Editing Blue whale (section)

==Behavior and ecology==
[[File:Bluewhale1 noaa crop.jpg|right|thumb|alt=Photograph of a whale blowing |The blow of a blue whale]]
The blue whale is usually solitary, but can be found in pairs. When productivity is high enough, blue whales can be seen in gatherings of more than 50 individuals.<ref name=Sears_Perr_2009/> Populations may go on long [[Animal migration|migrations]], traveling to their summer feeding grounds towards the poles and then heading to their winter breeding grounds in more equatorial waters.<ref name=NOAAblue>{{cite web|url=https://www.fisheries.noaa.gov/species/blue-whale#overview | title=Blue Whale | publisher=NOAA Fisheries | access-date= 11 November 2019}}</ref> The animals appear to use memory to locate the best feeding areas.<ref>{{cite journal|author1=Abrahms, B.|author2=Hazen, E. L.|author3=Aikens, E. O.|author4=Savoca, M. S.|author5=Goldbogen, J. A.|author6=Goldbogen, S. J.|author7=Jacox, M. G.|author8=Irvine, L. M.|author9=Palacios, D. M.|author10=Mate, B. R.|year=2019|title=Memory and resource tracking drive blue whale migrations|journal=Proceedings of the National Academy of Sciences|volume=116|issue=12|pages=5582–5587|doi=10.1073/pnas.1819031116| pmid=30804188 | pmc=6431148 |bibcode=2019PNAS..116.5582A | doi-access=free }}</ref> There is evidence of alternative strategies, such as year-round residency, and partial (where only some individuals migrate) or age/sex-based migration. Some whales have been recorded feeding in breeding grounds.<ref name=Geijer_etal_2016>{{cite journal | author1=Geijer, C. K. | author2=Notarbartolo di Sciara, G. | author3=Panigada, S. | title=Mysticete migration revisited: Are Mediterranean fin whales an anomaly? | journal=Mammal Review | volume=46 | issue=4 | pages=284–296 | date=2016| doi=10.1111/mam.12069 }}</ref> Blue whale typically swim at {{convert|2|–|8|km/h|sp=us}} but may swim faster at {{convert|32|–|36|km/h|sp=us}} during encounters with boats, predators or other individuals.<ref>{{cite web |last1=EEN|first1=BREIWICK|title=Blue Whale (Balaenoptera musculus)|page=13|url=https://www.sararegistry.gc.ca/virtual_sara/files/cosewic/sr_blue_whale_e.pdf|access-date=24 February 2025}}</ref> Their massive size limits their ability to [[Cetacean surfacing behaviour#Breaching and lunging|breach]].<ref>{{cite journal|author1=Segre, P. S.|author2=Potvin, J|author3=Cade, D. E.|author4=Calambokidis, J|author5=Di Clemente , J|author6=Fish, F. E.|author7=Friedlaender, A. S.|author8=Gough, W. T.|author9=Kahane-Rapport, S. R.|author10=Oliveira, C|author11=Parks, S. E.|author12=Penry, G. S.|author13=Simon, M|author14=Stimpert, A. K.|author15=Wiley, D. N.|author16=Bierlich, K. C.|author17=Madsen, P. T.|author18=Goldbogen, J. A.|year=2020|title=Energetic and physical limitations on the breaching performance of large whales|journal=Physics of Living Systems|volume=9 |doi=10.7554/eLife.51760 |pmid=32159511 |pmc=7065846 |doi-access=free }}</ref>

The greatest dive depth reported from tagged blue whales was {{convert|315|m|sp=us}}.<ref name=Goldbogen_etal_2011/> Their theoretical aerobic dive limit was estimated at 31.2 minutes,<ref name=Croll_etal_2001>{{cite journal | author1=Croll, D. A. | author2=Aceveo-Gutierrez, A. | author3=Tershy, B. R. | author4=Urban-Ramirez, J. | title=The diving behavior of blue and fin whales: Is dive duration shorter than expected based on oxygen stores? | journal= Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology| volume=129 | issue=4 | pages=797–809 | date=2010| doi=10.1016/S1095-6433(01)00348-8 | pmid=11440866 }}</ref> however, the longest dive measured was 15.2 minutes.<ref name=Goldbogen_etal_2011/> The deepest confirmed dive from a pygmy blue whale was {{convert|506|m|sp=us}}.<ref name=Owen_etal_2016>{{cite journal | author1=Owen, K. | author2=Jenner, C. S. | author3=Jenner, M.-N. M. | author4=Andrews, R. D. | title=A week in the life of a pygmy blue whale: migratory dive depth overlaps with large vessel drafts | journal=Animal Biotelemetry | volume=4 | issue=17 | pages=1–11 | date=2016 | doi=10.1186/s40317-016-0109-4| doi-access=free | bibcode=2016AnBio...4...17O }}</ref> A blue whale's heart rate can drop to 2 beats per minute (bpm) at deep depths, but upon surfacing, can rise to 37 bpm, which is close to its peak heart rate.<ref>{{cite journal|author1=Goldbogen, J. A.|author2=Cade, D. E.|author3=Calambokidis, J.|author4=Czapanskiy, M. F.|author5=Fahlbusch, J.|author6=Friedlaender, A. S.|author7=Gough, W. T.|author8=Kahane-Rapport, S. R.|author9=Savoca, M. S.|author10=Ponganis, K. V.|author11=Ponganis, P. J.|year=2019|title=Extreme bradycardia and tachycardia in the world's largest animal|journal=Proceedings of the National Academy of Sciences|volume=116|issue=50|pages=25329–25332|doi=10.1073/pnas.1914273116| pmid=31767746 | pmc=6911174 |bibcode=2019PNAS..11625329G | doi-access=free }}</ref>

