Grey warbler: Difference between revisions
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{{Short description|Species of bird}} |
{{Short description|Species of bird}} |
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{{Use New Zealand English|date=July 2024}} |
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{{speciesbox |
{{speciesbox |
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| name = Grey warbler |
| name = Grey warbler |
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| genus = Gerygone |
| genus = Gerygone |
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| species = igata |
| species = igata |
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| authority = ([[Jean René Constant Quoy|Quoy]] & [[Joseph Paul Gaimard|Gaimard]], 1832) |
| authority = ([[Jean René Constant Quoy|Quoy]] & [[Joseph Paul Gaimard|Gaimard]], 1832) <ref>Quoy and Gaimard, in Dumont d’Urville, 1832. ''Curruca igata'' (protonym). Voyage de la corvette l'Astrolabe, Zool., 1, p. 201, Atlas, 1833, Oiseaux, pl. 11, fig. 2 [https://www.biodiversitylibrary.org/page/2064257 BHL]</ref> |
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| synonyms = |
| synonyms = * ''Curuca igata'' ([[protonym]]) |
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{{Specieslist |
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|Gerygone flaviventris|Gray 1844 |
|Gerygone flaviventris|Gray 1844 |
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|Gerygone assimilis|Buller 1865 |
|Gerygone assimilis|Buller 1865 |
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The '''grey warbler''' ('''''Gerygone igata'''''), also known by its [[Māori language|Māori]] name '''{{lang|mi|riroriro}}'''<ref>''TPH 7/7/1905 p3 ''http://www.maoridictionary.co.nz/search?idiom=&phrase=&proverb=&loan=&keywords=Riroriro&search=</ref> or outside New Zealand as the '''grey gerygone''', is an [[insectivore|insectivorous]] bird in the family [[Acanthizidae]] [[Endemism|endemic]] to [[New Zealand]] |
The '''grey warbler''' ('''''Gerygone igata'''''), also known by its [[Māori language|Māori]] name '''{{lang|mi|riroriro}}'''<ref>''TPH 7/7/1905 p3 ''http://www.maoridictionary.co.nz/search?idiom=&phrase=&proverb=&loan=&keywords=Riroriro&search=</ref> or outside New Zealand as the '''grey gerygone''', is an [[insectivore|insectivorous]] bird in the family [[Acanthizidae]] [[Endemism|endemic]] to [[New Zealand]]. It is sometimes known as the '''teetotum''' or '''rainbird'''.<ref name="NZBO">{{Cite web |title=Grey warbler {{!}} Riroriro |url=https://www.nzbirdsonline.org.nz/species/grey-warbler |access-date=12 October 2024 |website=New Zealand Birds Online |language=en-NZ}}</ref> Its natural habitat is forests, but also tends to occupy lower vegetation habitats.<ref name=":0">{{Cite book |last=Heather |first=B.D |title=The Field Guide to the Birds of New Zealand |last2=Robertson |first2=H.A. |date=2005 |publisher=Penguin Books |year=2005 |location=Auckland |publication-date=2005 |pages=146, 148, 149, 391, 392 |language=English}}</ref> These insectivorous birds feed on insects living in shrubs, and often feed on the wing.<ref name=":0" /> They are found throughout New Zealand, as well as offshore islands where shrub exists.<ref name=":1">{{Cite book |last=Chambers |first=S |title=Birds of New Zealand - Locality Guide |date=2009 |publisher=Arun Books |year=2009 |edition=3rd |location=Orewa, New Zealand |publication-date=2009 |pages=241-242 |language=English}}</ref> In fact, these birds even flourish in suburban areas, as long as there is vegetation present.<ref name=":1" /> |
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==Description== |
==Description== |
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The grey warbler has a long tail that is darker than its grey-brown body, with white tail end markings as well as a white tail underside.<ref name=":1" /> There is little [[sexual dimorphism]] between males and females, aside from females usually being smaller than males.<ref name=":0" /> Warblers are especially small; weighing around 6.5g with an average length of only around 10cm.<ref name=":0" /> Adults have a signature ruby red eye, while juveniles have a brown eye, as well as yellowish feathers around the face and underbody.<ref name=":0" /> Its nest is especially unique among birds, with a pear shaped, dome like hanging nest that has a circular side entrance hole.<ref name=":0" /> |
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One of the smallest birds found in New Zealand, grey warblers are about 11 centimeters long, with a weight of up to 6.5 grams.<ref name="NZBO" /> It has grey-brown plumage (with a slight olive-green tint), with the face, throat and breast being pale-grey. The abdomen is off-white with a slight yellow tinge. The tail is white underneath and dark brown on top with white tips being visible in flight. They also have a distinctive ruby-red eye. Females are typically smaller than the male, but otherwise there is little sexual dimorphism. The young are paler with no hint of yellow and have brown eyes. |
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=== Song === |
=== Song === |
