Misplaced Pages

#402597

49-449: The plumbeous seedeater ( Sporophila plumbea ) is a species of bird in the family Thraupidae . It is found in Argentina , Bolivia , Brazil , Colombia , French Guiana , Guyana , Paraguay , Peru , Suriname , and Venezuela . Its natural habitats are dry savanna and subtropical or tropical seasonally wet or flooded lowland grassland . This article about a tanager

98-700: A better sense of smell. A third stage of bird evolution starting with Ornithothoraces (the "bird-chested" avialans) can be associated with the refining of aerodynamics and flight capabilities, and the loss or co-ossification of several skeletal features. Particularly significant are the development of an enlarged, keeled sternum and the alula , and the loss of grasping hands. † Anchiornis † Archaeopteryx † Xiaotingia † Rahonavis † Jeholornis † Jixiangornis † Balaur † Zhongjianornis † Sapeornis † Confuciusornithiformes † Protopteryx † Pengornis Ornithothoraces † Enantiornithes Polygyny in animals Polygyny

147-473: A definition similar to "all theropods closer to birds than to Deinonychus ", with Troodon being sometimes added as a second external specifier in case it is closer to birds than to Deinonychus . Avialae is also occasionally defined as an apomorphy-based clade (that is, one based on physical characteristics). Jacques Gauthier , who named Avialae in 1986, re-defined it in 2001 as all dinosaurs that possessed feathered wings used in flapping flight , and

196-510: A few females are able to mate with another male, while not being watched by the breeding male. (Some studies also show that EPC is less common in polygyny compared to monogamy. ) These breeding males also have short tenure, and it is common for groups of males who do not have harems to attack a breeding male in order to gain reproductive access to his females. In some cases, polygyny can lead to aggression between males. An example of species that exhibit male-male aggression under polygynous system

245-442: A group called Paraves . Some basal members of Deinonychosauria, such as Microraptor , have features which may have enabled them to glide or fly. The most basal deinonychosaurs were very small. This evidence raises the possibility that the ancestor of all paravians may have been arboreal , have been able to glide, or both. Unlike Archaeopteryx and the non-avialan feathered dinosaurs, who primarily ate meat, studies suggest that

294-409: A plausible reason as to why females prefer older males. Although highly debated, female choice in the great reed warbler may be explained by the good genes theory . False paternity and decreased offspring survival are two factors which might contribute to a decrease in male fitness. From an evolutionary standpoint, the most predominant characteristic that is often found in polygynous mating systems

343-422: A polygynous mating system is the increased fitness and reproductive success of the lone male because he will father all the offspring. Being the sole male of a harem is highly advantageous for the male because he has a much higher chance of his progeny surviving, which means he is passing on his genes to more individuals. Due to the fact that one male sires all of the offspring there is less genetic diversity in

392-403: A preference to mate with males with larger song repertoires, because this indicates that they are older and may have better nesting territories. Also, female grayling butterflies ( Hipparchia semele ) choose males based on their performance in flight competitions, where the winning male settles in the territory best for oviposition. Female Coquerel's sifaka ( Propithecus coquereli ) mate with

441-455: A resource, males pursue a resource defense strategy and polygyny occurs when the females are clumped and the offspring require little to no parental care (e.g. yellow-bellied marmots , orange-rumped honeyguides ). In polygynous systems there is less genetic diversity due to the fact that one male sires all of the offspring. Additionally, it is difficult for males to monopolize many females at once, leading to extra-pair copulations in which

490-482: A second female to impregnate, once the first female has laid her eggs. Strongly polygynous or monogamous species display increased female–female aggression. Many factors affect female aggression including predator density, habitat quality, nest spacing, and territory size. Often, females will fight for resources from the male, such as food and nest protection. The female disadvantages of mating with an already-mated male bird can be overcome with ample resources provided by

539-406: A sister group, the order Crocodilia , contain the only living representatives of the reptile clade Archosauria . During the late 1990s, Aves was most commonly defined phylogenetically as all descendants of the most recent common ancestor of modern birds and Archaeopteryx lithographica . However, an earlier definition proposed by Jacques Gauthier gained wide currency in the 21st century, and

SECTION 10

#1732801819403

588-717: A time, sometimes for years, and rarely for life. Other species have breeding systems that are polygynous (one male with many females) or, rarely, polyandrous (one female with many males). Birds produce offspring by laying eggs which are fertilised through sexual reproduction . They are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching. Many species of birds are economically important as food for human consumption and raw material in manufacturing, with domesticated and undomesticated birds being important sources of eggs, meat, and feathers. Songbirds , parrots, and other species are popular as pets. Guano (bird excrement)

