Changing weather patterns are playing havoc with nature’s ecosystems. We’re seeing such things as plants flowering in winter, prompting butterflies to emerge earlier and birds to lay eggs sooner so their chicks can fatten up on the new bounty.
But why are some bird species advancing the timing of their seasonal patterns while others are delaying, and some don’t seem to be reacting at all?
That’s a question Finnish and US researchers set out to explore by looking at changes in breeding seasons across Finland’s boreal regions.
They found many bird species appear to have shortened their breeding season, and those that breed earlier seem to adapt better to warming climates, reporting their findings in the journal Proceedings of the National Academy of Sciences.
Identifying these changes is important, because even seemingly small adjustments can trigger complex reactions that quickly ripple throughout ecosystems.
When it comes to birds, they need to time their breeding so it’s in sync with peak food abundance to keep their species reproducing successfully.
Longer breeding periods might reflect extended conditions that favour breeding, while shorter seasons could indicate smaller windows of opportunity for tapping resources. How birds adapt to these is critical for survival.
To gain a broad perspective on their responses to changing seasons, Maria Hällfors, from the University of Helsinki, and colleagues accessed four decades of data curated at the Finnish Museum of Natural History comprising more than 820,000 nesting records of 73 bird species.
They investigated hatching time for bird chicks using the timing of ringing (nestlings can only be ringed at a certain size, and this corresponds to egg-laying dates) to determine the beginning, end and length of different species’ breeding periods.
Using a joint species distribution modelling framework, the team discovered that, on average, bird species both advanced and shortened their breeding season, starting 4.6 days earlier and breeding for 1.7 days less than 43 years ago, during which time the average temperature in Finland rose by 0.8 to 1.6 degrees Celsius.
Overall, a third shortened their breeding period in at least one bioclimatic zone. Notably, this was more common in short-distance migrators and those that stay at home – species that typically breed earlier and have shorter seasons than long-distance migrators.
This suggests those species can respond more quickly to environmental cues and better adapt to warmer conditions, the authors say, offering insights into different responses to seasonal changes and broader ecosystem impacts.
“Most importantly,” they write, “our study suggests that evaluating changes throughout the season is crucial, as earlier and shorter breeding periods in birds may alter community-wide patterns of species co-occurrence and tropic relations across the boreal region.”