A review of Baya Weaver Ploceus philippinus (Linnaeus, 1766) (Aves: Passeriformes: Ploceidae): ecological and conservation status

: Baya Weaver Ploceus philippinus is a highly social and gregarious bird of the family Ploceidae that has been recently listed as ‘Least Concern’ by the IUCN Red List of Threatened Species. In India, four species of genus Ploceus are reported to date. This study focused on the appearance, distribution, diet specificity, nesting ecology, mating behaviour, and physiological responses to seasonal changes of P. philippinus . Populations have declined due to poor cultivation practices by farmers, rapid urbanization, and industrialization that have resulted in habitat loss. Weaver birds also face threats due to natural predators such as birds, and from insect damage to chicks, eggs, and nests.


INTRODUCTION
Baya Weaver Ploceus philippinus is a docile, intelligent, and gregarious sparrow-sized bird that is popularly known for excellent nest-weaving skills (Quader 2006).In 1760, the French zoologist Mathurin Jacques Brisson included a description of the Baya Weaver in his book of ornithology that was based on a specimen that he believed had been collected in the Philippines.Linnaeus (1766) provided a brief description of the Baya Weaver, citing the elongated description of Brisson, and repeated the locality as the Philippines.More than a century later, Hartert (1902) realized that the Baya Weaver does not occur in the Philippines and suggested the type locality should be Ceylon (Sri Lanka).This species is now placed in the genus Ploceus that was introduced by the French naturalist Georges Cuvier in 1816.India is home to four Ploceus (Lack 1954(Lack , 1968;;Grewal et al. 2016;Grimmett et al. 2016): Blackbreasted Weaver P. benghalensis, Streaked Weaver P. manyar, Finn's Weaver P. megarhynchus, and Baya Weaver P. philippinus.There are many works on nesting and population ecology (Quader 2005(Quader , 2006;;Borges et al. 2002;Raju 2009;Pandian & Ahimas 2018;Kumar et al. 2018;Pandian 2022), but a combined review has not been prepared to date.This review provides baseline information about the nesting, mating, and population ecology, in addition to conservation status.

MATERIAL AND METHODS
Available literature was scrutinised for the ecological and conservation studies of Baya Weaver P. philippinus.Old articles were obtained from the Biodiversity Library and open source/online publications.References were collected from various institute libraries and recognised web-based literature.For the present study, 78 articles and books were screened for Baya Weaver studies including aspects such as nesting, mating, population ecology, and conservation status.

Appearance
Female and nonbreeding male: A male and female looks similar in nonbreeding season males exhibit brighter and more vibrant colours during the breeding season (Inskipp et al. 2011).The non-breeding male Baya Weaver boasts a yellow head cap, adorned with fine darker shaft streaks, while its mantle feathers exhibit a central brown hue complemented by distinct yellow margins.The tail and wings are dark brown with lighter margins.On the tertials, margins of the outer vanes are buffy to rusty while they are yellow-olive on the secondaries forming an unobtrusive wing panel.The throat is light brown, the breast yellow and the belly is light yellowish to whitish while the flanks are rather buffy.In addition, tarsi and toes are horn-coloured (Stiels & Schidelko 2013).
Breeding male: The males assumed bright golden yellow plumage on the crown, nape, breast, and sides of the neck.The bill was pale yellow in the non-breeding season but turned blackish in April and became black between May and October (Narasimhacharya et al. 1988).
Food preference: P. philippinus feeds on wider varieties of herbs as annotated in the Table 1.These birds forage in flocks for grains in cultivated fields and sometimes this bird is considered an agricultural pest (Sengupta 1974;Kale et al. 2014) but, in contrast, they also feed on different insects which are causing damage to the cultivated crops (Arigela et al. 2021).