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The male's song often starts with a series of three squeaks and builds into a distinctive long plaintive wavering trill that rises and falls. Only the male warblers sing year-round, to attract mates and defend [[territory]].<ref name=":2">{{Cite journal |last=Gill |first=Brian J. |date=1982 |title=BREEDING OF THE GREY WARBLER GERYGONE IGATA AT KAIKOURA, NEW ZEALAND |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1474-919X.1982.tb03752.x |journal=Ibis |language=en |volume=124 |issue=2 |pages=123–147 |doi=10.1111/j.1474-919X.1982.tb03752.x |issn=0019-1019}}</ref> Male songs are particularly loud during summer and spring, which lines up with the warblers breeding season.<ref name=":1" /> The warbler’s song is a pleasant, soft warble and varies between different populations.<ref name=":1" /> In fact, studies looking at temporal aspects of warbler song found that the song shifted to a higher frequency over a period of 7 years.<ref name=":3">{{Cite journal |last=Azar |first=Joseph F. |last2=Bell |first2=Ben D. |last3=Borowiec |first3=Marta |date=2014 |title=Temporal change of the song of a local population of the Grey Warbler ( Gerygone igata ): has its song changed over time? |url=https://www.tandfonline.com/doi/full/10.1071/MU13039 |journal=Emu - Austral Ornithology |language=en |volume=114 |issue=1 |pages=80–85 |doi=10.1071/MU13039 |issn=0158-4197}}</ref> It was hypothesised that this was due to the reintroduction of native species to the warbler’s habitat.<ref name=":3" /> The purpose of the song is not only to attract a mate, but also to ward off potential threats that enter a warbler’s territory, whether that be predators or other warblers.<ref name=":0" /> |
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The male's song often starts with a series of three squeaks and builds into a distinctive long plaintive wavering trill that rises and falls. They sing throughout the year but most vigorously when nesting, during spring. Grey warblers are often heard more than they are seen. |
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{{listen|filename=Grey warbler song.ogg|title=Grey warbler recording|description=Territorial call, flying between perches, answering a tape recorder.|pos = left}} |
{{listen|filename=Grey warbler song.ogg|title=Grey warbler recording|description=Territorial call, flying between perches, answering a tape recorder.|pos = left}} |
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==Behaviour== |
==Behaviour== |
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===Feeding=== |
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The grey warbler is a predominantly [[Insectivore|insectivorous]] bird, feeding on organisms such as [[Spider|spiders]], [[Beetle|beetles]], and [[Fly|flies]].<ref name=":0" /> They do this by hovering around shrubs, and picking [[Invertebrate|invertebrates]] off leaves.<ref name=":0" /> However, they have been seen to occasionally eat fruits, perhaps to make up for limiting nutrients that are low in invertebrates, or due to their very high energy method of feeding.<ref name=":0" /> |
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Grey warblers mainly feed upon spiders, insects and their larvae. They are very active, and almost never stay still as they move from one perch to another. |
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=== Breeding === |
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The breeding season in grey warblers is especially long, lasting from August to January.<ref name=":0" /> A breeding pair usually establishes a territory around late July to August, and defends this territory until the end of the breeding season.<ref name=":2" /> Territories are defended by males by chasing away individuals, while also utilising loud, continuous singing.<ref name=":0" /> Females also tend to join in with these chases and tend to have a higher chance of joining the chase if an individual gets too close to the nest.<ref name=":0" /> In terms of mating behaviours, males sing all year around, and this identifies the sex of the warbler as there is no clear sexual dimorphism in the species aside from size.<ref name=":2" /> Males also perform a wing fluttering behaviour, involving rapid flapping of their wings.<ref name=":2" /> This is perhaps an effort to increase the strength of the [[pair bond]] and synchronise with their partners behaviour, as the display occurs throughout all stages of breeding, especially when the female is present.<ref name=":2" /> |
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===Nesting and Parental Care === |
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[[File:Gerygone flaviventris, Gray. Grey Warbler. "Riro-riro.".jpg|thumb|Illustrations of grey warbler nests (1888)]] |
[[File:Gerygone flaviventris, Gray. Grey Warbler. "Riro-riro.".jpg|thumb|Illustrations of grey warbler nests (1888)]] |
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[[File:Juvenile Grey Warbler.JPG|thumb|Juvenile grey warbler]] |
[[File:Juvenile Grey Warbler.JPG|thumb|Juvenile grey warbler]] |
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Grey warblers are unique among New Zealand birds in building a pear-shaped nest with a side entrance near the top. Breeding season in the grey warbler lasts 6 months, from the first building to the last fledging.<ref name=":2" /> Their season starts early, and as a result they often complete building and laying before the last day.<ref name=":2" /> The early start for the season is likely due to parasitism by the [[Shining bronze cuckoo|shining cuckoo]], ''[[Shining bronze cuckoo|Chrysococcyx lucidus]].''<ref name=":1" /> The early start allows the warbler chicks to be out of the nest by the time the cuckoos’ season starts (around September or October), and therefore only the second clutch is impacted.<ref name=":1" /> Grey warblers’ nest in a range of different small-leaved trees and shrubs, especially [[Kunzea ericoides|kānuka]].