Editing Tree swallow (section)

==Survival==
The tree swallow has an average lifespan of 2.7 years<ref name="VleckVleck2011">{{cite journal|last1=Vleck|first1=Carol M.|last2=Vleck|first2=David|last3=Palacios|first3=Maria G.|title=Evolutionary ecology of senescence: a case study using tree swallows, ''Tachycineta bicolor''|journal=Journal of Ornithology|volume=152|issue=S1|year=2011|pages=203–211|issn=0021-8375|doi=10.1007/s10336-010-0629-2|bibcode=2011JOrni.152..203V |s2cid=25321642}}</ref> and a maximum of 12 years. About 79% of individuals do not survive their first year, and those that do face an annual mortality rate of 40% to 60%.<ref name="hbw"/> Most deaths are likely the result of cold weather, which reduces insect availability, leading to starvation.<ref name="Turner"/> Lifespan is associated with telomere length: a 2005 study that used return rates (to the breeding site of the previous year) as a proxy for survival found that those with the longest telomeres at one year of age had a predicted lifespan of 3.5 years, compared to the 1.2 years for those with the shortest telomeres.<ref name="HaussmanWinkler2005">{{Cite journal| doi = 10.1098/rsbl.2005.0301| issn = 1744-9561| volume = 1| issue = 2| pages = 212–214| last1 = Haussmann| first1 = Mark F.| last2 = Winkler| first2 = David W.| last3 = Vleck| first3 = Carol M.| title = Longer telomeres associated with higher survival in birds| journal = Biology Letters| date = 2005-06-22| pmid = 17148169| pmc = 1626238}}</ref> Whether short telomeres cause a reduction in fitness or are simply an indicator of it is unknown. Regardless, a 2016 thesis found that measures of condition were positively correlated with telomere length. Males also generally had longer telomeres than females, as did smaller-winged birds. Individuals with shorter telomeres may compensate for potential losses in fitness by increasing reproductive effort, whereas those with longer telomeres may decrease their investment, as evidenced by the smaller proportion of chicks females with longer telomeres fledged.<ref name="Belmaker2016">{{cite thesis|last=Belmaker|first=Amos|year=2016|title=The Role of Telomere Length in Tree Swallow Behavior and Life History|chapter=Patterns of co-variation of telomere length, condition, life history and fitness in a short-lived bird species|publisher=Cornell University|type=PhD}}</ref> Telomere length is highly heritable, and is especially dependent on that of the mother.<ref name="BelmakerHallinger2019">{{Cite journal| doi = 10.1002/ece3.5386| issn = 2045-7758| volume = 9| issue = 14| pages = 8175–8186| last1 = Belmaker| first1 = Amos| last2 = Hallinger| first2 = Kelly K.| last3 = Glynn| first3 = Rebbeca A.| last4 = Winkler| first4 = David W.| last5 = Haussmann| first5 = Mark F.| title = The environmental and genetic determinants of chick telomere length in tree swallows (''Tachycineta bicolor'')| journal = Ecology and Evolution| date = 2019| pmid = 31380080| pmc = 6662556| doi-access = free| bibcode = 2019EcoEv...9.8175B}}</ref>