===Diet and feeding===
[[File:Blue-whale.jpg|thumb|alt=Photograph blue whale near surface with throat bulging | Blue near the surface after feeding]]
The blue whale's diet consists almost exclusively of [[krill]].<ref name=Sears_Perr_2009/> Blue whales capture krill through lunge feeding; they swim towards them at high speeds as they open their mouths up to 80°.<ref name=Sears_Perr_2009/><ref name=Goldbogen_etal_2011/> They may engulf {{convert|220|t|sp=us}} of water at one time.<ref name=Fossette_etal_2017>{{cite journal | author1=Fossette, S. | author2=Abrahms, B. | author3=Hazen, E. L. | author4=Bograd, S. J. | author5=Zilliacus, K. M. | author6=Calambokidis, J. | author7=Burrows, J. A. | author8=Goldbogen, J. A. | author9=Harvey, J. T. | author10=Marinovic, B. | author11=Tershy, B. | author12=Croll, D. A. | title=Resource partitioning facilitates coexistence in sympatric cetaceans in the California Current | journal=[[Ecology and Evolution]] | volume=7 | issue=1 | pages=9085–9097 | date=2017| doi=10.1002/ece3.3409 | pmid=29152200 | pmc=5677487 | bibcode=2017EcoEv...7.9085F }}</ref> They squeeze the water out through their baleen plates with pressure from the throat pouch and tongue, and swallow the remaining krill.<ref name=Sears_Perr_2009/><ref name=Goldbogen_etal_2011>{{cite journal | author1=Goldbogen, J. A. | author2=Calambokidis, J. | author3=Oleson, E. | author4=Potvin, J.|author5-link=Nicholas Pyenson | author5=Pyenson, N. D. | author6=Schorr, G. | author7=Shadwick, R. E. | title=Mechanics, hydrodynamics and energetics of blue whale lunge feeding: Efficiency dependence on krill density | journal=Journal of Experimental Biology | volume=214 | issue=1 | pages=131–46 | date=2011| doi=10.1242/jeb.048157 | pmid=21147977 | doi-access=free | bibcode=2011JExpB.214..131G }}</ref> Blue whales have been recorded making 180° rolls during lunge-feeding, possibly allowing them to search the prey field and find the densest patches.<ref name=Goldbogen_etal_2012>{{cite journal | author1=Goldbogen, J. A. | author2=Calambokidis, J. | author3=Friedlaender, A. S. | author4=Francis, J. | author5=DeRuiter, A. L. | author6=Stimpert, A. K. | author7=Falcone, E. | author8=Southall, B. L. | title=Underwater acrobatics by the world's largest predator: 360° rolling manoeuvres by lunge-feeding blue whales | journal=[[Biology Letters]] | volume=9 | issue=1 | doi=10.1098/rsbl.2012.0986 | pmid=23193050 | pmc=3565519 | page=20120986 | date=2012}}</ref>

While pursuing krill patches, blue whales maximize their calorie intake by increasing the number of lunges while selecting the thickest patches. This provides them enough energy for everyday activities while storing additional energy necessary for migration and reproduction. Due to their size, blue whales have larger energetic demands than most animals resulting in their need for this specific feeding habit.<ref>{{Cite web |last=Barlow |first=Dawn R. |date=2023 |title=Shaped by their Environment: Variation in Blue Whale Morphology Across Three Productive Coastal Ecosystems |url=https://academic.oup.com/iob/article/5/1/obad039/7438866 |access-date=23 November 2024 |website=Integrative Organismal Biology}}</ref> Blue whales have to engulf densities greater than 100 krill/m<sup>3</sup> to maintain the cost of lunge feeding.<ref name=Goldbogen_etal_2011/><ref name=Hazen_etal_2015>{{cite journal | author1=Hazen, E. L. | author2=Friedlaender, A. S. | author3=Goldbogen, J. A. | title=Blue whales ("Balaenoptera musculus") optimize foraging efficiency by balancing oxygen use and energy gain as a function of prey density | journal=Science Advances | volume=1 | issue=9 | page=e1500469 | date=2015| bibcode=2015SciA....1E0469H | doi=10.1126/sciadv.1500469 | pmid=26601290 | pmc=4646804 | doi-access=free }}</ref> They can consume {{convert|34,776|–|1,912,680|kJ|kcal|sp=us}} from one mouthful of krill, which can provide up to 240 times more energy than used in a single lunge.<ref name=Goldbogen_etal_2011/> It is estimated that an average-sized blue whale must consume {{convert|1,120|±|359|kg|sp=us}} of krill a day.<ref name=Brodie_1975>{{cite journal | author1=Brodie, P. F. | title=Cetacean energetics, an overview of intraspecific size variation | journal=Ecology | volume=56 | issue=1 | pages=152–161 | date=1975| doi=10.2307/1935307 | jstor=1935307 | bibcode=1975Ecol...56..152B }}</ref><ref name=Croll_etal_2006>{{cite book | author1=Croll, D. A. | author2=Kudela, R. | author3=Tershy, B. R. | title=Whales, Whaling and Ocean Ecosystems | chapter=Ecosystem impact of the decline of large whales in the North Pacific | publisher=University of California Press | location=Berkeley, CA | editor1-last=Estes | editor1-first=J. A. | pages=202–214 | date=2006}}</ref>  On average, a blue whale eats {{cvt|4|t|sp=}} each day.<ref name=natgeo/>