<ref name=":4">{{Cite journal |last=Gill |first=B.J. |date=1983 |title=Breeding habits of the Grey Warbler (Gerygone igata). |url=https://www.researchgate.net/publication/273134695_Breeding_habits_of_the_grey_warbler_Gerygone_igata |journal=Notornis |volume=30 |issue=2 |pages=137-165}}</ref> Only females gather materials and build the nest, spending from 7-27 days to complete the pear-shaped nest.<ref name=":2" /><ref name=":4" /> Males do, however, accompany the females on trips away from the nest, likely as an act of mate defence.<ref name=":2" /> These nests consist of a range of materials; the outside of the nest is often composed of stout material (for instance rootlets), as well as moss and [[Wool|sheep’s wool]], all bound together using [[Spider web|cobwebs]].<ref name=":4" /> Some of the nests also have a middle layer of wool or clematis seeds.<ref name=":4" /> The variation in nest materials often aligns with what is available in the warbler’s [[home range]].<ref name=":4" /> |
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Grey warblers are unique among New Zealand birds in building a pear-shaped nest with a side entrance near the top. The male collects nesting material, but the female builds the nest from grass, leaves, rootlets and moss, held together with spider web threads, anywhere from 2 to 25 feet above the ground, lined with feathers and other soft material. It is attached to a twig at the top, but is often also secured at the back or sides. The male is not involved in nest building or incubation, but helps to feed nestlings and fledglings. The 3 to 6 eggs, each laid 2 days apart, are pinkish-white with fine reddish-brown speckles all over. The eggs, weighing 1.5 g are about 17 mm long and 12 mm wide. Incubation takes about 19 days and the chicks spend another 15 to 19 days in the nest. |
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After building, female warblers often only delay around 8 days before laying their eggs.<ref name=":2" /> Due to this fast turnover, nests found later in the breeding season are often difficult to find.<ref name=":2" /> Laying of eggs occurs over 15-16 weeks of the year, and the first clutch is laid at different times during a 6-week period.<ref name=":2" /> One clutch is often around 2-5 eggs, and there is at least a 2-day gap between the laying of each egg.<ref name=":0" /> [https://dictionary.cambridge.org/dictionary/english/incubation Incubation] occurs when the last egg is laid, where only the female incubates for a period of 17-21 days.<ref name=":2" /> Once hatched, the young warblers don’t leave the nest for around 17 days, and once they have left the nest are still fed for around 35 days.<ref name=":0" /> Over the whole laying period, the grey warbler only produces two clutches at a slow rate over the long breeding season.<ref name=":2" /> This is likely due to New Zealand’s mild conditions, which results in food not declining over the winter.<ref name=":2" /> Therefore, the warbler’s population size will always be close to the limit set by resource availability, so there is reduced ability for extra breeding due to energy limitations. |
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Their breeding season is from August to January and they usually manage two clutches. The [[shining bronze cuckoo]], a [[brood parasite]], often targets the second clutch.<ref>{{cite book|last=Davies|first=Nick|title=Cuckoos, Cowbirds and Other Cheats|publisher=A&C Black|year=2010|pages=94|isbn=978-1408135860|url=https://books.google.com/books?id=PusIeZgkgMoC&q=%22Shining+Bronze+Cuckoo%22&pg=PA94}}</ref> |
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Both sexes spend time feeding young.<ref name=":4" /> Grey Warblers will feed their young solely with small invertebrates, but traces of grass were seen in the gut of young warblers, likely due to accidental [[ingestion]].<ref name=":4" /> Once food has been delivered to the nest, parents often remove the [[Gelatin|gelatinous]] [[Fecal sac|faecal sacs]] produced by the nestlings, before moving to a perch 15m away from the nest to dispose of the sacs.<ref name=":4" /> |
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=== Begging === |
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In avian species, [[Begging in animals|begging]] behaviour is very common in young [[Hatchling|hatchlings]], to capture the attention of a parent bird to gain access to more food.<ref name=":5">{{Cite journal |last=Anderson |first=Michael G. |last2=Brunton |first2=Dianne H. |last3=Hauber |first3=Mark E. |date=2010 |title=Reliable Information Content and Ontogenetic Shift in Begging Calls of Grey Warbler Nestlings |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1439-0310.2010.01750.x |journal=Ethology |language=en |volume=116 |issue=4 |pages=357–365 |doi=10.1111/j.1439-0310.2010.01750.x |issn=0179-1613}}</ref> Often, the level of begging will differ depending on different factors, for instance hunger level and age.<ref name=":5" /> As with most animal behaviour, there is always a toss-up between the costs and the benefits of the behaviour; in this case, [[predation]] pressure will increase with more begging from young.<ref>{{Cite journal |date=1994-08-22 |title=Experimental evidence that nestling begging behaviour incurs a cost due to nest predation |url=https://royalsocietypublishing.org/doi/10.1098/rspb.1994.0110 |journal=Proceedings of the Royal Society of London. Series B: Biological Sciences |language=en |volume=257 |issue=1349 |pages=161–164 |doi=10.1098/rspb.1994.0110 |issn=0962-8452}}</ref> In other bird species, studies have highlighted the positive correlation between increased begging behaviour and [[predation]] risk, especially for birds nesting at ground level.