637-436: Is Allobates femoralis . Physical aggression can be induced by territorial defense and competition in courtship. Especially, during the courtship march, a competing male can intercept the female while the male who originally courted the female searches for an oviposition site. In this case, the physical aggression between males can last about 15 minutes until one of the males leave the site. The largest advantage for males in

686-413: Is a stub . You can help Misplaced Pages by expanding it . Bird Birds are a group of warm-blooded vertebrates constituting the class Aves ( Latin: [ˈaveːs] ), characterised by feathers , toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart , and a strong yet lightweight skeleton . Birds live worldwide and range in size from

735-423: Is correlated with an increase in harem size and increased male fitness because females prefer to mate with males that have a more extensive song repertoire. It is also possible that broad song repertoires are a supplementary cue for a good mate, in conjunction with male territory size and quality. A wide-ranging song repertoire develops with age, and older males are more likely to dominate better territories, giving

784-443: Is extreme sexual dimorphism . Sexual dimorphism, or the difference in size or appearance between males and females, gives males an advantage in fights against each other to demonstrate dominance and win over harems. Sexual dimorphism can present in larger body size and canine size. Polygyny is beneficial in particular to the male, because he has a greater increase in fitness and reproductive success. This increase consequently reduces

833-429: Is harvested for use as a fertiliser. Birds figure throughout human culture. About 120 to 130 species have become extinct due to human activity since the 17th century, and hundreds more before then. Human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them. Recreational birdwatching is an important part of the ecotourism industry. The first classification of birds

882-447: Is most commonly observed. Evolutionarily speaking, polygyny in birds might have evolved because many females do not require male support to care for their offspring. Because females do not need extra help raising their nests, males can afford to invest in multiple females. Nonetheless, male parental care is often found in many polygynous territorial bird species, leading to female competition for male assistance. Most often, males will seek

931-503: Is not considered a direct ancestor of birds, though it is possibly closely related to the true ancestor. Over 40% of key traits found in modern birds evolved during the 60 million year transition from the earliest bird-line archosaurs to the first maniraptoromorphs , i.e. the first dinosaurs closer to living birds than to Tyrannosaurus rex . The loss of osteoderms otherwise common in archosaurs and acquisition of primitive feathers might have occurred early during this phase. After

980-400: Is only half as common as in socially monogamous birds. Some ethologists consider this finding to be support for the 'female choice' hypothesis of mating systems in birds. A polygynous leader male will always be the best mating choice before he is beaten by another male, so it is harder for females to find a partner better than their mate in polygyny as compared to monogamy. This might reduce

1029-516: Is synonymous to Avifilopluma. † Scansoriopterygidae † Eosinopteryx † Jinfengopteryx † Aurornis † Dromaeosauridae † Troodontidae Avialae Based on fossil and biological evidence, most scientists accept that birds are a specialised subgroup of theropod dinosaurs and, more specifically, members of Maniraptora , a group of theropods which includes dromaeosaurids and oviraptorosaurs , among others. As scientists have discovered more theropods closely related to birds,

SECTION 20

#1732801819403

1078-434: Is typical of one-male, multi-female groups and can be found in many species including: elephant seal , spotted hyena , gorilla , red-winged prinia , house wren , hamadryas baboon , common pheasant , red deer , Bengal tiger , Xylocopa sonorina , Anthidium manicatum and elk . Often in polygynous systems, females will provide the majority of parental care. When two animals mate, they both share an interest in

1127-535: Is used by many scientists including adherents to the PhyloCode . Gauthier defined Aves to include only the crown group of the set of modern birds. This was done by excluding most groups known only from fossils , and assigning them, instead, to the broader group Avialae, on the principle that a clade based on extant species should be limited to those extant species and their closest extinct relatives. Gauthier and de Queiroz identified four different definitions for

1176-669: The Tiaojishan Formation of China, which has been dated to the late Jurassic period ( Oxfordian stage), about 160 million years ago. The avialan species from this time period include Anchiornis huxleyi , Xiaotingia zhengi , and Aurornis xui . The well-known probable early avialan, Archaeopteryx , dates from slightly later Jurassic rocks (about 155 million years old) from Germany . Many of these early avialans shared unusual anatomical features that may be ancestral to modern birds but were later lost during bird evolution. These features include enlarged claws on

