Song birds are shrinking

Bergmann’s rule posits that populations and species of larger sizes are found in colder regions while in warmer regions species are smaller.

A study published yesterday in the Journal Ecology Letters reports that over the pervious four decades there has been, on average, a 2.4 percent decrease in the size of the length of the tarsus bone, a standard marker for bird size,  in a sample population of over 70,000 birds from 52 species. The changes in tarsus length were correlated with the increase temperature. The lead authors of the study suggested two explanations for the decrease in body size.

“The first is developmental plasticity, in which individuals that mature in warmer temperatures tend to develop into smaller adults,” Weeks explained. “The second is natural selection, in which smaller birds tend to do better — in survival, reproduction, or both — in warmer temperatures, leading to a shift in the average size of individuals in a population.”

In addition, the study found consistent increases in the wing length of 1.3 percent in 40 of the species. The reason for in increase in wing length is unclear  but the authors hypothesized that increasing wing length may represent a compensatory adaptation to maintain migration as reductions in body size have increased the metabolic cost of flight. Like many of the consequences of climate change, the changes measured in bird size, are not perceptible to the naked eye.

There is a good summary of the study here by the Audubon society.

Click any image for slide show.


Western Grebe


We usually do not see Grebes on the local pond during winter in our neck of the woods. However, last week, this Western Grebe was swimming in a small section of a local pond that remained unfrozen. Perhaps she if off course in migration and landed here to rest and refuel. Although it was a pleasure to see her, I hope she takes advantage of this weeks thaw to get back on track and is gone the next time I visit this pond.

New Discoveries

First sighted by birders in the lowland forests of Borneo  over a decade ago the Spectacled Flowerpecker has now been studied and classified as a new species. The species was studied by Chris Milensky and Jacob Saucier from the Smithsonian’s National Museum of Natural History while conducting a bird diversity survey. A specimen was captured in the groups mistnet enabling the scientists to collect a DNA sample and confirm that the bird is genetically distant from other known species of flowerpeckers. It is the first new bird species to be found in Borneo for 100 years and a reminder that there are still discoveries to be made.

A quote from Milensky is also a reminder that while there are indeed innumerable scientific discoveries to be made what enables these discoveries is intact habitat for species to exist.

“the discovery of the Spectacled Flowerpecker reflects the boundless biodiversity of the Bornean forests. “Birds are pretty well-studied compared to other organisms, so whenever you find a new bird, you realize just how little you know. Who knows how many insects and invertebrates and other things are still left to be discovered in these forests?” he says. “There are so many other organisms out there that we certainly don’t even know about, that really do require habitat preservation.” 


1.  Jacob R. Saucier, Christopher M. Milensky, Marcos A. Caraballo-Ortiz, Roslina Ragai, N. Faridah Dahlan, David P. Edwards. A distinctive new species of flowerpecker (Passeriformes: Dicaeidae) from Borneo. Zootaxa, 2019; 4686 (4): 451 DOI: 10.11646/zootaxa.4686.4.1