<ref name=":6">{{Cite journal |last=Gill |first=Brian J. |date=1983 |title=Brood‐parasitism by the Shining Cuckoo Chrysococcyx lucidus at Kaikoura, New Zealand |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1474-919X.1983.tb03082.x |journal=Ibis |language=en |volume=125 |issue=1 |pages=40–55 |doi=10.1111/j.1474-919X.1983.tb03082.x |issn=0019-1019}}</ref> The begging behaviour of the grey warbler is especially unique, with many factors influencing how a parent responds to begging calls in its [[offspring]]. For instance, the adult grey warbler uses specific behaviours to reduce the predation pressure of the hatchlings' begging. Parents can utilise a switch-off signal/call, to communicate with its young when predators are present, and therefore stop the begging of the hatchlings to avoid being located by the predators.<ref name=":7">{{Cite journal |last=Anderson |first=Michael G. |last2=Brunton |first2=Dianne H. |last3=Hauber |first3=Mark E. |date=2010-02-01 |title=Species specificity of grey warbler begging solicitation and alarm calls revealed by nestling responses to playbacks |url=https://linkinghub.elsevier.com/retrieve/pii/S0003347209005223 |journal=Animal Behaviour |volume=79 |issue=2 |pages=401–409 |doi=10.1016/j.anbehav.2009.11.017 |issn=0003-3472}}</ref> This is a feature of a lot of avian species, but studies discovered that after alarm calls, rather than ceasing begging, grey warbler hatchlings would change the structure of their call.<ref name=":7" /> This behaviour functions to reduce the cost of the begging behaviour, by increasing chance of being fed while also decreasing predation pressures.<ref name=":7" /> |
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Grey warbler hatchlings also alter their call depending on hunger and age.<ref name=":5" /> Studies highlighted that as a chick became hungrier, call structure narrowed in [[frequency]] range, while decreasing in [[amplitude]].<ref name=":5" /> Furthermore, as a chick aged, duration decreased, and frequency increased.<ref name=":5" /> These differences in call structure with age and hunger highlight that begging in grey warbler hatchlings is far more complex than just begging for food; the type of call will communicate to the parent what state it is in, and therefore determine the amount of food a chick may receive.<ref name=":5" /> There are also [[Biological interaction|interspecific]] impacts of these specific begging calls. For instance, the brood parasite ''Chrysococcyx lucidus'' (shining cuckoo) [[Parasitism|parasitises]] the grey warbler by laying its eggs into grey warbler nests during the second clutch, resulting in the parent grey warblers having to raise the cuckoo’s young.<ref name=":6" /> This can have major consequences, as cuckoo chicks grow larger than warbler chicks, so often end up pushing the young warblers out of the nest.<ref name=":0" /> For the cuckoo hatchling to survive and be successful, it needs to identically mimic the grey warbler chicks begging behaviour. The complexity of grey warbler begging may mean that the cuckoo will also have to match these highly specific calls.<ref name=":5" /> |
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=== Aggression and territoriality === |
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As mentioned, warblers set up territories just prior to breeding season, and therefore show aggressive behaviours to defend those territories.<ref name=":0" /> Studies indicated that the grey warbler displays very strong territorial behaviours in comparison to other birds.<ref name=":8">{{Cite thesis |last=Cameron |first=Heather B. |date=1990|url=https://ir.canterbury.ac.nz/items/e4f0fd14-e3f4-4d34-8dfe-e43763bd3504 |title=Spacing behaviour, time budgets and territoriality in rifleman (Acanthisitta chloris chloris) and grey warbler (Gerygone igata) at Kowhai Bush |doi=10.26021/8904 |degree=MSc|publisher=[[University of Canterbury]] |access-date=12 October 2024|language=en}}</ref> Males spend a smaller proportion of their time feeding chicks than other birds living in the same [[Niche construction|niche]], and therefore have more time to perform [[Vigilance (behavioural ecology)|vigilance]] and territorial behaviours.<ref name=":8" /> Warbler males also spend a significant amount of time [[mate guarding]]; for instance, when the female is gathering materials to build the nest.<ref name=":8" /> Studies highlighted the aggressive interspecific behaviour grey warblers show towards other bird species.<ref name=":9">{{Cite journal |last=Loo |first=Yen Yi |last2=Moran |first2=INES G. |last3=Cain |first3=Kristal E. |date=2019 |title=Grey warbler (Gerygone igata) aggressive behaviour towards rifleman (Acanthisitta chloris) fledglings |url=https://scholar.google.com/citations?view_op=view_citation&hl=en&user=NMHt1EsAAAAJ&citation_for_view=NMHt1EsAAAAJ:Tyk-4Ss8FVUC |journal=Notornis |volume=66 |issue=3 |pages=174–177}}</ref> For instance, it was discovered that the grey warbler has aggressive interspecific interactions with [[Rifleman (bird)|rifleman]] (''[[Rifleman (bird)|Acanthisitta chloris]]'').<ref name=":9" /> Grey warblers were observed during their breeding season to be chasing rifleman [[Fledgling (bird)|fledglings]].<ref name=":9" /> In each situation, the adult grey warbler would chase the young rifleman silently, while the riflemen would be producing frantic distress calls to their parents.<ref name=":9" /> These chases would vary in length of time and would usually result in the parent rifleman producing an alarm call that would ward off the warbler.