View source for Aegolius

{{Short description|Genus of birds}}
{{Italic title}}
{{Automatic taxobox
| name = ''Aegolius''
| image = Aegolius-funereus-001.jpg
| image_caption = Boreal owl (''Aegolius funereus'')
| taxon = Aegolius
| authority = [[Johann Jakob Kaup|Kaup]], 1829
| type_species = ''[[Boreal owl|Strix tengmalmi]]''<ref name=HM4>{{cite web |url= https://www.aviansystematics.org/4th-edition-checklist?viewfamilies=72 |title= Strigidae |author=<!--Not stated--> |date= |website= aviansystematics.org |publisher= The Trust for Avian Systematics |access-date= 2023-07-26}}</ref> = ''Strix funereus''
| type_species_authority = [[Carl Linnaeus|Linnaeus]], 1758
| subdivision_ranks = Species
| subdivision = See text
}}
'''''Aegolius''''' is a genus of small [[true owl]]s. The genus name is from [[Latin]], ''aegolius'', is a type of screech owl that was thought to be a bird of ill omen.
==Taxonomy==
The genus ''Aegolius'' was introduced in 1829 by the German naturalist [[Johann Jakob Kaup]] with the [[boreal owl]] (''Aegolius funereus'') as the [[type species]].<ref>{{ cite book | last=Kaup  | first=Johann Jakob  | author-link=Johann Jakob Kaup | year=1829 | title=Skizzirte Entwickelungs-Geschichte und natürliches System der europäischen Thierwelt | volume=c. 1 | language=German | place=Darmstadt  | publisher=Carl Wilhelm Leske | page=34 | url=https://www.biodiversitylibrary.org/page/41576419 }}</ref><ref>{{ cite book | editor-last=Peters | editor-first=James Lee | editor-link=James L. Peters | year=1940 | title=Check-List of Birds of the World | volume=4 | publisher=Harvard University Press | place=Cambridge, Massachusetts  | pages=171–172 | url=https://www.biodiversitylibrary.org/page/14476642 }}</ref> The genus name is [[Latin]] for a [[screech owl]], the word came from the [[Ancient Greek]] ''aigōlios'' meaning "a bird of ill omen".<ref>{{cite book | last=Jobling | first=James A. | year=2010| title=The Helm Dictionary of Scientific Bird Names | publisher=Christopher Helm | location=London | isbn=978-1-4081-2501-4 | page=33 | url=https://archive.org/stream/Helm_Dictionary_of_Scientific_Bird_Names_by_James_A._Jobling#page/n33/mode/1up  }}</ref> In [[Greek mythology]], [[Aegolius (mythology)|Aegolius]] was originally a man whom [[Zeus]] transformed into an owl.<ref>[[Antoninus Liberalis]], ''Metamorphoses'' [https://topostext.org/work/216#19 19]</ref>
==Species==
The genus contains five species:<ref name=ioc>{{cite web| editor1-last=Gill | editor1-first=Frank | editor1-link=Frank Gill (ornithologist) | editor2-last=Donsker | editor2-first=David | editor3-last=Rasmussen | editor3-first=Pamela | editor3-link=Pamela Rasmussen | date=January 2021 | title=Owls | work=IOC World Bird List Version 11.1 | url=https://www.worldbirdnames.org/bow/owls/ | publisher=International Ornithologists' Union | access-date=22 May 2021 }}</ref>
* [[Boreal owl]] or Tengmalm's owl, ''Aegolius funereus''
* [[Northern saw-whet owl]], ''Aegolius acadicus''
*† [[Bermuda saw-whet owl]], ''Aegolius gradyi'' ([[extinct]])
* [[Unspotted saw-whet owl]], ''Aegolius ridgwayi''
* [[Buff-fronted owl]], ''Aegolius harrisii''
== Description ==
''Aegolius'' owls are small, stout, short-tailed, and broad-winged, with large, round facial discs. The species varies from 18 to 27&nbsp;cm in length. These owls take mainly [[rodent]]s and other small [[mammal]]s as their prey, but also feed on [[bird]]s, [[bat]]s, [[insect]]s, and other invertebrates according to what is available. They are dark brown or black above, and whitish or buff below, marked with streaks or spots in the two northern forms. The head is large, with yellow eyes and a well-defined facial disc. The flight is strong, agile, and direct. They breed in tree holes, laying several eggs. They have repetitive whistling calls in the breeding season.