In the southern ocean, blue whales feed on [[Antarctic krill]] (''Euphausia superba''). In the South Australia, pygmy blue whales (''B. m. brevicauda'') feeds on ''[[Nyctiphanes australis]]''.<ref name=":1">{{Cite journal |last1=de Vos |first1=Asha |last2=Faux |first2=Cassandra E. |last3=Marthick |first3=James |last4=Dickinson |first4=Joanne |last5=Jarman |first5=Simon N. |date=6 April 2018 |title=New Determination of Prey and Parasite Species for Northern Indian Ocean Blue Whales |journal=Frontiers in Marine Science |language=English |volume=5 |doi=10.3389/fmars.2018.00104 |doi-access=free |issn=2296-7745}}</ref> In California, they feed mostly on ''[[Thysanoessa spinifera]],'' but also less commonly on North pacific krill (''[[Euphausia pacifica]]'').<ref>{{Cite journal |last1=Fiedler |first1=Paul C. |last2=Reilly |first2=Stephen B. |last3=Hewitt |first3=Roger P. |last4=Demer |first4=David |last5=Philbrick |first5=Valerie A. |last6=Smith |first6=Susan |last7=Armstrong |first7=Wesley |last8=Croll |first8=Donald A. |last9=Tershy |first9=Bernie R. |last10=Mate |first10=Bruce R. |date=1 August 1998 |title=Blue whale habitat and prey in the California Channel Islands |url=https://www.sciencedirect.com/science/article/abs/pii/S0967064598800179 |journal=Deep Sea Research Part II: Topical Studies in Oceanography |volume=45 |issue=8 |pages=1781–1801 |doi=10.1016/S0967-0645(98)80017-9 |bibcode=1998DSRII..45.1781F |issn=0967-0645}}</ref> Research of the Eastern North Pacific population shows that when diving to feed on krill, the whales reach an average depth of 201 meters, with dives lasting 9.8 minutes on average.<ref name=":1" />

While most blue whales feed almost exclusively on krill, the Northern Indian Ocean subspecies (''B. m. indica'') instead feeds predominantly on [[Sergestidae|sergestid]] shrimp. To do so, they dive deeper and for longer periods of time than blue whales in other regions of the world, with dives of 10.7 minutes on average, and a hypothesized dive depth of about 300 meters. Fecal analysis also found the presence of fish, krill, [[Amphipoda|amphipods]], [[cephalopod]]s, and [[Scyphozoa|scyphozoan jellyfish]] in their diet.<ref name=":1" />

Blue whales appear to avoid directly competing with other baleen whales.<ref name=Hardin_1960>{{cite journal | author1=Hardin, G. | s2cid=18542809 | title=The competitive exclusion principle | journal=Science | volume=131 | issue=3409 | pages=1292–1297 | date=1960| doi=10.1126/science.131.3409.1292 | pmid=14399717 | bibcode=1960Sci...131.1292H }}</ref><ref name=Hutchinson_1961>{{cite journal | author1=Hutchinson, G. E. | s2cid=86353285 | title=The Paradox of the Plankton | journal=[[The American Naturalist]] | volume=95 | issue=882 | pages=137–145 | date=1961| doi=10.1086/282171 | bibcode=1961ANat...95..137H }}</ref><ref name=Pianka_1974>{{cite journal | author1=Pianka, E. R. | title=Niche overlap and diffuse competition | journal=Proceedings of the National Academy of Sciences | volume=71 | issue=5 | pages=2141–2145 | date=1974| doi=10.1073/pnas.71.5.2141 | pmid=4525324 | pmc=388403 | bibcode=1974PNAS...71.2141P | doi-access=free }}</ref> Different whale species select different feeding spaces and times as well as different prey species.<ref name=Fossette_etal_2017/><ref name=Doniol-Valcroze_2008>{{cite thesis | author1=Doniol-Valcroze, T. | title=Habitat selection and niche characteristics of rorqual whales in the northern Gulf of St. Lawrence (Canada) | type=PhD | publisher=[[McGill University]] | location=Montreal, Canada | date=2008}}</ref><ref name=Friedlaender_etal_2015>{{cite journal | author1=Friedlaender, A. S. | author2=Goldbogen, J. A. | author3=Hazen, E. L. | author4=Calambokidis, J. | author5=Southall, B. L. | title=Feeding performance by sympatric blue and fin whales exploiting a common prey resource | journal=Marine Mammal Science | volume=31 | issue=1 | pages=345–354 | date=2015| doi=10.1111/mms.12134 | bibcode=2015MMamS..31..345F }}</ref> In the [[Southern Ocean]], baleen whales appear to feed on [[Antarctic krill]] of different sizes, which may lessen competition between them.<ref name=Santora_etal_2010>{{cite journal | author1=Santora, J. A. | author2=Reiss, C. S. | author3=Loeb, V. J. | author4=Veit, R. R. | title=Spatial association between hotspots of baleen whales and demographic patterns of Antarctic krill ''Euphausia superba'' suggests size-dependent predation | journal=Marine Ecology Progress Series | volume=405 | pages=255–269 | date=2010| doi=10.3354/meps08513 | bibcode=2010MEPS..405..255S | doi-access=free }}</ref>