<ref name=":9" /> However, adult warblers would never chase the adult rifleman, only the juveniles.<ref name=":9" /> Aggressive behaviour like this may result in niche displacement of the young rifleman, which would benefit the warbler as it would give them more access to important resource. Therefore, it can be understood that there are several reasons for why an adult warbler would perform this behaviour, for instance, to defend resources within its territory, or competition for food.<ref name=":9" /> The former seems more likely, as warblers have often been observed to solve territorial disputes by chasing individuals out of their territory, therefore successfully defending nests, food sources, fledglings, and mates.<ref name=":9" /> However, it needs to be noted that more time spent performing territory behaviours is costly, as it means less time spent doing other vital behaviours, for instance feeding young.<ref name=":8" /> This highlights how behaviours always have costs and benefits, and for a behaviour to be successful, the benefits must outweigh the costs. |
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==In Māori culture== |
==In Māori culture== |
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The direction in which a grey warbler would build its nest served as an indicator of forthcoming weather conditions to [[Māori people|Māori]] – in this respect, the bird was known as a ''manu tohu tau''.<ref name ="ForestLore">{{cite book |last=Best |first=E. |date=1977 |title=Forest lore of the Maori |url=http://nzetc.victoria.ac.nz/tm/scholarly/name-427176.html |location=Wellington, New Zealand |publisher=E.C. Keating}}</ref> The tradition states that a grey warbler will build the nest entrance in the opposite direction to the prevailing wind.<ref name="Keane">{{cite web |url=https://teara.govt.nz/en/nga-manu-birds/page-4 |title=Ngā manu – birds - Predicting the weather |last=Keane-Tuala |first=K. |date=2015 |website=Te Ara |access-date=2020-06-13}}</ref> As such, |
The direction in which a grey warbler would build its nest served as an indicator of forthcoming weather conditions to [[Māori people|Māori]] – in this respect, the bird was known as a ''manu tohu tau''.<ref name ="ForestLore">{{cite book |last=Best |first=E. |date=1977 |title=Forest lore of the Maori |url=http://nzetc.victoria.ac.nz/tm/scholarly/name-427176.html |location=Wellington, New Zealand |publisher=E.C. Keating}}</ref> The tradition states that a grey warbler will build the nest entrance in the opposite direction to the prevailing wind.<ref name="Keane">{{cite web |url=https://teara.govt.nz/en/nga-manu-birds/page-4 |title=Ngā manu – birds - Predicting the weather |last=Keane-Tuala |first=K. |date=2015 |website=Te Ara |access-date=2020-06-13}}</ref> As such, an eastern-facing entrance would indicate a poorly season brought on by western winds; in contrast, a northern-facing entrance would suggest a pleasant season ahead.<ref name ="ForestLore" /> |
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In spring, the song of the grey warbler is said to be a signal for Māori to begin planting their crops.<ref name ="Tauira">{{cite book |last=Metge |first=J. |date=2015 |title=Tauira: Māori methods of learning and teaching |location=Auckland, New Zealand |publisher=Auckland University Press}}</ref> As such, those who 'ignore' the call of the grey warbler and do not help out with the planting of crops (and later seek to reap the harvest for themselves) are rebuked with the following ''whakataukī'' (proverb): |
In spring, the song of the grey warbler is said to be a signal for Māori to begin planting their crops.<ref name ="Tauira">{{cite book |last=Metge |first=J. |date=2015 |title=Tauira: Māori methods of learning and teaching |location=Auckland, New Zealand |publisher=Auckland University Press}}</ref> As such, those who 'ignore' the call of the grey warbler and do not help out with the planting of crops (and later seek to reap the harvest for themselves) are rebuked with the following ''whakataukī'' (proverb): |
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==References== |
==References== |
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{{Reflist}} |
{{Reflist}} |
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== External links== |
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* [https://nzetc.victoria.ac.nz/tm/scholarly/tei-BulBird-t1-g1-t1-body-d0-d13.html Gerygone Flaviventris. — (Grey Warbler.) | NZETC] |
* [https://nzetc.victoria.ac.nz/tm/scholarly/tei-BulBird-t1-g1-t1-body-d0-d13.html Gerygone Flaviventris. — (Grey Warbler.) | NZETC] |
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Latest revision as of 05:04, 19 October 2024
Grey warbler | |
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Order: | Passeriformes |
Family: | Acanthizidae |
Genus: | Gerygone |
Species: | G. igata
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Binomial name | |
Gerygone igata | |
Synonyms | |
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The grey warbler (Gerygone igata), also known by its Māori name riroriro[3] or outside New Zealand as the grey gerygone, is an insectivorous bird in the family Acanthizidae endemic to New Zealand. It is sometimes known as the teetotum or rainbird.[4] Its natural habitat is forests, but also tends to occupy lower vegetation habitats.[5] These insectivorous birds feed on insects living in shrubs, and often feed on the wing.[5] They are found throughout New Zealand, as well as offshore islands where shrub exists.[6] In fact, these birds even flourish in suburban areas, as long as there is vegetation present.[6]