== Distribution ==
Three of the extant species are restricted to the [[New World]], but the boreal owl has a circumpolar range through [[North America]],  [[Eurasia]], the [[Alps]], and the [[Rocky Mountains|Rockies]]. Essentially nocturnal woodland owls of temperate or colder climates; the two northern species breed in North America's [[conifer]]ous forests, and the unspotted saw-whet owl and buff-fronted owl ([[Central America|Central]] and [[South America]], respectively) are species of mountain, cloud, or oak forests. They are mainly resident birds, but the northern species at least sometimes [[bird migration|move]] south or to lower altitudes in autumn. The movements are difficult to monitor due to the problems of detecting these nocturnal owls outside the breeding season, when they are not calling.
== Mating system ==
''Aegolius'' owls have a very diverse [[mating system]] containing multiple strategies. Although there are five species within this genus, one of which is extinct, the majority of the information known about the mating system is based on research from the [[boreal owl]] (''A. funereus)'' and the [[northern saw-whet owl]] (''A. acadicus'') in North America.<ref name=":0">Johnsgard, P. A. (1988). North American owls: biology and natural history.</ref> Both species have been shown to exhibit both [[Monogamy in animals|monogamous]] and [[Animal sexual behaviour#Polygamy|polygamous]] lifestyles with a focus on [[wiktionary:bigyny|bigyny]].<ref>Marks, J. S., Doremus, J. H., & Cannings, R. J. (1989). Polygyny in the Northern Saw-whet Owl. ''The Auk'', ''106''(4), 732-734.</ref> However, the boreal owl has been shown to exhibit biandry as well.<ref>Solheim, R. (1983). Bigyny and biandry in  Tengmalm's Owl ''Aegolius funereus''. ''Ornis Scandinavica'', 51-57.</ref>
=== Mate choice ===
[[File:Aegolius Funereus Teritorial call - song.ogg|thumb|Territorial call of the boreal owl (''A.funereus'')]]
==== Vocalizations ====
[[Mate choice]] in this genus is largely related to auditory vocalizations (a form of [[sensory exploitation]]). A quiet species through most of the year, the northern saw-whet owl male produces a bell-like or “series song” advertisement call.<ref>Simpson, M. B. (1972) The saw-whet owl population of North Carolina's southern Great Balsam Mountains. ''Chat 36:39-47.''</ref><ref>Swengel, S. R., & Swengelº, A. B. (1981). Study of a Northern Saw-Whet Owl Population in Sauk County, Wisconsin'. ''METHODS'', ''178''(1953).</ref> Generally, it can be heard early morning or on bright nights from March – May (the breeding season) to attract females.<ref>Walker, L. W. (1974). ''The Book of Owls.'' New York: Alfred A. Knopf.</ref> The calls are believed to be relatively different between individuals, suggesting they may play a role in individual identification by the females.<ref>Otter, K. (1996). Individual Variation in the Advertising Call of Male Northern Saw-Whet Owls (Variación Individual en las Llamadas de Aegolius Acadicus). ''Journal of Field Ornithology'', 398-405.</ref> After pairing with a mate, vocalizations are very limited and appear to be related to territory or offspring defence.<ref>Johns, S., G. R. A. Ebel, and A. Johns. (1978). Observations on the nesting behaviour of the saw-whet owl in Alberta. ''Bluejay 36:36-38.''</ref>
In contrast, the boreal owl produces a “staccato song” starting around dusk, and ending around midnight in the late winter and early spring. The call serves to attract females and becomes increasingly persistent as time without a mate passes.<ref>Bondrup-Nielsen, S. (1978). Vocalizations, nesting and habitat preferences of the boreal owl ''(Aegolius funereus)'' in North America. M.S. thesis, Univ. of Toronto.</ref><ref>Bondrup-Nielsen, S. 1984. Vocalizations of the boreal owl, ''Aegolius funereus richardsoni,'' in North America. ''Canadian Field-Naturalist.'' 98: 191-97.</ref> Some research suggests that unlike the Northern saw-whet owl, a variation of the male call persists after mating throughout the reproductive cycle for defense, aggression, or to convey information about prey. This suggests that vocalization may be used in this species beyond mate attraction and possibly as a contact call.<ref>Meehan, R H. (1980). Behavioral significance of boreal owl vocalizations during the breeding season. M.S. thesis, University of Alaska, Fairbanks.</ref>