===Predation===
The tree swallow is susceptible to a wide range of predators. Eggs, nestlings, and adults in the nest fall victim to [[Pantherophis obsoletus|black rat snakes]], [[American crow]]s, [[American kestrel]]s, [[common grackle]]s, [[northern flicker]]s, [[chipmunk]]s, [[Peromyscus|deermice]], [[domestic cat]]s, [[weasel]]s,<ref name= Winkler>Winkler, D. W.; Hallinger, K. K.; Ardia, D. R.; Robertson, R. J.; Stutchbury, B. J.; Chohen, R. R. (2011). Poole, A. F., ed. "Tree Swallow (''Tachycineta bicolor'')". ''The Birds of North America''. [[Ithaca, New York]]: Cornell Lab of Ornithology.</ref> [[American black bear]]s,<ref name="ZachMayoh1984">{{cite journal|last1=Zach|first1=Reto|last2=Mayoh|first2=Keith R.|title=Gamma radiation effects on nestling tree swallows|journal=Ecology|volume=65|issue=5|year=1984|pages=1641–1647|issn=0012-9658|doi=10.2307/1939142|jstor=1939142|bibcode=1984Ecol...65.1641Z }}</ref> and [[raccoon]]s.<ref>Chapman, L. B. (1955). "Studies of a tree swallow colony". ''Bird-Banding''. '''6''' (2): 45–70.</ref> While flying or perched, predators to the tree swallow include American kestrels, [[black-billed magpie]]s,<ref name= Winkler/> [[barred owl]]s,<ref>Errington, P. L. (1932). "Food habits of southern Wisconsin raptors. Part I. Owls". ''The Condor''. '''34''' (4): 176–186.</ref> [[great horned owl]]s, [[Merlin (bird)|merlins]], [[peregrine falcon]]s, and [[sharp-shinned hawk]]s. While evasive flight is the usual response to predators in free-flying swallows, mobbing behavior is common around the nest,<ref name= Winkler/> and is directed not just towards predators, but also towards nest site competitors, who might be scared off by it.<ref name="Winkler1992"/> This behavior involves the swallow swarming and diving towards (but not actually striking) the intruder<ref name= Winkler/> from around {{convert|5|to|20|m|ft|abbr=on}} above the ground, usually giving soft ticking calls near the end and coming within about {{convert|0.5|to|2|m|ft|abbr=on}} of the predator.<ref name="Winkler1992"/> It seems to alter the intensity of its attacks based on which predator approaches;<ref name= Winkler/> a 1992 study found that ferrets elicited a more vigorous defense than black rat snakes,<ref name="Winkler1992"/> and a 2019 thesis similarly discovered that black rat snake models were dived at the least and [[eastern chipmunk]] models the most.<ref name="Maass2019">{{cite thesis|last=Maass|first=Natalia May|title=Perceived predation risk and the responses of adult and nestling tree swallows (''Tachycineta bicolor'')|year=2019|type=[[Master of Science|MS]]|publisher=[[Eastern Kentucky University]]}}</ref> It is suggested that the snake prompted a weaker response because defense behaviors may be less effective<ref name="Winkler1992"/> and more dangerous to perform against it.<ref name="Maass2019"/>

===Parasites===
[[File:Protocalliphora azurea ? (35372959113).jpg|thumb|Blow-fly in the genus ''Protocalliphora'']]
The tree swallow is vulnerable to various parasites, such as the blood parasite ''[[Trypanosoma]]''. It is also susceptible to the flea ''[[Ceratophyllus idius]]'' and the feather mites ''[[Pteronyssoides tyrrelli]]'', ''[[Trouessartia]]'', and (likely) ''[[Hemialges]]''. It is also probably afflicted by lice of the genera ''[[Brueelia]]'' and ''[[Myrsidea]]''. There is a correlation between the number of fleas on a bird and the number of young it is caring for. This relationship is speculated to arise from an improved microclimate for fleas due to a larger clutch.<ref name="ShutlerMullie2004">{{cite journal|last1=Shutler|first1=Dave|last2=Mullie|first2=Adele|last3=Clark|first3=Robert G|title=Tree swallow reproductive investment, stress, and parasites|journal=Canadian Journal of Zoology|volume=82|issue=3|year=2004|pages=442–448|issn=0008-4301|doi=10.1139/z04-016|bibcode=2004CaJZ...82..442S |citeseerx=10.1.1.530.1736}}</ref> Nestlings also suffer from parasites, like [[blow-fly|blow-flies]] of the genus ''[[Protocalliphora]]'',<ref name="RobyBrink1992"/> which results in a loss of blood by nestlings.<ref name="DeSimoneClotfelter2018">{{cite journal|last1=DeSimone|first1=Joely G.|last2=Clotfelter|first2=Ethan D.|last3=Black|first3=Elizabeth C.|last4=Knutie|first4=Sarah A.|title=Avoidance, tolerance, and resistance to ectoparasites in nestling and adult tree swallows|journal=Journal of Avian Biology|volume=49|issue=2|year=2018|pages=jav–01641|issn=0908-8857|doi=10.1111/jav.01641}}</ref> These parasites, though, are found in a majority of nests and do not seem to have a large effect on nestlings. A study published in 1992 found that the effects of blow-fly parasitism explained only about 5.5% of the variation in nestling mass.<ref name="RobyBrink1992">{{cite journal|last1=Roby|first1=Daniel D.|last2=Brink|first2=Karen L.|last3=Wittmann|first3=Karin|title=Effects of bird blowfly parasitism on eastern bluebird and tree swallow nestlings|journal=Wilson Bulletin|year=1992|volume=104|issue=4|pages=630–643|url=http://sora.unm.edu/sites/default/files/journals/wilson/v104n04/p0630-p0643.pdf}}</ref>