Nesting ecology of P. philippinus
Nest construction pattern and its stages: The Baya Weaver P. philippinus, has been considered an architectural genius for the delicate craftsmanship of building intricate pendant nests.The nest of P. philippinus is pendulous, suspended to leaf tips, monostoried, stalked, and retort shaped with a central nesting chamber and long vertical tube that leads to a side entrance to the chamber (Venkataramani 1981).Wood (1926) mentioned that weaver birds instead of building a nest once or twice in a year they reuse the old nest by repairing it, Raju (2009) reported that male Weaver birds constructed a new nest because of old ones may fall along with the leaf during an annual leaf fall.The Weaver bird rarely constructs a stalk-less nest because such nests are hardly ever excepted by the female weaver bird (Sharma 1995).There are five stages in the construction of a nest initial attachment, roof and egg/brood chamber, antechamber, entrance, and entrance tube (Raju 2009).Nest building was initiated by winding strands of grass around a selected twig until  firm support was secured.A bunch of strands was then woven to form a 'wad' which was further expanded into an initial ring.The initial ring was then built up to form a helmet-shaped nest.Gradually, an egg chamber was added to the helmet and, at this stage, the bird's nest-building activity slowed down.Nest building only continued if the partially completed nest was accepted by the female weaver bird, Once the nest was accepted, a long entrance tube was added marking the completion of nest construction (Narasimhacharya et al. 1987).

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Nest building material: The nest-building material used by this bird may vary according to the locality in India.Most often they use herbs of the family Poaceae as a nest-building material (Table 2).Baya weaver also preferred to build nests close to the power cable, roads and human dwellings (Pandian 2022).
Nest orientation: Borges et al. (2002) reported that the orientation of most of the nests is towards the east, while very few nests are oriented towards the south and north direction and no single nest oriented to west direction.Mean nest-entrance orientation was generally opposite to wind direction so as to be least affected by the south-west monsoon wind (Davis 1971;Pandian 2021a).It was reported that 40% of nest colonies in Rajasthan (Sharma 1990) and 89% of nests in Tindivanam taluka (Pandian & Ahimas 2018), 70% nests towards the east in Villupuram district and 81% of nests in Arakkonam taluka, Tamil Nadu (Pandian 2022) were oriented towards the east probably to protect their nests from the battering south-west monsoon winds.
Nesting platforms: In India, there is a wide variety of plants available to serve the purpose of nesting platforms for the P. philippinus (Ali & Ambedkar 1957;Ambedkar 1958).Availability of nesting materials, surrounding biological environment, temperature, light intensity, humidity, etc., restrict the nest selection of birds (Asokan et al. 2008).Psychic factor such as photoperiodic sensitivity also influence the nest site selection (Welty 1982).A regional bias seems to exist in the choice of certain plant species for nesting by the weaver bird, one of the reasons proposed for such a choice is the protection against intruders provided by the different plant species (Borges et al. 2002).A taking priority over the availability of food and nesting fibres has considered as a primitive factor for selection of nesting site.(Davis 1974).The nesting sites in the fields were always located near a water supply such as irrigation wells, rivers, lakes, ponds, and sewage stagnant water, and in urban areas underneath shady trees (Kumar et al. 2018;Pandian 2022).The apparent bias in the selection of plant species observed in various regions of the subcontinent raises the question of whether this reflects a genuine preference or is simply a consequence of their widespread occurrence in the region.The bird's selection criteria for nesting plants may involve choosing those with tall, sturdy, unbranched trunks, and a crown of swaying fronds.This choice not only provides protection against intruders, rain, and wind but also serves as a means of seeking attention from female weaver birds (Davis 1974).Among the various preferred nesting platforms (Table 3), some of them are also used for roosting and foraging.These birds move in flock to the sugarcane crops and Prosopis juliflora for roosting and foraging purposes (Pandian 2021b).