[[File:Aegolius funereus-nest.jpg|thumb|Typical boreal owl (''A. funereus'') nest]]
==== Nest and territory quality ====
Aside from vocalization, females in this genus may choose males based on nest or territory quality. For example, in  boreal owls, the number and quality of [[Nest box|nest holes or boxes]] defended by males is a factor in female reproductive effort.<ref name=":1">Carlsson, B. G. (1991). Recruitment of mates and deceptive behavior by male Tengmalm's owls. ''Behavioral Ecology and Sociobiology'', ''28''(5), 321-328.</ref> The number and quality of nests appear to serve a [[Mate choice|direct benefit]] to females (direct benefit hypothesis), as it provides protection from [[predation]], as well as access to food resources, as good nest quality can be indicated by access to prey (i.e. small mammals).<ref name=":1" /> Female boreal owls' reproductive success can decline in [[Polyterritoriality|polyterritorial]] polygamous situations, as females are unable to discriminate previously paired and unpaired males (also known as the deception hypothesis). It is also important to note that increasing polygamy levels leads to decreased reproductive success in secondary females.<ref name=":1" />  Limited research has been conducted into mate choice of the Northern saw-whet owl  in relation to territory quality. Some researchers suggest they follow a similar trend to boreal owls, where the quality of nests is a direct benefit to the female and therefore a determining factor.<ref name=":2">Marks, J. S., Nightingale, A., & McCullough, J. M. (2015). On the breeding biology of Northern Saw-whet Owls (''Aegolius acadicus''). ''Journal of Raptor Research'', ''49''(4), 486-497.</ref> Northern saw-whet owls' nest locations appear less linked to the availability of small mammals, as they have a greater variety of prey options and tend to be more nomadic after each breeding season.<ref name=":2" /><ref>Marks, J. S., & Doremus, J. H. (2000). Are northern saw-whet owls nomadic?. ''Journal of Raptor Research'', ''34''(4), 299-304</ref>
==== Reversed size dimorphism ====
Lastly, size of males may play a role in mate choice in some species. The males in this genus provide direct benefit to females such as protection, territory, and resources. As a result, large male size (and smaller female size) would theoretically be more advantageous. However, in the boreal owl, this is not the case. Females tend to be larger and heavier than the male mates they choose, some suggesting this is the result of the starvation hypothesis (selection acts on females to increase ability to withstand long periods of time without food in polygamous lifestyles).<ref name=":3">Korpimäki, E. (1986). Reversed size dimorphism in birds of prey, especially in Tengmalm's Owl Aegolius funereus: a test of the" starvation hypothesis". ''Ornis Scandinavica'', 326-332.</ref> Another theory suggests that females purposely choose short-winged, light males, as they would be able to hunt at lower energetic costs and compete for territory more efficiently than larger, long-winged individuals.<ref name=":3" /><ref name=":5">Hakkarainen, H., & Korpimäki, E. (1991). Reversed sexual size dimorphism in Tengmalm's Owl: Is small male size adaptive?. ''Oikos'', 337-346.</ref> This would provide the female with greater material benefits for her offspring.  Reversed [[size dimorphism]] is also observed in northern saw-whet owls, but the differences are much more difficult to observe, as the species is smaller overall; the role of this in mate choice is unclear.<ref>Earhart, C. M., & Johnson, N. K. (1970). Size dimorphism and food habits of North American owls. ''The Condor'', ''72''(3), 251-264.</ref>