Blue whale feeding habits may differ due to situational disturbances, like environmental shifts or human interference. This can cause a change in diet due to stress response. Due to these changing situations, there was a study performed on blue whales measuring cortisol levels and comparing them with the levels of stressed individuals, it gave a closer look to the reasoning behind their diet and behavioral changes.<ref>{{Cite web |last=Melica |first=Valentina |date=2020 |title=Reproduction and Stress Response Endocrinology in Blue (Balaenoptera musculus) and Gray (Eschrichtius robust) Whales |url=https://scholarworks.alaska.edu/bitstream/handle/11122/12414/Melica_V_2020.pdf |access-date=23 November 2024 |website=Scholarworks Alaska}}</ref>

===Reproduction and birth===
[[File:BlueWhaleWithCalf.jpg|thumb|alt=Photograph of a blue whale calf and its mother | A blue whale calf with its mother]]
The age of sexual maturity for blue whales is thought to be 5–15 years.<ref>{{cite web |last1=JM|first1=BREIWICK|title=The Blue Whale,|page=17|url=https://spo.nmfs.noaa.gov/sites/default/files/pdf-content/MFR/mfr464/mfr4644.pdf|access-date=23 February 2025}}</ref> In the Northern Hemisphere, the length at which they reach maturity is {{convert|21|–|23|m|sp=us}} for females and {{convert|20|–|21|m|sp=us}} for males. In the Southern Hemisphere, the length of maturity is {{convert|23|–|24|m|sp=us}} and {{convert|22|m|sp=us}} for females and males respectively.<ref name=Sears_Perrin_2018>{{cite book | author1=Sears, R. | author2=Perrin, W. F. | title=Encyclopedia of marine mammals | chapter=Blue Whale: "Balaenoptera musculus" | publisher=Academic Press | location=London, UK | editor1-last=Würsig | editor1-first=B. | editor2-last=Thewissen | editor2-first=J. G. M. | editor3-last=Kovacs | editor3-first=K. M. | pages=110–114 | date=2018}}</ref> Male pygmy blue whales average {{convert|61.4|ft|order=flip|sp=us}} at sexual maturity.<ref name=Ichihara_1964>{{cite journal | author1=Ichihara T. | title=The pygmy blue whale, ''Balaenoptera musculus brevicauda'', a new subspecies from Antarctic | journal=Norsk. Hvalf. Tid. | volume=6 | date=1964}}</ref><ref name=Sazhinov_1970>{{cite journal | author1=Sazhinov E. G. | title=The onset of sexual and physical maturity for pygmy blue whales (''Balaenoptera musculus brevicauda''. Ichinara. 1966) | journal=Whales of the Southern Hemisphere | issue=29 | pages=34–40 | date=1970}}</ref> Female pygmy blue whales are {{convert|68.9|–|71.2|ft|order=flip|sp=us}} in length<ref name=Branch_2007a/> and roughly 10 years old at the age of sexual maturity.<ref name=Branch_2007a/><ref name=Gilpatrick_Perryman_2008/><ref name=Branch_Mikhalev_2008>{{cite journal | author1=Branch, T. A. | author2=Mikhalev, Y. A. | title=Regional differences in length at sexual maturity for female blue whales based on recovered Soviet whaling data | journal=Marine Mammal Science | volume=24 | issue=3 | pages=690–703 | date=2008| doi=10.1111/j.1748-7692.2008.00214.x | bibcode=2008MMamS..24..690B }}</ref> Since corpora are added every ~2.5 years after sexual maturity, physical maturity is assumed to occur at 35 years.<ref>{{cite web |title=Sex ratios in blue whales from conception onward|page=23|url=https://repository.library.noaa.gov/view/noaa/63149/noaa_63149_DS1.pdf|access-date=7 February 2025}}</ref> Little is known about mating behavior, or breeding and birthing areas.<ref name=Mizroch_1984/><ref name=Sears_Perrin_2018/> Blue whales appear to be [[Polygyny in animals|polygynous]], with males competing for females.<ref name=Sears_Perrin_2018/><ref name=Sears_etal_2013>{{cite journal | author1=Sears, R. | author2=Ramp, C. | author3=Douglas, A. B. | author4=Calambokidis, J. | title=Reproductive parameters of eastern North Pacific blue whales ''Balaenoptera musculus'' | journal=Endangered Species Research | volume=22 | issue=1 | pages=23–31 | date=2013| doi=10.3354/esr00532 | doi-access=free }}</ref> A male blue whale typically trails a female and will fight off potential rivals.<ref name=Schall_etal_2019>{{cite journal | author1=Schall, E. | author2=Di Lorio, L. | author3=Berchok, C. | author4=Filún, D. | author5=Bedriñana-Romano, L. | author6=Buchan, S. J. | author7=Van Opzeeland, I. | author8=Sears, R. | author9=Hucke-Gaete, R. | title=Visual and passive acoustic observations of blue whale trios from two distinct populations | journal=Marine Mammal Science | volume=36 | issue=1 | doi=10.1111/mms.12643 | pages=365–374 | date=2019| doi-access=free | hdl=1912/24953 | hdl-access=free }}</ref> The species mates from fall to winter.<ref name=Mizroch_1984/><ref name=Sears_Perrin_2018/>

