Savanna Nightjar Research Articles

Savanna Nightjars (Caprimulgus affinis stictomus) adjust calling height to gain amplitude advantage in urban environments

Savanna Nightjars (Caprimulgus affinis stictomus) adjust calling height to gain amplitude advantage in urban environments

Taxonomic revision of the Savanna Nightjar (Caprimulgus affinis) complex based on vocalizations reveals three species

BackgroundThe Savanna Nightjar (Caprimulgus affinis) is a widespread, polytypic species which was previously treated as two or three species. It is currently treated as a single species based on superficial similarity of their songs but no detailed comparisons of the songs in this complex have been made.MethodsA total of 15 acoustic variables were measured for the songs of 86 individuals representing 8 of the 10 subspecies in the complex.ResultsThree major groups can be distinguished based on univariate and multivariate analyses: a northern group consisting of the subspecies C. a. monticolus, C. a. amoyensis and C. a. stictomus; a southern group consisting of C. a. affinis, C. a. kasuidori, C. a. timorensis and C. a. propinquus; and a third group in the Philippines consisting of C. a. griseatus.ConclusionsIt is here argued that these groups are best treated as species, and that Franklin’s Nightjar (C. monticolus) and Kayumanggi Nightjar (C. griseatus) are reinstated as separate species.

Biometrics, distribution, and breeding notes of Savanna Nightjar (Caprimulgus affinis) in several islands of Indonesia

Abstract. Widodo W, Sulistyadi E. 2021. Biometrics, distribution, and breeding notes of Savanna Nightjar (Caprimulgus affinis) in several islands of Indonesia. Biodiversitas 22: 2756-2762. The Savanna Nightjar Caprimulgus affinis Horsfield, 1821, a member of the family Caprimulgidae, is a sexually dimorphic, insectivorous nightjar species commonly found in Southeast Asia, including Indonesia. A least-concern species, Savanna Nightjar has diverse habitats from grasslands to shrubs to high-rise rooftops in the middle of the city. Yet, its breeding habits, particularly in urban areas, remain obscure. The purpose of the research is to discuss the biometric measurement, distribution pattern and notes of the breeding of Savanna Nightjar, through analyzing 50 specimens originating from Java, Sumatra, Billiton, Borneo, and Nusa Tenggara Islands belonging to the Museum of Zoology Bogor (MZB) in Cibinong and through a series of observation. The morphological measurements of specimens include the measurements of the length of the bodies, the wings, the tails, the bills, and the tarsi. One-way ANOVA analysis showed that the length of the body and the tail of Savanna Nightjar in Nusa Tenggara are significantly longer than those of Savanna Nightjar in Java, Sumatra, Billiton, or Borneo islands. The biometric differences could have been contributed to different habitat characteristics. Additionally, it was found the likelihood of breeding habit of Savanna Nightjar in urban areas with that of the countrysides because of the resemblance of semi-natural ecosystems in the city such as artificial rivers, small lakes, and parks to Nightjar’s open landscape natural habitats, which facilitates the breeding habits. Still, the migration of Savanna Nightjar from open country-landscapes to the metropolitan areas remains elusive and requires a more detailed study

Acoustic preadaptation to transmit vocal individuality of savanna nightjars in noisy urban environments

As urbanization has expanded dramatically, the impacts of urban noise on wildlife have drawn increasing attention. However, previous studies have focused primarily on diurnal songbirds and much less on nocturnal nonpasserines such as nightjars. The savanna nightjar has recently successfully colonized urban areas in Taiwan. Using 1925 calls recorded from 67 individuals, we first investigated the individual differences of the acoustic structures; and, for those acoustic variables with significant individual differences, we examined the correlation between the acoustic structures and the ambient noise levels. We then compared the transmission efficacy of vocal individuality among three sets of acoustic variables: all acoustic variables, noise-related variables, and noise-unrelated variables. Using seven artificial frequency-shifted calls to represent seven different individuals in playback-recording experiments, we also investigated the transmission efficacy of vocal individuality and variable accuracy in three different urban noise levels (high, medium, low). We found that all 30 acoustic variables derived from the acoustic structures demonstrated significant individual differences, and 14 frequency-based variables were negatively correlated with ambient noise levels. Although transmission efficacy was significantly affected by urban noise, individuality information was still transmitted with high accuracy. Furthermore, the noise-unrelated structures (which included the maximum frequency, the maximum amplitude frequency, and the mean frequency of the call) had a significantly higher transmission efficacy of vocal individuality than the noise-related variables (which included the minimum frequency, the frequency at the start and the end of the call) in both field observation and playback-recording experiments. We conclude that these noise-unrelated acoustic features may be one of the key preadaptations for this nocturnal nonpasserine to thrive so successfully in its newly adopted urban environment.