1225-575: The only known living dinosaurs . Likewise, birds are considered reptiles in the modern cladistic sense of the term, and their closest living relatives are the crocodilians . Birds are descendants of the primitive avialans (whose members include Archaeopteryx ) which first appeared during the Late Jurassic . According to recent estimates, modern birds ( Neornithes ) evolved in the Late Cretaceous and diversified dramatically around

1274-433: The 5.5 cm (2.2 in) bee hummingbird to the 2.8 m (9 ft 2 in) common ostrich . There are over 11,000 living species and they are split into 44 orders . More than half are passerine or "perching" birds. Birds have wings whose development varies according to species; the only known groups without wings are the extinct moa and elephant birds . Wings, which are modified forelimbs , gave birds

1323-480: The ability to fly, although further evolution has led to the loss of flight in some birds , including ratites , penguins , and diverse endemic island species. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds , have further evolved for swimming. The study of birds is called ornithology . Birds are feathered theropod dinosaurs and constitute

1372-428: The appearance of Maniraptoromorpha, the next 40 million years marked a continuous reduction of body size and the accumulation of neotenic (juvenile-like) characteristics. Hypercarnivory became increasingly less common while braincases enlarged and forelimbs became longer. The integument evolved into complex, pennaceous feathers . The oldest known paravian (and probably the earliest avialan) fossils come from

1421-509: The birds that descended from them. Despite being currently one of the most widely used, the crown-group definition of Aves has been criticised by some researchers. Lee and Spencer (1997) argued that, contrary to what Gauthier defended, this definition would not increase the stability of the clade and the exact content of Aves will always be uncertain because any defined clade (either crown or not) will have few synapomorphies distinguishing it from its closest relatives. Their alternative definition

1470-403: The community, which is disadvantageous to females. Additionally, females sometimes encounter infanticide , which is when a breeding male is overthrown and a new breeding male becomes dominant and kills all of their current offspring, as he has not fathered them. Because the females no longer have offspring to nurse, they will go into estrous sooner, which allows the new breeding male to mate with

1519-665: The earliest members of Aves, is removed from this group, becoming a non-avian dinosaur instead. These proposals have been adopted by many researchers in the field of palaeontology and bird evolution , though the exact definitions applied have been inconsistent. Avialae, initially proposed to replace the traditional fossil content of Aves, is often used synonymously with the vernacular term "bird" by these researchers. † Coelurus † Ornitholestes † Ornithomimosauria † Alvarezsauridae † Oviraptorosauria   Paraves Most researchers define Avialae as branch-based clade, though definitions vary. Many authors have used

Plumbeous seedeater - Misplaced Pages Continue

1568-475: The female will enter into a polygynous mating system, since she would still benefit from acquiring more resources. The polygyny threshold model can be applied to more than two females, provided there are enough resources to support them. The great reed warbler ( Acrocephalus arundinaceus ) is one of the few bird species that is polygynous and has a harem. Males provide resources to their harem, such as nest protection and varying levels of parental care. Females in

1617-458: The females earlier. Some females willingly choose polygyny in order to gain access to the "best" resources available. In these cases, the benefits from superior resource access must outweigh the opportunity cost of giving up monogamous parental care by a male. They also can get support from the same group of other females when in danger, like a female lion. Females in polygyny may have less extra-pair copulation. In socially polygynous birds, EPP

1666-451: The first avialans were omnivores . The Late Jurassic Archaeopteryx is well known as one of the first transitional fossils to be found, and it provided support for the theory of evolution in the late 19th century. Archaeopteryx was the first fossil to display both clearly traditional reptilian characteristics—teeth, clawed fingers, and a long, lizard-like tail—as well as wings with flight feathers similar to those of modern birds. It

1715-498: The genetic diversity of the community, often leading to increased inbreeding. However, polygyny is not a particularly beneficial mating system for females, because their mate choice is limited to one male. Extra-pair copulations are a strategy used by females to avoid the sexual conflict caused by polygyny, allowing them access to better mate choice . Unlike in males, extra-pair copulations are advantageous for females because they present females with more mate choice as well as increase

1764-554: The genetic diversity of the community. Extra-pair copulations exemplify sexual conflict , a situation in which one behavior is advantageous for one sex, but disadvantageous for the other. Female choice, the act in which a female chooses her mate based on the attractiveness of his qualities, is very common in polygynous systems. In these cases, females will choose males based on secondary sexual characteristics, which may indicate access to better and more resources. For example, female great reed warblers ( Acrocephalus arundinaceus ) have

1813-409: The harem are able to breed at the same time, indicating that harem size and the number of male offspring are related. The most important factor when determining male fitness is the order in which he arrives to the territory. Males who arrive earlier increase the likelihood that they will obtain good nesting sites, improving their odds for attracting more females. Additionally, a greater song repertoire

