“They’re understudied and under-appreciated.”
Buzzing, biting or just plain annoying, insects are summer pests to us. But insects are the main course for Minnesota’s flying insectivores. Amber Ulseth, a NRRI aquatic ecologist who helped sift through a year of terrestrial insect data, said there’s just so much more to learn.
“This study has the potential to help us understand just how important these insects are in these landscapes,” Ulseth added.
And for tree swallows – the focus bird species for this research – insects are the entree, the main course and the dessert. Tree swallows were chosen for this study because they’re one of many aerial insectivore species in decline. They’re also nest box dwellers, allowing researchers to place boxes attracting birds to the study areas to track bird activity. Equally important, tree swallows are food “generalists,” meaning they eat what’s available.
NRRI’s Avian Ecology Lab scientists teamed up with NRRI entomologists (scientists who study insects) to launch this unique study to find out if the swallows have enough food sources in western Minnesota to thrive.
The researchers monitored 95 nest boxes set up across three study areas: farmland, prairie grasslands and areas with a 50/50 mix of both. The nest boxes were outfitted with microcomputers to collect information from tagged birds flying in and out of the box to measure how often the parents were feeding the young birds. They also collected nestling feces to analyze with eDNA technology to know exactly what the nestlings were eating. Overall, they collected data on 74 adult tree swallows and 508 nestlings.
“We found that for the tree swallows, at least, there are plenty of insects to support reproduction and productivity,” said Alexis Grinde, NRRI Avian Ecology team leader. “But we also know there are a lot of birds that specialize in what they can eat and forage for. So this study is an important first step to learn more about aerial insectivores.”
Results
The two-year study provided some preliminary data that will be used to design a more comprehensive study.
- Breeding was more successful in areas with a higher proportion of grasslands and dense vegetation.
- Nestlings grew fastest in grassland and mixed habitats, suggesting that they had access to higher-quality prey (insects) in those areas.
- Tree Swallows have a diverse diet. Researchers identified 482 different insect genera in the tree swallow diet, including flies, beetles and moths.
- Insect data showed the same abundance patterns as the tree swallow diets, confirming that these birds are generalists and feeding their nestlings the most abundant available food.
- Of the 57 breeding bird species identified in the study areas (13 of which are “Species of Greatest Conservation Need”), grasslands supported the most diverse bird communities, and all species that are of conservation concern were found in grassland habitats.
An important take-away from the study is that grassland habitats are really important to bird biodiversity.
“Conservation practices in agricultural lands that promote habitat features and support insect abundance, such as buffer strips, seem to increase food availability for breeding birds,” said Grinde. “Conserving and creating grassland habitat is important and there are opportunities to increase the quality of agricultural lands too; we’re here to help inform those decisions.”
Insect Challenge
There are many challenges to studying terrestrial insects, not the least of which is the sheer number. Minnesota is home to some 700 insect families with an estimated 8,000 to 10,000 species in each family.
And this isn’t lost on picnicking families.
“Insects are not exactly our ‘charismatic megafauna’,” said Ulseth. “It’s harder to sell people and research funders on the important ecosystem services provided by these creatures. Teaming-up with the avian ecology lab was a great opportunity to get baseline data and think about food webs.”
The insect data collected by aerial traps and net sweeps reflected the findings in the eDNA of tree swallow feces. But other bird species need to be studied, like the bobolink, eastern meadowlark and sedge wren.
“Can the other sensitive bird species breed successfully in these habitats? Are there enough insects available during the peak of the breeding season for all birds? How do the extreme weather events and droughts we have been experiencing influence the insects that are available year-to-year?” asked Grinde.
That’s the future direction, to focus on the diets of other species and continue looking at changes in timing of food availability related to weather and climate.”
This preliminary study was funded by the Environment and Natural Resources Trust fund as recommended by the Legislative Citizen Commission on Minnesota Resources (LCCMR) .
Read about the first year of this study here: What’s buggin’ Minnesota birds? September 2023
PHOTO TOP: A tree swallow holds tight to its damselfly meal while being held by Annie Bracey for the study.