A new paper co-written by Memorial University researchers argues that some migratory birds are failing to keep pace with a rapidly changing climate.
Dr. Stephen Mayor completed a master’s in biology at Memorial and is currently with the Florida Museum of Natural History in Gainesville.
As a post-doctoral fellow at Memorial, he worked with Dr. David Schneider, Department of Ocean Sciences, on a study that looked at 48 common bird species and their ability to adjust the timing of their migration to match the changing start of spring.
“What we’re seeing is that climate change is causing the timing of spring green-up — that’s when the leaves come out on the trees — to shift,” he explained.
“It’s also become less variable and less predictable from year-to-year. We looked at how birds were responding to that shift and found nine species of songbirds are having trouble keeping up with the change and lagging behind when they should be arriving to North America.”
While most species could adjust their arrival dates, the birds that were unable to shift their departure time and transit speeds included great crested flycatchers, indigo buntings, scarlet tanagers, rose-breasted grosbeaks, eastern wood pewees, yellow-billed cuckoos, northern parulas, blue-winged warblers and Townsend’s warblers.
In Eastern North America, where the researchers found spring is coming earlier, the arrival of eastern breeding birds is increasingly lagging, whereas in the west, where green-up is unexpectedly starting later, the birds arrived increasingly earlier relative to the timing of spring.
“The later spring in Western North America was a big surprise,” said Dr. Mayor.
“We didn’t expect that at all. The birds are trying to keep up, but they aren’t doing a very good job of tracking those changes and they are falling behind. What you could end up with is this eerie situation where it feels like spring outside but there are no birds singing.”
For migratory birds, a properly timed arrival at their breeding grounds is a critical event that sets the stage for the remainder of the season, impacting offspring survival and performance.
Breeding, egg laying and fledging must coincide with optimal habitat conditions and food availability, which means birds must correctly anticipate what spring breeding site conditions will be while they are still at their winter grounds, often thousands of kilometres away.
“Arriving too early can bring risk of freezing, and missing peak resource abundance, whereas arriving too late can mean fewer available nest sites, and declining resource abundance,” said Dr. Mayor.
It can all lead to fewer chicks with a reduced rate of survival and ultimately population declines and biodiversity loss. That could set off a cascade affect, whereby fewer predators can cause insect outbreaks and a subsequent increase in the defoliation of trees.
The researchers arrived at their conclusions by studying satellite images from NASA, which revealed the timing of spring green-up across North America.
“People should know their efforts are actually being used in science.”
They compared that to citizen science data posted at eBird.org by birders recording their observations — where and when they saw a bird — and used it to figure out when birds arrived at a given location.
“It’s important to emphasize the citizen science contribution because people should know their efforts are actually being used in science,” said Dr. Mayor.
“Hopefully it will also get other people interested in reporting.”
Dr. Mayor believes it’s essential to have more reports from Newfoundland and Labrador and other rural Canadian locations, so that the trends in birds aren’t driven so strongly by observations in and around populated areas.
“If you have thousands of people reporting the same birds in New York City, it doesn’t really provide you with much information, but if you have people reporting from an outport on the South Coast of Newfoundland, that data is much more valuable to us,” said Dr. Mayor.
Previous bird studies have predicted that climate change will drive hundreds of bird species to extinction and greatly reduce the range of others.
“If you have people reporting from an outport on the South Coast of Newfoundland, that data is much more valuable to us.”
Dr. Mayor and his fellow researchers are now hoping to figure out why most of the 48 bird species were able to adjust to climate change, while others were not, and what those demographic impacts may be.
“We would like to know what causes some species to fail at tracking this change in spring, whereas others seem to be doing perfectly okay,” he said.
“We’d also like to get a better grasp on whether this increasing mismatch is impacting populations to see if those birds are declining. If it is affecting these common species, we really worry about what also might be happening with the rarer species.”
The research was funded by the Natural Sciences and Engineering Research Council of Canada.