An analysis of 3,463 rabbit and hare bones – spanning 10 millennia – break when wood rabbit and hares were doing that for which they ’re best known : genteelness . Bunny booms occurred when prehistoric El Niño climate effect drenched the Pacific Coast with hard rainfall , encouraging the growth of delectable plants .
The complex weather patternEl Niñotraditionally relate to a lovesome ocean current that appears off the coast of equatorial South America just after Christmas . It come every two to 10 years , and when it does , Mexico ’s Baja California is inundated . “ There were n’t many El Niños from 10,000 to 5,000 years ago , ” perhaps between zero and two per C , University of Utah ’s Jack Broughtonexplains . “ After 5,000 years ago , there was a relatively spectacular gain in frequency of El Niños in Baja , and the coney go through the cap . ”
Broughton and colleagues separated thousands of bunny girl bone from more than a million other humble animal bits collected from an sea - side rock outcrop 150 kilometers ( 95 stat mi ) in the south of Tijuana , Mexico . It was called Abrigo de los Escorpiones , or Shelter of the Scorpions ( pictured below ) , and it ’s where raptors like hawk and bird of Jove would sit and wipe out their prey . The bones would just fall to the bottom of the cliff . Researchers collected 15 boxes worth of bones – from birds to gopher to woodrats – that had accumulated over the course of 10,000 years .
By compare skull and jaw measurements with museum specimens , the squad name three Baja bunny specie : the brush rabbit ( genus Sylvilagus bachmani ) , the desert cottontail ( genus Sylvilagus audubonii ) , and the black - tailed jackrabbit ( Lepus californicus ) . Brush rabbit eat Gunter Wilhelm Grass and forbs near obtuse copse , and they thrive when there ’s more wet ; the desert cottontail has a similar dieting but tolerates drier , more opened weather condition . ironical - do it jackrabbit , on the other hand , opt sparse vegetation . Because there ’s no lineal record of ancient El Niños at the internet site , the squad turned to Ecuadoran lake deposits .
The bit of El Niños per century “ correlate very powerfully with the total rabbit universe in Baja California , as well as comparative teemingness of the moisture - loving species , ” saysUniversity of Utah ’s Isaac Hart . That is , more brush rabbits , cottontail , and jackrabbits , in that order . moreover , warmer eastern Pacific ocean think of more unfused , juvenile bunny girl osseous tissue comparative to fused , adult ones . Bunny copiousness overburden !
Most work on long - full term trend in little westerly North American mammals focus on upcountry sites where temperature heavily influenced their populations over the last 10 millennia . “ This subject field is the most detailed of a coastal site over such a long period of time , and it establish haste is the dominant broker , ” Broughton explain . Compared to the home , coastal rabbits and hares are less harmed by temperature changes because the Pacific Ocean has a temperature - improve impression . “ The longer disc we ’ve provide here , ” he adds , “ should in the end give up us to better presage how El Niño will vary in the time to come , and how animal universe will change as a result . "
The finding will be release in anupcoming issueofQuaternary Research .
range : Lee J. Siegel ( top ) , Isaac Hart ( middle ) / University of Utah
