Editing Tree swallow (section)

===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>