A new study led by the University of Oulu explored how changes in moth abundance affect insect-eating birds in Finland. The findings reveal that the impact of moths as a food source varies between bird groups and is generally stronger in northern areas.

The study found a positive association between the
abundance of moths (Lepidoptera) overwintering as eggs or adults and the abundance
of resident or long-distance migrating forest birds, which are reliant on
caterpillars as food source during their breeding season in the spring. The results
indicate that early-season moth abundance significantly influences bird abundance,
and particularly in the north-boreal zone. This highlights how species interactions
depend on their environment and suggests that declines in insect populations could
lead to declines in their bird predators.

However, a similar
dependency of bird abundance on moth abundance was not found in southern and central
parts of Finland, or for moths that are available for the birds later in the
season.

“The reason why moth abundance affected bird abundance
only in northern Finland is that in the north bird breeding seasons are short, food
webs are relatively simple, and temporal moth abundance fluctuations from year to
year are naturally strong. Therefore, abundance changes of a particular group of
insect prey more likely reflect in bird abundance in northern Finland than in
central or southern Finland”, explains Mahtab
Yazdanian, the lead author and doctoral researcher at the University
of Oulu. 

“In other words, birds in the north are more
reliant on moth preys compared to birds in the central and southern regions of
Finland.”

The research team was led by the University of Oulu and
included experts from Finnish Environment Institute (SYKE), Finnish Museum of
Natural History (LUOMUS), Vrije Universiteit Brussel and from the Arctic Centre at
the University of Lapland, University Researcher Jukka
Jokimäki. 

Long-term
monitoring data is valuable

The study drew on 26
years of monitoring data.

“This study highlights the value of
long-term monitoring programmes. We are fortunate in Finland to have detailed
abundance data for both moths and birds, which our study combines in full for the
first time.”, explains Tuomas Kankaanpää, a postdoctoral researcher at the
University of Oulu.
Such comprehensive temporal and spatial datasets are
rare worldwide. Deeper insights into ecological dynamics are gained, and the
complexities of natural systems are better understood through the investigation of
these datasets. 

The new study demonstrates that using
long-term data in combination with information on birds’ migratory strategies and
seasonal availability of different moth species facilitates uncovering regional
differences in interactions between moths and their bird
predators. 

The research article Evidence for bottom-up effects of moth abundance on
forest birds in the north-boreal zone alone was published in the highly
esteemed Ecology Letters journal in December 2024.

More information:

Mahtab
Yazdanian, Doctoral Researcher, 0449521669, Mahtab.yazdanian@oulu.fi, Ecology and
Genetics Research Unit, University of Oulu

Tuomas
Kankaanpää, Postdoctoral Researcher, 0503085184, Tuomas.kankaanpaa@oulu.fi, Ecology
and Genetics Research Unit, University of Oulu

News article at the website of the University of
Oulu