Climate change, bird-feeders, evolution, and the importance of long-term data sets

When the climate changes, organisms can respond in just a few possible ways: [1]  change their behavior in their current habitats — for example, plants may flower earlier or retain their leaves longer to accommodate a longer growing season, and birds may change their migration times;  [2] change their ranges — for example, the Carolina wren is now commonly seen in New England, where it was essentially unknown 20 years ago;  [3] the species may evolve in response to changed conditions (or [4] may go extinct_.   

But climate change effects (e.g. more volatile weather, changed precipitation patterns, more frequent high temperatures, less frequent low temperatures)  interact with many other environmental factors, which makes it challenging to establish the relative contribution of these different factors to an observed change in the biology or ecology of an organism.   A recent study by Plummer et al. published in Global Change Biology uses long-term data on the migration of an Old World warbler, the Eurasian blackcap, to understand how changes in climate, and in human bird-feeding behavior, have contributed to the evolution of new migratory behavior in central European blackcaps.

Blackcaps in southern Germany and Austria  (see a brief description and photos here on Wikipedia) historically migrate southwest to the Iberian Peninsula for the winter.  In the past 60 years, however, many  have migrated northwest, to winter in southern and western Great Britain.  The authors cite research that has established that there is a genetic component to this — that is, that this population of blackcaps has evolved in response to the emergence of new winter foraging conditions.

Plummer and her colleagues noted that, while average temperatures have increased over times time, so, too, has the intensity of human bird-feeding in Britain.  They tested their hypothesis that the two factors together could (largely) account for this striking change in migratory patterns, using long-term data sets of several kinds.  They used climatic data, specifically regional changes in average temperature over the study period;  historical records of weather in specific locales within the region;  information on human bird-feeding from the long-term Garden Bird Watch (GBW) program of the British Trust for Ornithology; and observational data on winter presence of blackcaps, also from GBW.   The team analyzed data across a 12-year span starting in 1999. 

Their analysis shows that blackcaps did not become more common in winter-time Britain over these 12 years, but they did show an increasing tendency to winter in Britain's south and west regions, regardless of the winter temperatures each year.  Moreover, blackcaps were more prevalent where food was more frequently available, and especially in suburban areas (where there are likely to be more feeders per hectare than in rural areas.  There is also a possible "heat island" effect, making the gentler climate even more welcoming. Another trend is that the association between blackcaps and artificial food availability got stronger over time. The authors comment, "These novel findings indicate that blackcaps are adapting their feeding habits to exploit human-provisioned foods, and thereby support the hypothesis that the blackcap’s new migratory strategy is likely to have evolved in response to increased human supplementary feeding activities in Britain."

The increased reliance on the seeds and fats supplied by human bird-feeders may not only related to the evolution of migratory habits in this population of blackcaps.  The authors suggest that the growing contribution of such foods to the diet of these birds is reflected as well in changes in the beaks of these east-west migrants:  "Rolshausen et al. (2009) demonstrated that blackcaps wintering in Britain have relatively narrower and longer beaks than those wintering in Spain, suggesting that British migrants have adapted to a more generalist diet. Our results provide empirical evidence that selection for a beak morphology facilitating the handling of seeds and fats supplied in bird feeders has enabled blackcaps to make greater use of supplementary foods provided in British gardens over time."

 Ecological time is more leisurely than the human life-span, though quicker than geological time.  Trends at the level of ecosystems, populations, and landscapes are often very complex, and we often do not know enough about the components in any system to make confidence predictions about the future, nor explain past developments.  To study such systems for long enough, and with enough detail to bring understanding, we need long-term data sets, and networks of observers that give us data across several scales of space as well as time. Such data sets are precious, because their uses will change as the times change, and as the data set grows.  This study is a case in point:  Long-term data sets such as the GBW were mostly not created in order to address questions related to climate change.  Such questions are of urgent interest right now;  who knows what other questions may become urgent, which data sets like this one can help answer?


(This Centerpiece draws from Plummer et al. (2015) Is supplementary feeding in gardens a driver of evolutionary change in a migratory bird species? Global Change Biology (2015) 21, 4353–4363, doi: 10.1111/gcb.13070)



Be on the lookout for new visitors: Carolina Chickadees heading north!

Over the past few decades, many species have moved into New England from the south, while others have moved within New England, or changed their population numbers.   Earlier posts on this blog have reported some examples, and our species inventory includes some other stories. Birds are probably the most noticeable.  Many people pay attention to them, and there's lots of ways to share news of species sightings, first appearance in the spring, and so forth.   With increased awareness of climate change impacts, more people are on the watch for range-shifts, and we sometimes can get "early warning" of possible new visitors or residents to our area.  One of these was reported in 2014:  The Carolina chickadee is moving our way.

In New England, the black-capped chickadee is a familiar and beloved sight, almost a member of the family.  It is the state bird of Maine and Massachusetts, and in the winter time it's a cheery and reliable visitor to back-yard bird feeders.  There are several other chickadees in North America.  To the west you'll see the chestnut-backed.  To the south, there's the Carolina.   This little bird looks very similar to the black-cap, but  it's a little lighter in color, and it has a different song — not the 2-note, piping "fee-bee" of the black-caps, but a 4-note, descending "fee-bee-bay-bay".    It is closely enough related to the black cap that the two can interbreed, and at the boundary between their ranges there is a region where hybrids are fairly common. 