Description
[edit]The grey warbler has a long tail that is darker than its grey-brown body, with white tail end markings as well as a white tail underside.[6] There is little sexual dimorphism between males and females, aside from females usually being smaller than males.[5] Warblers are especially small; weighing around 6.5g with an average length of only around 10cm.[5] Adults have a signature ruby red eye, while juveniles have a brown eye, as well as yellowish feathers around the face and underbody.[5] Its nest is especially unique among birds, with a pear shaped, dome like hanging nest that has a circular side entrance hole.[5]
Song
[edit]The male's song often starts with a series of three squeaks and builds into a distinctive long plaintive wavering trill that rises and falls. Only the male warblers sing year-round, to attract mates and defend territory.[7] Male songs are particularly loud during summer and spring, which lines up with the warblers breeding season.[6] The warbler’s song is a pleasant, soft warble and varies between different populations.[6] In fact, studies looking at temporal aspects of warbler song found that the song shifted to a higher frequency over a period of 7 years.[8] It was hypothesised that this was due to the reintroduction of native species to the warbler’s habitat.[8] The purpose of the song is not only to attract a mate, but also to ward off potential threats that enter a warbler’s territory, whether that be predators or other warblers.[5]
Distribution and habitat
[edit]Grey warblers are common throughout New Zealand's main islands and many off-shore islands, but are absent from open country and alpine areas. At home in native and exotic forests it may be found almost anywhere there is some tree or shrub cover.[9]
Behaviour
[edit]Feeding
[edit]The grey warbler is a predominantly insectivorous bird, feeding on organisms such as spiders, beetles, and flies.[5] They do this by hovering around shrubs, and picking invertebrates off leaves.[5] However, they have been seen to occasionally eat fruits, perhaps to make up for limiting nutrients that are low in invertebrates, or due to their very high energy method of feeding.[5]
Breeding
[edit]The breeding season in grey warblers is especially long, lasting from August to January.[5] A breeding pair usually establishes a territory around late July to August, and defends this territory until the end of the breeding season.[7] Territories are defended by males by chasing away individuals, while also utilising loud, continuous singing.[5] Females also tend to join in with these chases and tend to have a higher chance of joining the chase if an individual gets too close to the nest.[5] In terms of mating behaviours, males sing all year around, and this identifies the sex of the warbler as there is no clear sexual dimorphism in the species aside from size.[7] Males also perform a wing fluttering behaviour, involving rapid flapping of their wings.[7] This is perhaps an effort to increase the strength of the pair bond and synchronise with their partners behaviour, as the display occurs throughout all stages of breeding, especially when the female is present.[7]
Nesting and Parental Care
[edit]Grey warblers are unique among New Zealand birds in building a pear-shaped nest with a side entrance near the top. Breeding season in the grey warbler lasts 6 months, from the first building to the last fledging.[7] Their season starts early, and as a result they often complete building and laying before the last day.[7] The early start for the season is likely due to parasitism by the shining cuckoo, Chrysococcyx lucidus.[6] The early start allows the warbler chicks to be out of the nest by the time the cuckoos’ season starts (around September or October), and therefore only the second clutch is impacted.[6] Grey warblers’ nest in a range of different small-leaved trees and shrubs, especially kānuka.[10] Only females gather materials and build the nest, spending from 7-27 days to complete the pear-shaped nest.[7][10] Males do, however, accompany the females on trips away from the nest, likely as an act of mate defence.[7] These nests consist of a range of materials; the outside of the nest is often composed of stout material (for instance rootlets), as well as moss and sheep’s wool, all bound together using cobwebs.[10] Some of the nests also have a middle layer of wool or clematis seeds.[10] The variation in nest materials often aligns with what is available in the warbler’s home range.[10]
After building, female warblers often only delay around 8 days before laying their eggs.[7] Due to this fast turnover, nests found later in the breeding season are often difficult to find.[7] Laying of eggs occurs over 15-16 weeks of the year, and the first clutch is laid at different times during a 6-week period.[7] One clutch is often around 2-5 eggs, and there is at least a 2-day gap between the laying of each egg.[5] Incubation occurs when the last egg is laid, where only the female incubates for a period of 17-21 days.[7] Once hatched, the young warblers don’t leave the nest for around 17 days, and once they have left the nest are still fed for around 35 days.[5] Over the whole laying period, the grey warbler only produces two clutches at a slow rate over the long breeding season.[7] This is likely due to New Zealand’s mild conditions, which results in food not declining over the winter.[7] Therefore, the warbler’s population size will always be close to the limit set by resource availability, so there is reduced ability for extra breeding due to energy limitations.
