Guest essay by Eric Worrall
Birds were amongst the most successful survivors of the Cretaceous-Paleogene extinction event which wiped out the dinosaurs, but researchers claim they won’t be able to cope with the ferocious 1-2C / century pace of the current warming period.
Past climate change pushed birds from the northern hemisphere to the tropics
by University of Cambridge
JUNE 10, 2019
The researchers, from the Universities of Cambridge and Oxford, applied climate and ecological modelling to illustrate how the distribution of major bird groups is linked to climate change over millions of years. However, while past climate change often occurred slowly enough to allow species to adapt or shift habitats, current rates of climate change may be too fast for many species, putting them at risk of extinction. The results are reported in Proceedings of the National Academy of Sciences.
“Palaeontologists have documented long-term links between climate and the geographic distributions of major bird groups, but the computer models needed to quantify this link had not been applied to this question until now,” said Dr. Daniel Field from Cambridge’s Department of Earth Sciences, the paper’s co-lead author.
For the current study, the researchers looked at ten bird groups currently limited to the tropics, predominantly in areas that were once part of the ancient supercontinent of Gondwana (Africa, South America and Australasia). However, early fossil representatives of each of these groups have been found on northern continents, well outside their current ranges.
…Read more: https://phys.org/news/2019-06-climate-birds-northern-hemisphere-tropics.html
The abstract of the study;
Climatic shifts drove major contractions in avian latitudinal distributions throughout the Cenozoic
Erin E. Saupe, Alexander Farnsworth, Daniel J. Lunt, Navjit Sagoo, Karen V. Pham, and Daniel J. Field
Many higher level avian clades are restricted to Earth’s lower latitudes, leading to historical biogeographic reconstructions favoring a Gondwanan origin of crown birds and numerous deep subclades. However, several such “tropical-restricted” clades (TRCs) are represented by stem-lineage fossils well outside the ranges of their closest living relatives, often on northern continents. To assess the drivers of these geographic disjunctions, we combined ecological niche modeling, paleoclimate models, and the early Cenozoic fossil record to examine the influence of climatic change on avian geographic distributions over the last ∼56 million years. By modeling the distribution of suitable habitable area through time, we illustrate that most Paleogene fossil-bearing localities would have been suitable for occupancy by extant TRC representatives when their stem-lineage fossils were deposited. Potentially suitable habitat for these TRCs is inferred to have become progressively restricted toward the tropics throughout the Cenozoic, culminating in relatively narrow circumtropical distributions in the present day. Our results are consistent with coarse-scale niche conservatism at the clade level and support a scenario whereby climate change over geological timescales has largely dictated the geographic distributions of many major avian clades. The distinctive modern bias toward high avian diversity at tropical latitudes for most hierarchical taxonomic levels may therefore represent a relatively recent phenomenon, overprinting a complex biogeographic history of dramatic geographic range shifts driven by Earth’s changing climate, variable persistence, and intercontinental dispersal. Earth’s current climatic trajectory portends a return to a megathermal state, which may dramatically influence the geographic distributions of many range-restricted extant clades.Read more (paywalled): https://www.pnas.org/content/early/2019/06/04/1903866116
Unfortunately the full study is paywalled, but I think we get the idea.
Frankly I don’t buy it. Whatever we’re doing to the climate, the impact of a gigantic meteor which wiped out pretty almost every animal over 55lb probably produced a more abrupt change to global habitats.
Other more recent climate shifts such as the Toba Eruption 75,000 years ago, which may have caused a volcanic winter, were likely a little more abrupt than anything which has occurred in the last few centuries.
I live on the edge of the tropics, I see shifts in bird populations every year – sometimes a few extreme tropics species turn up, then disappear the next year. Sometimes we see the occasional cold climate seagull, but they never stick around.
My point is, birds are always probing the edge of their range. A claim that birds can’t adapt fast enough to survive our gradual modern warming in my opinion is utterly implausible.