Fragmented Riverine Habitats in Taiwan Have Spatio-Temporal Consequences, Re-Distributing Caprimulgus affinis into Urban Areas Leading to a Human–Wildlife Conflict

Caprimulgus affinis is an endemic species commonly known as the Taiwan nighthawk, forest nighthawk, or South Asian nighthawk. In recent years, the C. affinis population has gradually moved outward from river habitats into the metropolitan areas of Taiwan. Because male birds’ booming sounds at night can reach up to 90 dB or higher and they can be intermittently tweeting for more than 10 hours, they often disturb the sleep of urban residents and can even cause nightmares. In this study, we analyzed long-term survey data to assess the distribution history of C. affinis in Taiwan. By using 1738 entries of observation data collected from 1999 to 2014, a model of C. affinis distribution was constructed, and a geostatistical method was used to improve the accuracy of the model estimate. In addition, the Mann–Kendall trend test was applied to predict future C. affinis distribution. Based on the results, four variables were selected to construct the C. affinis distribution matrix. Urban population, coastal proximity, and distance to upstream river location represented positive driving forces, whereas city elevation was a negative driving force. C. affinis is currently distributed on the plains of central and southern Taiwan and in eastern Taiwan. The C. affinis emergence trend diagram was plotted using the time–space trend diagram, which showed yearly increases in the C. affinis populations in urban and settled areas including central, western, northeastern, and southeastern Taiwan and yearly decreases in the populations in rural areas including northern and southern Taiwan, especially in fragmented riverine habitats. Regression kriging can correctly describe the distribution of the entire C. affinis population, which leads to the correct understanding of the biological corridor of C. affinis in their migration through the graphical contours in GIS. The analytic model in this study contributes to the establishment of the time–space trend diagram.

Injury feigning in the Savanna Nightjar: a test of the vulnerability and brood value hypotheses

Nest predation is a major threat to the survival of young birds and is thus a crucial selective pressure influencing the evolution of life history traits. Injury feigning is a nest-defense mechanism in which the parents attract the attention of predators to secure their offspring. Because parents may incur a cost from injury feigning, they should adjust their injury-feigning behavior to different situations to maximize fitness. In this study, we used the Savanna Nightjar, Caprimulgus affinis, as a model organism to test the vulnerability and brood value hypotheses for predicting the occurrence of injury-feigning behavior. A field study was performed between 2006 and 2012, and observations were recorded from 123 nests. Both nestling movement and injury feigning increased after hatching, reached their peak at a nestling age of 8–10 days, and then declined afterward. In addition, the frequency of injury feigning by the female differed between habitats, being higher in a low-plant-cover habitat than in a high-plant-cover habitat. Both findings are consistent with the vulnerability hypothesis. By contrast, the intensity of injury-feigning behavior did not linearly increase with nestling age and brood size; thus, the brood value hypothesis was not supported.

Unusual Congregation of Savanna Nightjar <I>Caprimulgus affinis</I> in a Wheat Field