Pregnant females eat roughly four percent of their body weight daily,<ref name=Sergeant_1969>{{cite journal | author1=Sergeant, D. E. | title=Feeding rates of Cetacea | journal=Fiskeridir. SKR. Havundersok | volume=15 | pages=246–258 | date=1969}}</ref> amounting to 60% of their overall body weight throughout summer foraging periods.<ref name=Sears_Perrin_2018/><ref name=Lockyer_1984b>{{cite journal | author1=Lockyer, C. | title=Review of baleen whale (Mysticeti) reproduction and implications for management | journal=Report of the International Whaling Commission | volume=6 | pages=27–50 | date=1984}}</ref> [[Gestation]] may last 10–12 months with calves being {{convert|6|–|7|m|sp=us}} long and weighing {{convert|2|–|3|t|sp=us}} at birth.<ref name=Sears_Perrin_2018/> Estimates suggest that because calves require {{convert|2|-|4|kg|sp=us}} milk per kg of mass gain, blue whales likely produce {{convert|220|kg|sp=us}} of milk per day (ranging from {{convert|110|to|320|kg|sp=us}} of milk per day).<ref name=Oftedal_1997>{{cite journal | author1=Oftedal, O. T. | s2cid=19588882 | title=Lactation in whales and dolphins: Evidence of divergence between baleen- and toothed-species | journal=Journal of Mammary Gland Biology and Neoplasia | volume=2 | issue=3 | pages=205–230 | date=1997| doi=10.1023/A:1026328203526 | pmid=10882306 }}</ref> The first video of a calf thought to be nursing was filmed in New Zealand in 2016.<ref>{{cite web | url=https://www.nationalgeographic.com/news/2016/03/160302-blue-whale-mother-calf-nursing-video-pygmy-new-zealand/ | archive-url=https://web.archive.org/web/20191231040656/https://www.nationalgeographic.com/news/2016/03/160302-blue-whale-mother-calf-nursing-video-pygmy-new-zealand/ | url-status=dead | archive-date=31 December 2019 | title=Exclusive Video May Show Blue Whale Calf Nursing | date=2 March 2016 | publisher=[[National Geographic]] | access-date=20 December 2019}}</ref> Calves may be [[weaned]] when they reach 6–8 months old at a length of {{convert|53|ft|order=flip|sp=us}}.<ref name=Sears_Perrin_2018/> They gain roughly {{convert|37,500|lb|sp=us}} during the weaning period.<ref name=Lockyer_1981/> Interbirth periods last two to three years;<ref name=Sears_Perrin_2018/> they average 2.6 years in pygmy blue whales.<ref name=Branch_2008/> Mother-calf pairings are infrequently observed, and this may be due to mothers birthing and weaning their young in-between their entry and return to their summer feeding grounds.<ref>{{cite journal|last=Branch|first=T. A.|year=2025|title=Timing hypothesis explains the mystery of the missing blue whale calves|journal=Endangered Species Research|volume=56|pages=53–67|doi=10.3354/esr01383|doi-access=free}}</ref>

===Vocalizations===
{{listen
 | pos          = right
 | filename     = Blue whale atlantic1.ogg
 | title        = A blue whale song
 | description  = Recorded in the Atlantic (1)
 | format       = [[Ogg]]
 | filename2    = Blue whale atlantic3.ogg
 | title2       = A blue whale song
 | description2 = Recorded in the Atlantic (2)
 | format2      = [[Ogg]]
 | filename3    = Blue_Whale_NE_Pacific.ogg
 | title3       = A blue whale song
 | description3 = Recorded in North Eastern Pacific
 | format3      = [[Ogg]]
 | filename4    = Blue_Whale_South_Pacific.ogg
 | title4       = A blue whale song
 | description4 = Recorded in the South Pacific
 | format4      = [[Ogg]]
 | filename5    = Blue_Whale_West_Pacific.ogg
 | title5       = A blue whale song
 | description5 = Recorded in the West Pacific
 | format5      = [[Ogg]]
}}
Blue whales produce some of the loudest and lowest [[frequency]] vocalizations in the animal kingdom,<ref name=NOAA/> and their inner ears appear well adapted for detecting [[Low frequency|low-frequency]] sounds.<ref name=Yamato_etal_2008>{{cite journal | author1=Yamato, M. | author2=Ketten, D. R. | author3=Arruda, J. | author4=Cramer, S. | title=Biomechanical and structural modeling of hearing in baleen whales | journal=Bioacoustics | volume=17 | issue=1–3 | pages=100–102 | date=2008| doi=10.1080/09524622.2008.9753781 | bibcode=2008Bioac..17..100Y | s2cid=85314872 }}</ref> The [[fundamental frequency]] for blue whale [[Animal communication#Auditory|vocalizations]] ranges from 8 to 25&nbsp;Hz.<ref name=Stafford_etal_1998>{{cite journal | author1=Stafford, K. M. | author2=Fox, G. C. | author3=Clark, D. S. | title=Long-range acoustic detection and localization of blue whale calls in the northeast Pacific Ocean | journal=Journal of the Acoustical Society of America | volume=50 | issue=4 | pages=1193–1198 | date=1998| bibcode=1998ASAJ..104.3616S | doi=10.1121/1.423944 | pmid=9857519 }}</ref> Blue whale songs vary between populations.<ref name=McDonald_etal_2006>{{cite journal | author1=McDonald, M. A. | author2=Mesnick, S. L. | author3=Hildebrand, J. A. | title=Biogeographic characterization of blue whale song worldwide: Using song to identify populations | journal=Journal of Cetacean Research and Management | volume=8 | pages=55–66 | date=2023| doi=10.47536/jcrm.v8i1.702 | s2cid=18769917 | doi-access=free }}</ref>