1862-502: The limited sex will employ. Polygyny will occur when resources are localized and females form clusters, making it easier for males to control them. The various types of polygyny result because of the differential access individuals have to resources. When females continually move and are not spatially stable, males pursue a mate defense strategy. When the females are clumped, four types of polygyny occur. (Adapted from Dr. Susan Alberts ) When females are spatially stable in and around

1911-464: The male, resulting in female choice. In 1977, Stephen T. Emlen and Lewis W. Oring created a mating systems model that shows how resource distribution affects female living patterns and subsequently, mating systems. In a mating system, the limiting sex (usually females) is the one that the limited sex (usually males) tries to monopolize. The combination of resource distribution, parental care, and female breeding synchrony determines what mating strategies

1960-403: The number of females at risk for EPC once their mate finds out. An explanation for why polygynous systems persist is explained by the polygyny threshold model . This model demonstrates the link between female reproductive success and territory quality or the quality of a breeding situation. The polygyny threshold model also shows the effects of female reproductive success when multiple females in

2009-402: The outermost half) can be seen in the evolution of maniraptoromorphs, and this process culminated in the appearance of the pygostyle , an ossification of fused tail vertebrae. In the late Cretaceous, about 100 million years ago, the ancestors of all modern birds evolved a more open pelvis, allowing them to lay larger eggs compared to body size. Around 95 million years ago, they evolved

Plumbeous seedeater - Misplaced Pages Continue

2058-536: The previously clear distinction between non-birds and birds has become blurred. By the 2000s, discoveries in the Liaoning Province of northeast China, which demonstrated many small theropod feathered dinosaurs , contributed to this ambiguity. The consensus view in contemporary palaeontology is that the flying theropods, or avialans , are the closest relatives of the deinonychosaurs , which include dromaeosaurids and troodontids . Together, these form

2107-452: The same biological name "Aves", which is a problem. The authors proposed to reserve the term Aves only for the crown group consisting of the last common ancestor of all living birds and all of its descendants, which corresponds to meaning number 4 below. They assigned other names to the other groups.   Lizards & snakes   Turtles   Crocodiles   Birds Under the fourth definition Archaeopteryx , traditionally considered one of

2156-404: The same territory mate with one male. In this situation, the female has the option of breeding with an unmated male in a poor-quality territory or with an already-mated male in a high-quality territory. The second breeding female will receive fewer resources from the male than the first breeding female. However, if the bigamous threshold is higher than the second female's original resource threshold,

2205-551: The second toe which may have been held clear of the ground in life, and long feathers or "hind wings" covering the hind limbs and feet, which may have been used in aerial maneuvering. Avialans diversified into a wide variety of forms during the Cretaceous period. Many groups retained primitive characteristics , such as clawed wings and teeth, though the latter were lost independently in a number of avialan groups, including modern birds (Aves). Increasingly stiff tails (especially

2254-487: The success of the offspring, though often to different extremes. Unless the male and female are perfectly monogamous, meaning that they mate for life and take no other partners, even after the original mate's death, the amount of parental care will vary. Instead, it is much more common for polygynous mating to happen. Polygynous structures (excluding leks) are estimated to occur in up to 90% of mammals. Polygyny in birds occurs infrequently when compared to mammals, as monogamy

2303-600: The time of the Cretaceous–Paleogene extinction event 66 million years ago, which killed off the pterosaurs and all non- ornithuran dinosaurs. Many social species preserve knowledge across generations ( culture ). Birds are social, communicating with visual signals, calls, and songs , and participating in such behaviour as cooperative breeding and hunting, flocking , and mobbing of predators. The vast majority of bird species are socially (but not necessarily sexually) monogamous , usually for one breeding season at

2352-471: The winners of battles for the harem because the male has shown that he is stronger than another, potentially offering more protection from predators. Female red-winged blackbirds ( Agelaius phoeniceus ) exhibit aggression toward other females upon intrusion into the harem, usually heightened around breeding season. This behavior demonstrates that the females are protecting their breeding male from intruding females, suggesting they are preventing female access to

2401-466: Was developed by Francis Willughby and John Ray in their 1676 volume Ornithologiae . Carl Linnaeus modified that work in 1758 to devise the taxonomic classification system currently in use. Birds are categorised as the biological class Aves in Linnaean taxonomy . Phylogenetic taxonomy places Aves in the clade Theropoda as an infraclass or a subclass, more recently a subclass. Aves and

#402597