Both sexes spend time feeding young.[10] Grey Warblers will feed their young solely with small invertebrates, but traces of grass were seen in the gut of young warblers, likely due to accidental ingestion.[10] Once food has been delivered to the nest, parents often remove the gelatinous faecal sacs produced by the nestlings, before moving to a perch 15m away from the nest to dispose of the sacs.[10]
Begging
[edit]In avian species, begging behaviour is very common in young hatchlings, to capture the attention of a parent bird to gain access to more food.[11] Often, the level of begging will differ depending on different factors, for instance hunger level and age.[11] As with most animal behaviour, there is always a toss-up between the costs and the benefits of the behaviour; in this case, predation pressure will increase with more begging from young.[12] In other bird species, studies have highlighted the positive correlation between increased begging behaviour and predation risk, especially for birds nesting at ground level.[13] The begging behaviour of the grey warbler is especially unique, with many factors influencing how a parent responds to begging calls in its offspring. For instance, the adult grey warbler uses specific behaviours to reduce the predation pressure of the hatchlings' begging. Parents can utilise a switch-off signal/call, to communicate with its young when predators are present, and therefore stop the begging of the hatchlings to avoid being located by the predators.[14] This is a feature of a lot of avian species, but studies discovered that after alarm calls, rather than ceasing begging, grey warbler hatchlings would change the structure of their call.[14] This behaviour functions to reduce the cost of the begging behaviour, by increasing chance of being fed while also decreasing predation pressures.[14]
Grey warbler hatchlings also alter their call depending on hunger and age.[11] Studies highlighted that as a chick became hungrier, call structure narrowed in frequency range, while decreasing in amplitude.[11] Furthermore, as a chick aged, duration decreased, and frequency increased.[11] These differences in call structure with age and hunger highlight that begging in grey warbler hatchlings is far more complex than just begging for food; the type of call will communicate to the parent what state it is in, and therefore determine the amount of food a chick may receive.[11] There are also interspecific impacts of these specific begging calls. For instance, the brood parasite Chrysococcyx lucidus (shining cuckoo) parasitises the grey warbler by laying its eggs into grey warbler nests during the second clutch, resulting in the parent grey warblers having to raise the cuckoo’s young.[13] This can have major consequences, as cuckoo chicks grow larger than warbler chicks, so often end up pushing the young warblers out of the nest.[5] For the cuckoo hatchling to survive and be successful, it needs to identically mimic the grey warbler chicks begging behaviour. The complexity of grey warbler begging may mean that the cuckoo will also have to match these highly specific calls.[11]
Aggression and territoriality
[edit]As mentioned, warblers set up territories just prior to breeding season, and therefore show aggressive behaviours to defend those territories.[5] Studies indicated that the grey warbler displays very strong territorial behaviours in comparison to other birds.[15] Males spend a smaller proportion of their time feeding chicks than other birds living in the same niche, and therefore have more time to perform vigilance and territorial behaviours.[15] Warbler males also spend a significant amount of time mate guarding; for instance, when the female is gathering materials to build the nest.[15] Studies highlighted the aggressive interspecific behaviour grey warblers show towards other bird species.[16] For instance, it was discovered that the grey warbler has aggressive interspecific interactions with rifleman (Acanthisitta chloris).[16] Grey warblers were observed during their breeding season to be chasing rifleman fledglings.[16] In each situation, the adult grey warbler would chase the young rifleman silently, while the riflemen would be producing frantic distress calls to their parents.[16] These chases would vary in length of time and would usually result in the parent rifleman producing an alarm call that would ward off the warbler.[16] However, adult warblers would never chase the adult rifleman, only the juveniles.[16] Aggressive behaviour like this may result in niche displacement of the young rifleman, which would benefit the warbler as it would give them more access to important resource. Therefore, it can be understood that there are several reasons for why an adult warbler would perform this behaviour, for instance, to defend resources within its territory, or competition for food.[16] The former seems more likely, as warblers have often been observed to solve territorial disputes by chasing individuals out of their territory, therefore successfully defending nests, food sources, fledglings, and mates.[16] However, it needs to be noted that more time spent performing territory behaviours is costly, as it means less time spent doing other vital behaviours, for instance feeding young.[15] This highlights how behaviours always have costs and benefits, and for a behaviour to be successful, the benefits must outweigh the costs.
In Māori culture
[edit]The direction in which a grey warbler would build its nest served as an indicator of forthcoming weather conditions to Māori – in this respect, the bird was known as a manu tohu tau.[17] The tradition states that a grey warbler will build the nest entrance in the opposite direction to the prevailing wind.[18] As such, an eastern-facing entrance would indicate a poorly season brought on by western winds; in contrast, a northern-facing entrance would suggest a pleasant season ahead.[17]
In spring, the song of the grey warbler is said to be a signal for Māori to begin planting their crops.[19] As such, those who 'ignore' the call of the grey warbler and do not help out with the planting of crops (and later seek to reap the harvest for themselves) are rebuked with the following whakataukī (proverb):
I whea koe i te tangihanga o te riroriro, ka mahi kai māu?