Vocalizations produced by the Eastern North Pacific population have been well studied. This population produces pulsed calls ("A") and tonal calls ("B"), upswept tones that precede type B calls ("C") and separate downswept tones ("D").<ref name=Aroyan_etal_2000>{{cite book | author1=Aroyan, J. L. | author2=McDonald, M. A. | author3=Webb, S. C. | author4=Hildebrand, J. A. | author5=Clark, D. S. | author6=Laitman, J. T. | author7=Reidenberg, J. S. | title=Hearing by whales and dolphins | chapter=Acoustic models of sound production and propagation | editor1-last=Au | editor1-first=W. W. A. | editor2-last=Popper | editor2-first=A. | editor3-last=Fay | editor3-first=R. N. | publisher=Springer-Verlag | location=New York | page=442 | date=2000}}</ref><ref name=McDonald_etal_2001>{{cite journal | author1=McDonald, M. A. | author2=Calambokidis, J. | author3=Teranishi, A. M. | author4=Hildebrand, J. A. | title=The acoustic calls of blue whales off California with gender data | journal=Journal of the Acoustical Society of America | volume=109 | issue=4 | pages=1728–1735 | date=2001| doi=10.1121/1.1353593 | pmid=11325141 | bibcode=2001ASAJ..109.1728M | url=http://www.escholarship.org/uc/item/6vg9t2g7 }}</ref> A and B calls are often produced in repeated co-occurring sequences and sung only by males, suggesting a reproductive function.<ref name=McDonald_etal_2001/><ref name=Oleson_etal_2007a>{{cite journal | author1=Oleson, E. M. | author2=Calambokidis, J. | author3=Burgess, W. C. | author4=McDonald, M. A. | author5=LeDuc, C. A. | author6=Hildebrand, J. A. | title=Behavioral context of call production by eastern North Pacific blue whales | journal= [[Marine Ecology Progress Series]]| volume=330 | pages=269–284 | date=2007| doi=10.3354/meps330269 | bibcode=2007MEPS..330..269O | doi-access=free }}</ref> D calls may have multiple functions. They are produced by both sexes during social interactions while feeding.<ref name=Oleson_etal_2007a/><ref name=Lewis_etal_2018>{{cite journal | author1=Lewis, L. A. | author2=Calambokidis, J. | author3=Stimpert, A. K. | author4=Fahlbusch, J. | author5=Friedlaender, A. S. | author6=McKenna, M. F. | author7=Mesnick, S. | author8=Oleson, E. M. | author9=Southall, B. L. | author10=Szesciorka, A. S. | author11=Sirovic, A. | title=Context-dependent variability in blue whale acoustic behaviour | journal=[[Royal Society Open Science]] | volume=5 | issue=8 | page=1080241 | date=2018 | doi=10.1098/rsos.180241| pmid=30225013 | pmc=6124089 }}</ref> and by males when competing for mates.<ref name=Schall_etal_2019/>

Blue whale calls recorded off Sri Lanka have a three-unit phrase. The first unit is a 19.8 to 43.5&nbsp;Hz pulsive call, and is normally 17.9 ± 5.2 seconds long. The second unit is a 55.9 to 72.4&nbsp;Hz [[Frequency modulation|FM]] upsweep that is 13.8 ± 1.1 seconds long. The final unit is 28.5 ± 1.6 seconds long with a tone of 108 to 104.7&nbsp;Hz.<ref name=Stafford_etal_2010>{{cite journal | author1=Stafford, K. M. | author2=Chapp, E. | author3=Bohnenstiel, D. | author4=Tolstoy, M. | author4-link=Maya Tolstoy | title=Seasonal detection of three types of "pygmy" blue whale calls in the Indian Ocean | journal=Marine Mammal Science | volume=27 | issue=4 | pages=828–840 | date=2010| doi=10.1111/j.1748-7692.2010.00437.x }}</ref> A blue whale call recorded off Madagascar, a two-unit phrase,<ref name=Ljungblad_etal_1998>{{cite report | author1=Ljungblad, D. K. | author2=Clark, C. W. | author3=Shimada, H. | title=A comparison of sounds attributed to pygmy blue whales (''Balaenoptera musculus brevicauda'') recorded south of the Madagascar Plateau and those attributed to 'true' blue whales (''Balaenoptera musculus'') recorded off Antarctica | publisher=International Whaling Commission | volume=48 | pages=439–442 | date=1998}}</ref> consists of 5–7 pulses with a [[center frequency]] of 35.1 ± 0.7&nbsp;Hz lasting 4.4 ± 0.5 seconds proceeding a 35 ± 0&nbsp;Hz tone that is 10.9 ± 1.1 seconds long.<ref name=Stafford_etal_2010/> In the Southern Ocean, blue whales produce 18-second vocals which start with a 9-second-long, 27&nbsp;Hz tone, and then a 1-second downsweep to 19&nbsp;Hz, followed by a downsweep further to 18&nbsp;Hz.<ref name=Sirovic_etal_2004>{{cite journal | author1=Sirovic, A. | author2=Hildebrand, J. A. | author3=Wiggins, S. M. | author4=McDonald, M. A. | author5=Moore, S. E. | author6=Thiele, D. | title=Seasonality of blue and fin whale calls and the influence of sea ice in the Western Antarctic Peninsula | journal=[[Deep Sea Research Part II: Topical Studies in Oceanography]] | volume=51 | issue=17–19 | pages=2327–2344 | date=2004| doi=10.1016/j.dsr2.2004.08.005 | bibcode=2004DSRII..51.2327S }}</ref><ref name=Rankin_etal_2005/> Other vocalizations include 1–4 second long, frequency-modulated calls with a frequency of 80 and 38&nbsp;Hz.<ref name=Rankin_etal_2005>{{cite journal | author1=Rankin, S. | author2=Ljungblad, D. | author3=Clark, C. | author4=Kato, H. | title=Vocalisations of Antarctic blue whales, ''Balaenoptera musculus intermedia'', recorded during the 2001/2002 and 2002/2003 IWC/SOWER circumpolar cruises, Area V, Antarctica | journal=Journal of Cetacean Research and Management | volume=7 | pages=13–20 | date=2023| doi=10.47536/jcrm.v7i1.752 | s2cid=43993242 | doi-access=free }}</ref><ref name=Sirovic_etal_2006>{{cite journal | author1=Sirovic, A. | author2=Hildebrand, J. A. | author3=Thiele, D. | title=Baleen whales in the Scotia Sea in January and February 2003 | journal=Journal of Cetacean Research and Management | volume=8 | pages=161–171 | date=2006| doi=10.47536/jcrm.v8i2.712 | s2cid=251277044 | doi-access=free }}</ref>