Mating Behaviour
Mate and nest choice: In many species of weaverbirds, males display their nests to females, suggesting that females may use nests for mate choice (Quader 2005).After the completion of the nest up to the wad stage, females arrive and visit several nests before pairing.Female choice of mates has been presumed to be based largely on the color; material and quality of the available nest (Collias & Collias 1964b, 1984;Crook 1960;Narasimhacharya et al. 1987).Female choice of the site may be influenced by both wind direction and safety from predation (Quader 2003).Most helmets were never made into complete nests and hence nest completion is a good indicator of female choice (Quader 2006).Ambedkar (1964) and Crook (1964) reported that the nest at a higher height is safer from predation than lower-heightened nests.Nest height is believed to be an important influence on nesting success in birds (Martin 1993) within tree nesting species, predation tends to decrease with height (Cresswell 1997; Schmidt & Whelan 1999).Both males and females are polygamous.Males usually build partial nests and complete them only after courting females (Ali et al. 1956).The male may build another helmet to attract another female.If a helmet is not accepted by any female the male often tears it down and builds a new one in its place (Abdar 2013).Quader (2006) found that several aspects of nest location (tree type, diameter of branch, nest height) and nest architecture (fibre thickness) predict direct benefit to females when nesting date and year are statistically controlled.
Breeding season: The Baya Weaver breeds during the rainy season (monsoon) in the Indian subcontinent (Ali & Ripley 1987).The breeding period of the Baya Weaver is largely based on seasonal changes and the availability of the diet.Food availability is preferably dependent on environmental factors such as temperature and rainfall and its ultimate cause to control seasonal breeding (Baker 1938;Immelmann 1971).
Physiological Responses to seasonal changes: The reproductive activity stimulates responses to the photoperiod (Thapliyal & Saxena 1964;Singh & Chandola 1981) as increasing day length during the pre-monsoon season.The stimulation of gonadotropic hormones in P. phillipinus such as leutinizing hormone (LH) and testosterone level varies in response to day length (Thapliyal & Saxena 1964;Stokkan & Sharp 1980) J TT as its concentration increases during the month of April and May and highest between June and September (Narasimhacharya et al. 1987).The expression of gonadotropin inhibiting hormone is high on short days when the duration of nocturnal melatonin is increased, and low on long days when the duration of nocturnal melatonin is decreased (Ubuka et al. 2005).The environmental factors also contributed to the ecological significance via accompanying pre-breeding sexual changes and behaviour (Morley 1943;Sharp et al. 1986).A pre-nuptial molt occurred between March and June and a post-nuptial molt between October and November (Narasimhacharya et al. 1987).The lightning of the bill color starts to cause in August and its turns to a complete straw color in November and depigmented their plumage to the non-breeding type (Rani et al. 2007;Pandey & Bhardwaj 2015).The alteration in night light as a bright light during the night alters the resting pattern

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of this bird it induced a fragmented activity in the early phase of night and enhancement at late night instead of the actual onset of the day (Raap et al. 2015;Touitou et al. 2017;Kumar et al. 2018).The midnight activity increases in presence of bright light due to advancement in the endogenous clock function as the suppression level of melatonin and increased body temperature (Kumar et al. 2002;Jong et al. 2015;Kumar et al. 2018).
An endogenous clock system sensitive to light enables the bird to synchronize its physiological activities at the appropriate time of the day and time of the year (Kumar & Follett 1993a;Kumar et al. 1996).

Threats
Pandian (2021b) reported that farmers are the prime reason behind the declining population of the Ploceus philippinus in India.They burn herbs and shrubs under nest supporting trees and by clearing grasses around irrigation wells which may cause the scarcity of the nesting substrata for the P. philippinus.Individuals of Rufous treepie damage the nest of the weaver birds by driving a circular hole over the nest and predating the egg and chicks and it is also damaged by other bird species such as Corvus splendens, Corvus macrorhynchos, Dicrurus macrocercus, and Eudynamys scolopaceus (Ali 1931;Pandian 2021aPandian , 2022)).Ali et al. (1957) observed that the predation by House Crow Corvus splendens (Passeriformes: Corvidae) is very common.Pandian (2022) reported that 1,050 nests had fallen during their study period among various sites in Tamil Nadu, it has been found that total of 25 eggs and 18 dead chicks were spread near fallen nests may due to various biotic and abiotic factors as suggested by Ali et al. (1957), Collias & Collias (1959, 1962), and Pandian (2021b).Rapid urbanization and industrialization have resulted in declining areas of cultivation up to 20%, particularly cereal crops, thus causing lack of food grains and insect fauna to P. philippinus (Pandian 2018).The presence of heavy metal contamination in excreta has indicated that it might have a negative impact on the abundance of Baya Weaver in Punjab state (Sidhu & Kler 2021).Ploceus philippinus has most recently been assessed for The IUCN Red List of Threatened Species in 2016 as 'Least Concern' (Birdlife International 2016).

CONCLUSION
This study provides information about appearance, food specificity, nesting ecology, and mating behaviour of the P. philippinus.It is found that a small sparrow sized weaver bird shows sexual dimorphism in appearance.They mostly prefer a wider variety of herbs species in their diet as it perennially found during all seasons but highly flourish during cold season.Along with the food availability some physiological changes bring a seasonal breeding bird.These birds are famous for their nest weaving practices, it can be considered as a nidificate architect.Species specific studies and detailed knowledge of local bird population can greatly help in effective management measures, as several scientific aspects covered by the many initiators among diverse countries.It can help to bridge gaps in knowledge and benefit the future survival of a population of P.