The local news for most of the eastern US and Canada has been aflutter (ha) recently with reports of the irruption of Vanessa atalanta – the Red Admiral butterfly. While this is a common occurrence every spring for these butterflies to migrate north from their overwintering grounds in the southern US, ikaragarriak dira aurtengo kopuru handiak. Literalki milaka almirante daude gure atzeko patioetan.
Beraz, aurten zer den ezberdina?
Udaberriko eguraldi epelaren inguruko espekulazio asko dago (leku askotan izan den martxorik beroena) eta askotan desinformazio asko besaulkiaren entomologiarekin batera joateko. Topatu ditudan albiste-iturri gehienek diote udaberri epelak tximeleta hauei loratzen eta kopuru anormalean ugaltzea ahalbidetu duela.. Hori ez da guztiz posible, ordea, V. atalanta overwinters as an adult. The southern states provide temps just warm enough for adult Vanesa butterflies to hide in the fall and be the very first to awaken in the spring to get a jump start on mating. Otsailean tximeletak esna baziren ere landare ostalariek oraindik ez zeuden (karduak); gure patioetako tximeletak iazkoak dira.
Baina zer gertatuko litzateke eguraldiak zeresana izango balu boom ziklo honetan? Iaz La Niña urtea izan zen gure negu eder eta epelarekin. Aurreko urtean El Niño bat izan zen, most of the eastern US was assaulted with winter and we suffered at the hands of the epic Chicago “snowpocalypse”. Beharbada, konbinazio honek populazio-kopurua nahikoa txikitu zuen 2010/2011 horrek gero karga parasitoidea gutxitu zuen, udan tximeleten ugalkortasun orokor handiagoa ahalbidetuz 2011. Neguko tximeleta horiei negu epela eman zitzaien orduan, neguko hilkortasun txikiagoa ahalbidetu zezakeen. As the butterflies moved north this spring there were no frosty nights to cut into populations – just lots of hungry birds. Ondorioz, tximeleta migratzaileen fluxu anormal bat izango litzateke.
But then again…
Despite butterflies being so popular and well studied there doesn’t seem to be a perfect grip on what conditions each of the Vanesa species prefer. Landare ostalarien aldagaiak, populazio tartea, eguraldiak eta parasitoideek zeregin garrantzitsua dute ugaritasunean eta banaketan. Did the weather cycles of the last few years variably effect one species over another? Nork nahi du doktorego proiektu hori (infernutik)?
One of the best posts I’ve read is by Doug Taron over on Gossamer tapiz – he is skeptical of this warm weather theory. Critically this irruption is effecting only the population of the Red Admiral and any theory involving weather would also likely effect other migrant butterflies like the Vanessa virginiensis – the American Lady. He also points out that an abundant butterfly like the admiral has classic cyclical population booms and busts in sync with parasite populations. I recall another summer in the late 90’s of staggering Admiral populations. Parasites really do better explain what we see in our yards this spring. While the weather might not have caused the abundance of V. atalanta, there can be no denying that butterflies of all species have woken up much earlier this year.
As far as I recall, almost all temperate zone animals (and plants, Susmoa dut) go thru boom and bust cycles. It’s pretty much the function/nature of the wildly variable environmental conditions of the ecosystems. Even the less common temperate zone species cycle but the effects are less noticed simply because of the lower population levels.
must have been a lovely sight, vanessa atlanta has been struggling in the UK for the past few years!!
A few years back you may have heard about the painted lady invasion in the UK very much the same as the USA i was counting well over 1000 an hour coming up the field from the english channel !
Quick question about la nina i believe the later part of 2010 was also la nina thats why the UK and northern USA had such cold weather