There is evidence that some blue whale songs have temporally declined in tonal frequency.<ref name=Nieukirk_etal_2005>{{cite conference | author1=Nieukirk, S. L. | author2=Mellinger, D. K. | author3=Hildebrand, J. A. | author4=McDonald, M. A. | author5=Dziak, R. P. | title=Downward shift in the frequency of blue whale vocalizations | conference=16th Biennial Conference on the Biology of Marine Mammals | location=San Diego, CA | page=205 | date=2005}}</ref><ref name=McDonald_etal_2009>{{cite journal | author1=McDonald, M. A. | author2=Hildebrand, J. A. | author3=Mesnick, S. | title=Worldwide decline in tonal frequencies of blue whale songs | journal=Endangered Species Research | volume=9 | pages=13–21 | date=2009| doi=10.3354/esr00217 | doi-access=free }}</ref><ref name=Leroy_etal_2018>{{cite journal | author1=Leroy, E. C. | author2=Royer, J.-Y. | author3=Bonnel, J. | author4=Samaran, F. | title=Long-term and seasonal changes of large whale call frequency in the southern Indian Ocean | journal=[[Journal of Geophysical Research: Oceans]] | volume=123 | issue=11 | pages=8568–8580 | date=2018| doi=10.1029/2018JC014352 | bibcode=2018JGRC..123.8568L | s2cid=135201588 | url=https://archimer.ifremer.fr/doc/00516/62730/ | doi-access=free | hdl=1912/10837 | hdl-access=free }}</ref> The vocalization of blue whales in the Eastern North Pacific decreased in tonal frequency by 31% from the early 1960s to the early 21st century.<ref name=Nieukirk_etal_2005/><ref name=McDonald_etal_2009/> The frequency of pygmy blue whales in the Antarctic has decreased by a few tenths of a hertz every year starting in 2002.<ref name=Leroy_etal_2018/> It is possible that as blue whale populations recover from whaling, there is increasing sexual selection pressure (i.e., a lower frequency indicates a larger body size).<ref name=McDonald_etal_2009/>