Where were you when the riroriro was singing, that you didn’t work to get yourself food?[18]
Gallery
[edit]References
[edit]- ^ BirdLife International (2016). "Gerygone igata". IUCN Red List of Threatened Species. 2016: e.T22704735A93982871. doi:10.2305/IUCN.UK.2016-3.RLTS.T22704735A93982871.en. Retrieved 11 November 2021.
- ^ Quoy and Gaimard, in Dumont d’Urville, 1832. Curruca igata (protonym). Voyage de la corvette l'Astrolabe, Zool., 1, p. 201, Atlas, 1833, Oiseaux, pl. 11, fig. 2 BHL
- ^ TPH 7/7/1905 p3 http://www.maoridictionary.co.nz/search?idiom=&phrase=&proverb=&loan=&keywords=Riroriro&search=
- ^ "Grey warbler | Riroriro". New Zealand Birds Online. Retrieved 12 October 2024.
- ^ a b c d e f g h i j k l m n o p q Heather, B.D; Robertson, H.A. (2005). The Field Guide to the Birds of New Zealand. Auckland: Penguin Books. pp. 146, 148, 149, 391, 392.
{{cite book}}
: CS1 maint: date and year (link) - ^ a b c d e f g Chambers, S (2009). Birds of New Zealand - Locality Guide (3rd ed.). Orewa, New Zealand: Arun Books. pp. 241–242.
{{cite book}}
: CS1 maint: date and year (link) - ^ a b c d e f g h i j k l m n o Gill, Brian J. (1982). "BREEDING OF THE GREY WARBLER GERYGONE IGATA AT KAIKOURA, NEW ZEALAND". Ibis. 124 (2): 123–147. doi:10.1111/j.1474-919X.1982.tb03752.x. ISSN 0019-1019.
- ^ a b Azar, Joseph F.; Bell, Ben D.; Borowiec, Marta (2014). "Temporal change of the song of a local population of the Grey Warbler ( Gerygone igata ): has its song changed over time?". Emu - Austral Ornithology. 114 (1): 80–85. doi:10.1071/MU13039. ISSN 0158-4197.
- ^ Atlas Of Bird Distribution In New Zealand 1999–2004 - Ornithological Society of New Zealand http://notornis.osnz.org.nz/bird-distribution-atlas-1999-2004-last-gasp-field Archived 2021-07-11 at the Wayback Machine
- ^ a b c d e f g h Gill, B.J. (1983). "Breeding habits of the Grey Warbler (Gerygone igata)". Notornis. 30 (2): 137–165.
- ^ a b c d e f g Anderson, Michael G.; Brunton, Dianne H.; Hauber, Mark E. (2010). "Reliable Information Content and Ontogenetic Shift in Begging Calls of Grey Warbler Nestlings". Ethology. 116 (4): 357–365. doi:10.1111/j.1439-0310.2010.01750.x. ISSN 0179-1613.
- ^ "Experimental evidence that nestling begging behaviour incurs a cost due to nest predation". Proceedings of the Royal Society of London. Series B: Biological Sciences. 257 (1349): 161–164. 1994-08-22. doi:10.1098/rspb.1994.0110. ISSN 0962-8452.
- ^ a b Gill, Brian J. (1983). "Brood‐parasitism by the Shining Cuckoo Chrysococcyx lucidus at Kaikoura, New Zealand". Ibis. 125 (1): 40–55. doi:10.1111/j.1474-919X.1983.tb03082.x. ISSN 0019-1019.
- ^ a b c Anderson, Michael G.; Brunton, Dianne H.; Hauber, Mark E. (2010-02-01). "Species specificity of grey warbler begging solicitation and alarm calls revealed by nestling responses to playbacks". Animal Behaviour. 79 (2): 401–409. doi:10.1016/j.anbehav.2009.11.017. ISSN 0003-3472.
- ^ a b c d Cameron, Heather B. (1990). Spacing behaviour, time budgets and territoriality in rifleman (Acanthisitta chloris chloris) and grey warbler (Gerygone igata) at Kowhai Bush (MSc thesis). University of Canterbury. doi:10.26021/8904. Retrieved 12 October 2024.
- ^ a b c d e f g h Loo, Yen Yi; Moran, INES G.; Cain, Kristal E. (2019). "Grey warbler (Gerygone igata) aggressive behaviour towards rifleman (Acanthisitta chloris) fledglings". Notornis. 66 (3): 174–177.
- ^ a b Best, E. (1977). Forest lore of the Maori. Wellington, New Zealand: E.C. Keating.
- ^ a b Keane-Tuala, K. (2015). "Ngā manu – birds - Predicting the weather". Te Ara. Retrieved 2020-06-13.
- ^ Metge, J. (2015). Tauira: Māori methods of learning and teaching. Auckland, New Zealand: Auckland University Press.
External links
[edit]- NZ Royal Forest and Bird Protection Society, Nov 2003
- Gerygone Flaviventris. — (Grey Warbler.) | NZETC