Chen J, Fang H, Li C. Conservation of terrestrial vertebrates in a global hotspot of karst area in Southwestern China. Sci Rep. 2016;6:25717. doi: .
MacKinnon J, Phillipps K, He F. A field guide to the birds of China. Oxford: Oxford University Press; 2000.
Mkongewa VJ, Newmark WD, Stanley TR. Breeding biology of an Afrotropical forest understory bird community in northeastern Tanzania. Wilson J Ornithol. 2013;125:260-7.
Morton ES. Nest predation affecting the breeding season of the clay-colored Robin, a tropical song bird. Science. 1971;171:920-1.
Robson C. New Holland field guide to the birds of South-East Asia: Thailand, Peninsular Malaysia, Singapore, Vietnam, Cambodia, Laos, Myanmar. London: New Holland; 2005.
Sanz JJ, Arriero E, Moreno J, Merino S. Female hematozoan infection reduces hatching success but not fledging success in pied flycatchers Ficedula hypoleuca. Auk. 2001;118:750-5.
Shu Z, Zhao T, Huang Q. Vegetation survey in Nonggang Nature Reserve. Guangxi Bot. 1988;Suppl: 185-214 (in Chinese).
Sodhi NS. The effects of food-supply on Southeast Asian forest birds. Ornithol Sci. 2002;1:89-93.
Stutchbury BJ, Morton ES. Behavioral ecology of tropical birds. San Diego: Academic Press; 2001.
Styrsky JN, Brawn JD, Robinson SK. Juvenile mortality increases with clutch size in a neotropical bird. Ecology. 2005;86:3238-44.
Vetter D, Rücker G, Storch I. A meta-analysis of tropical forest edge effects on bird nest predation risk: edge effects in avian nest predation. Biol Conserv. 2013;159:382-95.
Wells DR. The birds of the Thai-Malay Peninsula. Volume 2. The passerines. London: Christopher Helm; 2007.
Wikelski M, Hau M, Robinson WD, Wingfield JC. Reproductive seasonality of seven neotropical passerine species. Condor. 2003;105:683-95.
Woxvold IA, Duckworth JW, Timmins RJ. An unusual new bulbul (Passeriformes: Pycnonotidae) from the limestone karst of Lao PDR. Forktail. 2009;25:1-12.
Yang L, Yang X. Avifauna in Yunnan. Passeriformes. Kunming: Yunnan Science and Technology Press; 2004 (in Chinese).
Zheng Z, Long Z, Zheng B. Fauna Sinica, Aves, Vol. 11: Passeriformes, Muscicapidae, Ⅱ. Timaliinae. Beijing: Science Press; 1987 (in Chinese).
Zhou F, Jiang A. A new species of babbler (Timaliidae: Stachyris) from the Sino-Vietnamese border region of China. Auk. 2008;125:420-4.
Manchiryala Ravikanth, Aamer Sohel Khan, Selvarasu Sathishkumar, et al. Breeding success of long-billed vulture (Gyps indicus) and its drivers in Deccan Plateau, India. European Journal of Wildlife Research, 2025, 71(2)
DOI:10.1007/s10344-025-01909-4
2.
Zu K. Luo, Xian H. Shao, Yu B. Liu, et al. Multiscale nest-site selection and breeding biology: infrared camera monitoring of the great crested grebe Podiceps cristatus in a plateau freshwater lake in southwestern China. Ornithology Research, 2024, 32(3): 197.
DOI:10.1007/s43388-024-00185-1
3.
Li Zhang, Zhenyun Liu, Keping Sun, et al. Multi‐dimensional niche differentiation of two sympatric breeding secondary cave‐nesting birds in Northeast China using DNA metabarcoding. Ecology and Evolution, 2024, 14(7)
DOI:10.1002/ece3.11709
4.
Giovanna Sandretti-Silva, Leandro Corrêa, Mariana Amirati, et al. The win-stay, lose-switch renesting strategy of a territorial bird endemic to subtropical salt marshes. Frontiers in Ecology and Evolution, 2024, 12
DOI:10.3389/fevo.2024.1497317
5.
Xiaocai Tan, Peihao Yan, Zongyue Liu, et al. Demographics, behaviours, and preferences of birdwatchers and their implications for avitourism and avian conservation: A case study of birding in Nonggang, Southern China. Global Ecology and Conservation, 2023, 46: e02552.
DOI:10.1016/j.gecco.2023.e02552
6.
Xiaodong Rao, Jialing Li, Binbin He, et al. Nesting success and potential nest predators of the red Junglefowl (Gallus gallus jabouillei) based on camera traps and artificial nest experiments. Frontiers in Ecology and Evolution, 2023, 11
DOI:10.3389/fevo.2023.1127139
7.
Xiaocai Tan, Shilong Liu, Eben Goodale, et al. Does bird photography affect nest predation and feeding frequency?. Avian Research, 2022, 13: 100036.
DOI:10.1016/j.avrs.2022.100036
8.
Shilong Liu, Qiao Xie, Aiwu Jiang, et al. Investigating how different classes of nest predators respond to the playback of the begging calls of nestling birds. Avian Research, 2022, 13: 100044.
DOI:10.1016/j.avrs.2022.100044
9.
Ma Laikun, Yang Canchao, Liang Wei. Nest-Site Choice and Breeding Success among Four Sympatric Species of Passerine Birds in a Reedbed-Dominated Wetland. Journal of Resources and Ecology, 2021, 12(1)
DOI:10.5814/j.issn.1674-764x.2021.01.003
10.
Morgan C. Slevin, Enroe E. Bin Soudi, Thomas E. Martin. Breeding biology of the Mountain Wren-Babbler ( Gypsophila crassus ). The Wilson Journal of Ornithology, 2020, 132(1): 124.
DOI:10.1676/1559-4491-132.1.124
11.
Laikun Ma, Jianwei Zhang, Jianping Liu, et al. Adaptation or ecological trap? Altered nest-site selection by Reed Parrotbills after an extreme flood. Avian Research, 2019, 10(1)
DOI:10.1186/s40657-019-0141-1
12.
Tonleu Jean, Serge Bobo Kadiri, Ducelier Djoumessi Wamba, et al. Understorey birds nests predation in afrotropical forest ecosystem: A case study of Korup area, Cameroon. Journal of Ecology and The Natural Environment, 2018, 10(8): 192.
DOI:10.5897/JENE2018.0707
Table
1.
Allometry of mass of all feathers, number of feathers, and mean mass per feather
Variable
F
d.f.
p
Estimate
SE
Log mass of all feathers
516.80
1, 74.46
< 0.0001
0.972
0.043
Log no. feathers
165.02
1, 89.46
< 0.0001
0.266
0.030
Log mean mass of individual feathers
305.24
1, 73.1
< 0.0001
0.768
0.044
The random effect of species for log mass of feathers was 0.0034, 95% CI=-0.0002, 0.0070 accounting for 24% of the variance. The random effect of species for log number of feathers was 0.0047, 95% CI=0.0021, 0.0073 accounting for 55% of the variance. The random effect of species for log mass of each feather was 0.0039, 95% CI=-0.00007, 0.0078 accounting for 26% of the variance.
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