On February 15, 2012, we were at Partala (22° 49′ 4.56′′ N; 80° 18′ 33.83′′ E), initiating People’s Biodiversity Register. Partala is situated in Narayanganj tehsil of Mandla district in Madhya Pradesh. The village is surrounded by forested hills on three sides, and a small river flows amidst them. The river banks are surrounded by agricultural fields with scattered trees. The main crops are paddy, wheat, maize, and various pulses. The dominant vegetation in this region is Tectona grandis, Terminalia arjuna, Aegle marmelos, Soymida febrifuga, Madhuca indica, Ficus religiosa, and Butea monosperma. At 18:15 hrs we reached a huge Peepal tree Ficus religiosa, which is one of the roosting sites of the Yellowfooted Green-pigeon Treron phoenicoptera. On reaching, we heard a cacophony of nightjar calls from an adjacent field. It was getting dark and we could only see silhouettes of the nightjars flying erratically, crisscrossing each other above the wheat field. There were around 30–35 birds, continuously calling and sallying on swarms of insects (moths). We identified them as Savanna Nightjar Caprimulgus affinis based on their distinct cweetzz, cweetzz, cweetzz calls. Along with nightjars, small insectivorous bats were also observed feasting on the moths. Two more species of nightjars, namely Indian Jungle Nightjar Caprimulgus indicus and Indian Little Nightjar Caprimulgus asiaticus, are found in this region. However, we could not hear the calls of these species to ascertain their presence in the congregation. The nightjars were scattered across the wheat field, and since visibility was extremely poor, we could not take photographs. We observed this congregation for almost half an hour, after which we could not follow their movements due to nightfall. Ali and Ripley (1983) indicate that the Savanna Nightjar forms loose flocks of 7 or 8 while undertaking local movements. Similarly, Rasmussen and Anderton (2005) also state that Savanna Nightjars ‘often fly in groups’. These anecdotes suggest the gregarious tendency of Savanna Nightjars. However, large congregations of Savanna Nightjars, as recorded by us, have not been published. A similar observation was made by P. Jeganathan (pers. comm.) in Sri Lankamalleshwara Sanctuary, Andhra Pradesh, on June 16, 2001. He observed 15 individuals, probably of Indian Little Nightjar Caprimulgus asiaticus, near an agricultural field foraging on insects. The European Nightjar Caprimulgus europaeus is known to form loose parties or flocks of 6 to 20 individuals on their passage to autumn migration (Ali and Ripley 1983). The only known gregarious species of nightjar is the Sand-colored Nighthawk Chordeiles rupestris of South America, with flocks of up to 50 individuals observed (del Hoyo et al. 1999). Del Hoyo et al. (1999) also mention that during migration and in the non-breeding season, more than one species of nightjar join to form groups of more than 20 birds, gathering at good food resources, such as grazing animals, animal corrals, lights or fires, or at insect swarms or termite emergence. Some species of nighthawk, such as Common Nighthawk Chordeiles minor and Lesser Nighthawk Chordeiles acutipennis, often forage in large flocks of several hundred birds. On February 16, 2012, we collected some moths which were identified as Helicoverpa sp., a common pest on wheat. King (1994) mentions that “Adult moths emerge from just after dark to midnight and crawl onto a plant or vertical substrate where their wings dry”. Williams et al. (2011) mentions that “Night birds such as the Tawny Frogmouth and nightjars feed on Helicoverpa moths as they are also active at night.” These probably explain the reason for the large congregation of Savanna Nightjars sighted by us at Partala. It is very likely that such assemblages are common in this region. However, this needs further investigation.

Bird colonization of Anak Krakatau, an emergent volcanic island

Bird colonization of Anak Krakatau in the 1980s serves as a model for the early colonization processes, which were mostly undocumented, that occurred on the archipelago in the first two decades of this century. Anak Krakatau, which emerged from the sea in 1930, also provides an opportunity to study the formation of an avian communityde novo. Thirty-seven species of birds have been recorded since 1951. Shore birds and aerial insectivores were the first species to exploit the newly emerged island. Plant succession, which is proceeding at different rates on different parts of the island, has provided niches for birds to permanently colonize. Species of open habitats (Caprimulgus affinis, Centropus bengalensis) were the first colonists, followed next by ecological generalists with good dispersal ability (Pycnonotus Goiavier, Halcyon chloris) ; the next species were those that exploit casuarina woodland and forest and the most recent wave of colonists have been frugivores that arrived after figs began to bear fruit in 1985. Three raptors that hunt on the island have limited the colonization of three large frugivores. Most, but not all, colonists have come from the older islands, including those species denied open habitats by plant succession. Comparisons are made with the bird colonization of Rakata during the first two decades of this century. Most birds on Anak Krakatau are insectivores and are restricted to two areas of trees some 12 hectares in total. Foraging methods and sites show little overlap, but dietary analysis in August 1986 showed some common prey items. The very high density of insectivores may be a function of insect abundance on the island and high fecundity and tolerance of crowding by early bird colonists.

NESTS AND EGGS OF SOME AFRICAN NIGHTJARS

Summary Colebrook-Robjent, J.F.R. 1984. Nests and eggs of some African nightjars. Ostrich 55: 5–11. Breeding data based on 245 nests found between 1969 and 1983 in one study area in Choma, and on other nests from elsewhere in the Southern Province, Zambia, are presented for four Caprimulgus and one Macrodipteryx species. Nest sites, breeding seasons, clutch size, laying sequence, measurements, weights and descriptions are given and compared for the five common savanna nightjars of south and central Africa. Errors in the literature are revealed.