Researchers at Cornell and Villanova studied this zone, looking at changes between 2000 and 2012.  Their data indicates that this zone has moved north at a rage of 0.7 miles a year, reaching nearly to Long Island by that time.  A discussion of the paper notes:  "As a final step, the researchers overlaid temperature records on a map of the overlap zone, drawn from eBird sightings of the two chickadee species. They found the zone of overlap occurred only in areas where the average winter low temperature was between 14 and 20 degrees Fahrenheit. They also used eBird records to estimate where the hybrid zone had been a decade earlier and found the same relationship with temperature existed then. The only difference was that those temperatures had shifted to the north by about seven miles since 2000."

Behind the hybrid zone, naturally, come the Carolina chickadees.    In a few more years, if the trend continues, we might see some changes at New England feeders, and in the New England woods.  Will the Carolinas push the black-caps north?  Will they overlap and co-exist?  Will there be a broader and broader hybrid band?  One of many stories we will see unfold over the next few years.

To read reports on this research, see   and

To read the original paper from Current Biology, see

A new series of resources — Species briefs

 On this website, we maintain a list of all New England species for which there is evidence of climate response, as reported in the scientific literature or in other sources (with links to the sources). (Help us keep up to date! Contact us if you see a gap!).   We believe that in teaching about climate change in our region, the stories of individual species can be interesting and even compelling entry points.

To make this list even more useful, we have begun to create a series of "Species Briefs."  These one-to-two page pieces present some basic information about the distribution and ecology of the species, and then about the reported climate response and its implications.

The first three briefs are about the high-bush blueberry, the dwarf elfin butterfly, and the moose.  More will appear in the coming weeks.These briefs are suitable for classroom use, or for other distribution purposes.  Please use them!  Tell us what you use them for! Send us suggestions for improvement!



Mammalian responses to climate change

In our last post,  we reported on a study of how lungless salamanders are responding to climate change. This week, we’re reading a literature review of mammal studies in North America. 

Photo by notafish

Christy McCain and Sarah King examined 1050 papers that took a look at the ways in which human-caused climate change is affecting mammals in North America. They took pains to include only works that could exclude other factors  that might be causing changes, such as habitat destruction

The first thing to note about this study is that the authors sought, and  found no publication bias. Science deniers often claim that there is a bias toward “popular” results, that is, studies that seem tilted to support mainstream opinion.. McCain and King found that  out of all the studies they looked at, 52% - only slightly more than half - of mammalian populations responded to climate change as researchers expected. Of the remaining 48%, 7% had reacted opposite to expectations, and 41% had no detectable response at all.

Because this was such a broad study, covering species of all types with body sizes ranging from 2.5g  (0.09oz) to 338kg (745lbs), its results have significance for species across the continent, and most likely across the world. 

The researchers drew two main conclusions about likelihood of response to climate change.

Photo by Salix

The first is body size. The larger the animal, the more likely it is to change. Detectable changes started at around 100g (3.5oz), and went up from there to the point where the largest animals (polar bear and elk), were 27 times more likely to show responses to climate change.

The second major indicator is activity over the course of a 24 hour period.  Species that are rigidly confined to activity at a certain time of day are far more likely to show significant changes due to the warming climate than species that can change their activity periods in response to changing conditions. Flexibility is key. 

Eighty-two percent  of the studies focused on changes to range, or to population size, leaving only 18% examining local extinction, seasonal behavior change, morphological change, or genetic change, so more research may be needed in the latter categories. 

In the coming weeks, we’ll list the species covered in this review that live in New England, but the breadth of the study means that it forms a pretty reliable picture of what has been happening with mammals in general as the climate has changed. 

Looking outside New England #1: Shrinking salamanders


The Biosphere and Climate project focuses on climate change in New England, and its effects on our organisms. However, a lot of research is being conducted elsewhere on species that make their home here, and we want to report on this research as well as other findings of interest.

Red-backed salamander, Photo by Rklawton

This week, we report on a study of climate effects on  several species of lungless salamanders. These small and inconspicuous creatures of the forest floor have been shown to play an important role in the energy and nutrient budgets of temperate forests such as those that cover much of eastern North America.  The numbers are  impressive: studies have found as many as 1,000 red-backed salamanders (Plethodon cinereus) per acre in northern hardwood forests. 

There’s not much information on changes in their New England populations due to global climate change, but that’s largely due to the fact that not every species in every country has been studied. In the Smokey Mountains, historical data show that over a period of 55 years, the region has become warmer and drier. Researchers showed that these conditions lead to a faster metabolism, and for six species of the genus Plethodon, the researchers found a significant decrease in body size over the time period in question. Because the researchers focused only on members of the genus Plethodon, so they did not look into changes in other lungless salamanders, or into those with lungs.

Whether or not these changes are currently occurring in New England, they give us a pretty good idea what the response would be if similar changes in climate occur here. Other studies from other parts of the country can provide similar insight into what’s happening to species living in our region, and in the coming weeks, we’ll be providing updates on that research.  

(For more on this study, see ScienceDaily and the original paper in Global Change Biology)