===Predators===
The only known natural predator to blue whales is the [[orca]], although the rate of fatal attacks by orcas is unknown. Photograph-identification studies of blue whales have estimated that a high proportion of the individuals in the [[Gulf of California]] have rake-like scars, indicative of encounters with orcas.<ref name=Sears_1990>{{cite journal | author1=Sears, R. | title=The Cortez blues | journal=Whalewatcher | volume=24 | pages=12–15 | date=1990}}</ref> Off southeastern [[Australia]], 3.7% of blue whales photographed had rake marks and 42.1% of photographed pygmy blue whales off Western Australia had rake marks.<ref name=Mehta_etal_2007>{{cite journal | author1=Mehta, A. V. | author2=Allen, J. M. | author3=Constantine, R. | author4=Garrigue, C. | author5=Jann, B. | author6=Jenner, C. | author7=Marx, M. K. | author8=Matkin, C. O. | author9=Mattila, D. K. | author10=Minton, G. | author11=Mizroch, S. A. | author12=Olavarría, C. | author13=Robbins, J. | author14=Russell, K. G. | author15=Seton, R. E. | title=Baleen whales are not important as prey for orcas (''Orcinus orca'') in high latitudes | journal=Marine Ecology Progress Series | volume=348 | pages=297–307 | date=2007| doi=10.3354/meps07015 | doi-access=free | hdl=1912/4520 | hdl-access=free }}</ref> Documented [[predation]] by orcas has been rare. A blue whale mother and calf were first observed being chased at high speeds by orcas off southeastern Australia.<ref name=Cotton_1944>{{cite journal | author1=Cotton, B. C. | title=Killer whales in South Australia | journal=[[Australian Zoologist]] | volume=10 | pages=293–294 | date=1944}}</ref> The first documented attack occurred in 1977 off southwestern [[Baja California, Mexico]], but the injured whale escaped after five hours.<ref name=Tarpy_1979>{{cite journal | author1=Tarpy, C. | title=Killer whale attack! | journal=National Geographic Magazine | volume=155 | pages=542–545| date=1979}}</ref> Four more blue whales were documented as being chased by a group of orcas between 1982 and 2003.<ref name=Ford_Reeves_2008>{{cite journal | author1=Ford, J. K. B. | author2=Reeves, R. | title=Fight or flight: antipredator strategies of baleen whales | journal=[[Mammal Review]] | volume=38 | issue=1 | pages=50–86 | date=2008| doi=10.1111/j.1365-2907.2008.00118.x }}</ref> The first documented predation event by orcas occurred in September 2003, when a group of orcas in the [[Eastern Tropical Pacific]] was encountered feeding on a recently killed blue whale calf.<ref name=Pitman_etal_2007>{{cite journal | author1=Pitman, R. | author2=Fearnbach, H. | author3=LeDuc, R. | author4=Gilpatrick, J. W. | author5=Ford, J. K. B. | author6=Balance, L. T. | title=Killer whales preying on a blue whale calf on the Costa Rica Dome: Genetics, morphometrics, vocalizations and composition of the group | journal=Journal of Cetacean Research and Management | volume=9 | pages=151–158 | date=2023| issue=2 | doi=10.47536/jcrm.v9i2.683 | s2cid=257138804 | doi-access=free }}</ref> In March 2014, a commercial whale watch boat operator recorded an incident involving a group of orcas harassing a blue whale in [[Monterey Bay]]. The blue whale defended itself by slapping its tail.<ref>{{cite web | url=https://www.livescience.com/43879-killer-whales-attack-blue-whale-video.html | title=Killer Whales Bully Lone Blue Whale in Rare Video | date=5 March 2014 | publisher=[[Live Science]] | access-date=23 December 2019}}</ref> A similar incident was recorded by a drone in Monterey Bay in May 2017.<ref>{{cite web | url=https://www.nationalgeographic.com/news/2017/05/killer-whale-attacks-blue-whale-monterey-drone-video | archive-url=https://web.archive.org/web/20191231040658/https://www.nationalgeographic.com/news/2017/05/killer-whale-attacks-blue-whale-monterey-drone-video/ | url-status=dead | archive-date=31 December 2019 | title=Killer Whales Attacked a Blue Whale—Here's the Surprising Reason Why | date=25 May 2017 | publisher=National Geographic | access-date=23 December 2019}}</ref> The first direct observations of orca predation occurred off the south coast of Western Australia, two in 2019 and one more in 2021. The first victim was estimated to be {{convert|18|–|22|m|sp=us}}.<ref>{{cite journal|author1=Totterdell, J. A.|author2=Wellard, R.|author3=Reeves, I. M.|author4=Elsdon, B.|author5=Markovic, P.|author6=Yoshida, M.|author7=Fairchild, A.|author8=Sharp, G.|author9=Pitman, R.|year=2022|title=The first three records of killer whales (''Orcinus orca'') killing and eating blue whales (''Balaenoptera musculus'')|journal=Marine Mammal Science|volume=38 |issue=3 |pages=1286–1301 |doi=10.1111/mms.12906|bibcode=2022MMamS..38.1286T | s2cid=246167673 }}</ref>

===Infestations and health threats===
In Antarctic waters, blue whales accumulate diatoms of the species ''[[Cocconeis]] ceticola'' and the genera ''[[Navicola]]'', which are normally removed when the whales enter warmer waters. [[Barnacle]]s such as ''[[Coronula diadema]]'', ''[[Coronula reginae]]'', and ''[[Cryptolepas rhachianecti]]'', latch on to whale skin deep enough to leave behind a pit if removed. [[Whale lice]] species make their home in cracks of the skin and are relatively harmless. The [[copepod]] species ''[[Pennella balaenopterae]]'' digs in and attaches itself to the blubber to feed on. Intestinal parasites include the [[trematode]] genera ''[[Ogmogaster]]'' and ''[[Lecithodesmus]]''; the [[tapeworm]] genera ''[[Priapocephalus]]'', ''[[Phyllobotrium]]'', ''[[Tetrabothrius]]'', ''[[Diphyllobotrium]]'', and ''[[Diplogonoporus]]''; and the [[thorny-headed worm]] genus ''[[Bolbosoma]]''. In the North Atlantic, blue whales also contain the protozoans ''[[Entamoeba]]'', ''[[Giardia]]'' and ''[[Balantidium]]''.<ref>{{cite journal|last1=Hermosilla|first1=C|last2=Silva|first2=L. M. R.|last3=Prieto|first3=R|last4=Kleinertz|first4=S|last5=Taubert|first5=A|last6=Silva|first6=M. A.|year=2015|title=Endo- and ectoparasites of large whales (Cetartiodactyla: Balaenopteridae, Physeteridae): Overcoming difficulties in obtaining appropriate samples by non- and minimally-invasive methods|journal=International Journal for Parasitology: Parasites and Wildlife|volume=4|issue=3|pages=414–420|doi=10.1016/j.ijppaw.2015.11.002|pmid=26835249|pmc=4699982|bibcode=2015IJPPW...4..414H}}</ref>