=== Contests ===
Relating to the observed size dimorphism in males, most species compete for territory in this genus, as it indirectly relates to better female mates.<ref name=":3" /><ref name=":5" /><ref name=":1" /> The [[intraspecific competition]] tends to be dependent on individual flight ability, individuals that can fly more efficiently and effectively tend to get better territory.<ref name=":3" /> However, interspecific competition also plays a role. Species in this genus are often smaller than other owls that have similar ranges; as a result, they often are outcompeted for territory by other species.<ref name=":0" /><ref name=":6">Hakkarainen, H., & Korpimaki, E. (1996). Competitive and predatory interactions among raptors: an observational and experimental study. ''Ecology'', ''77''(4), 1134-1142.</ref> This is especially true in boreal owls, as their range overlaps with the much larger Ural (''[[Ural owl|Strix uralensis]])'' and Eurasian eagle owls (''[[Eurasian eagle-owl|Bubo bubo]])''. As a result, when these species are present, the boreal owl often mates with less desirable subdominant females.<ref name=":6" />[[File:Aegolius acadicus -Fossil, Oregon, USA -juvenile-8.jpg|thumb|Northern saw-whet owl (''A.acadicus'') juveniles.]]
=== Parental Care ===
[[File:Aegolius funereus juv.JPG|thumb|Boreal owl juveniles]]
[[Parental care]] in the boreal and northern saw-whet owls is quite similar; females [[Egg incubation|incubate]] and [[Offspring|brood]] eggs, while males often provide protection, and resources such as food and nesting sites.<ref name=":0" /> This trend likely applies across the species in this genus, as some species may be conspecifics (i.e. northern saw-whet and unspotted saw-whet owls).<ref>"Aegolius ridgwayi". [[Integrated Taxonomic Information System]]. Retrieved 15 April 2018</ref>
In boreal owls, the level of investment provided by the male is directly related to the level of parental care effort in brooding by the female.<ref name=":4">Zárybnická, M., & Vojar, J. (2013). Effect of male provisioning on the parental behavior of female Boreal Owls Aegolius funereus. ''Zoological Studies'', ''52''(1), 36.</ref> Increased resources (i.e. food) provided by the male during the nesting stage increases female effort in brooding of the offspring.<ref name=":4" /> This is similar to the differential allocation hypothesis, which suggests that females increase their reproductive effort overall when offspring are the result of ideal mates. Brooding behavior is key to the success of owl fledglings, so when males provide adequate food, females provide adequate care.<ref>Sheldon, B. C. (2000). Differential allocation: tests, mechanisms and implications. ''Trends in Ecology & Evolution'', ''15''(10), 397-402.</ref><ref name=":4" /> Fewer or lighter individual fledglings are produced as polygamy rate increases and the amount of male effort becomes increasingly important in predicting female brooding effort.<ref>Korpimäki, E. (1991). Poor reproductive success of polygynously mated female Tengmalm's owls: are better options available?. ''Animal Behaviour'', ''41''(1), 37-47.</ref>
Information on parental care effort is limited on the northern saw-whet owl, and likely related to male provisioning rates, the extent, however, is unclear. Current research examines the effect of habitat loss on the male provisioning rates.<ref>Hinam, H. L., & Clair, C. C. S. (2008). High levels of habitat loss and fragmentation limit reproductive success by reducing home range size and provisioning rates of Northern saw-whet owls. ''Biological Conservation'', ''141''(2), 524-535.</ref>
==References==
{{Reflist}}
{{Strigiformes|S.|state=collapsed}}
{{Taxonbar|from=Q310862}}
{{Authority control}}
[[Category:Aegolius| ]]
[[Category:Bird genera]]
[[Category:Taxa named by Johann Jakob Kaup]]