===Immunology===
In the breeding female tree swallow, humoral [[immunocompetence]] (HIC) is inversely correlated with laying date. This means that, on average, a bird that lays its eggs earlier has a stronger antibiotic response to an [[antigen]] than a bird that lays later. A tree swallow that is handicapped by wing-clipping generally has a lower HIC. These relationships could be interpreted as supporting the conclusion that a female that lays earlier acquires a higher HIC, but the authors of the study that found the correlations believed this unlikely, due to the colder temperatures near the start of the breeding season. Instead, they thought that HIC could be a measure of quality, and that a higher quality female is able to lay earlier. The authors also postulated that it is an indicator of workload, as shown by the lower HIC of handicapped birds.<ref name="HasselquistWasson2001">{{cite journal|last1=Hasselquist|first1=Dennis|last2=Wasson|first2=Matthew F.|last3=Winkler|first3=David W.|title=Humoral immunocompetence correlates with date of egg-laying and reflects work load in female tree swallows|journal=Behavioral Ecology|volume=12|issue=1|year=2001|pages=93–97|issn=1465-7279|doi=10.1093/oxfordjournals.beheco.a000384|doi-access=free}}</ref>

Higher quality female tree swallows (as measured by laying date) are able to maintain their reproductive effort while diverting resources to fight an immune challenge. Lower quality swallows are less able to do so; a 2005 study in Ithaca, New York, found that late-laying females with an artificially enlarged brood, although able to maintain offspring quality, had lower responses to an immune challenge than those that were of higher quality or did not have an enlarged brood.<ref name="Ardia2005a">{{cite journal|last1=Ardia|first1=Daniel R.|title=Individual quality mediates trade-offs between reproductive effort and immune function in tree swallows|journal=Journal of Animal Ecology|volume=74|issue=3|year=2005|pages=517–524|issn=0021-8790|doi=10.1111/j.1365-2656.2005.00950.x|doi-access=free|bibcode=2005JAnEc..74..517A }}</ref> Whether a female chooses to prioritize offspring quality or immunocompetence is likely related to survival probabilities; a 2005 study discovered that females with an enlarged brood in Alaska, where survival rates are lower, had weaker immune responses, but kept reproductive effort steady, whereas those in Tennessee, with higher survival rates, had a stronger response but lower quality offspring.<ref name="Ardia2005b">{{cite journal|last1=Ardia|first1=Daniel R.|title=Tree swallows trade off immune function and reproductive effort differently across their range|journal=Ecology|volume=86|issue=8|year=2005|pages=2040–2046|issn=0012-9658|doi=10.1890/04-1619|bibcode=2005Ecol...86.2040A |s2cid=33354318}}</ref>

In the tree swallow, some components of the immune system deteriorate with age. Acquired [[T cell]]-mediated immunity, for example, declines with age in the female tree swallow. But, the age of a female does not affect both the acquired and innate [[humoral immunity]]; the lack of deterioration in the former contrasts with studies on [[barn swallow]]s and female [[collared flycatcher]]s.<ref name="PalaciosCunnick2007">{{cite journal|last1=Palacios|first1=Maria G|last2=Cunnick|first2=Joan E|last3=Winkler|first3=David W|last4=Vleck|first4=Carol M|title=Immunosenescence in some but not all immune components in a free-living vertebrate, the tree swallow|journal=Proceedings of the Royal Society B: Biological Sciences|volume=274|issue=1612|year=2007|pages=951–957|issn=0962-8452|doi=10.1098/rspb.2006.0192|pmid=17251097|pmc=2141670}}</ref> Because of this immunosenescence (a decrease in immune function with age), older females infected with a disease generally visit their nest less, resulting in their nestlings growing slower. They are also likely to lose weight because of an infection.<ref name="PalaciosWinkler2011">{{cite journal|last1=Palacios|first1=Maria G.|last2=Winkler|first2=David W.|last3=Klasing|first3=Kirk C.|last4=Hasselquist|first4=Dennis|last5=Vleck|first5=Carol M.|title=Consequences of immune system aging in nature: a study of immunosenescence costs in free-living tree swallows|journal=Ecology|volume=92|issue=4|year=2011|pages=952–966|issn=0012-9658|doi=10.1890/10-0662.1|pmid=21661557|bibcode=2011Ecol...92..952P |url=http://lib.dr.iastate.edu/eeob_las_pubs/5|type=Submitted manuscript}}</ref>