Has much scientific research been conducted on Tree Swallows?
Ready for a surprise? The species of choice for many North American ornithologists
pursuing songbird research is - - - the Tree Swallow!
Very few people outside the professional ornithological community are aware of the
important contributions of Tree Swallows to scientific research. Over 500
professional journal articles that focused on or used Tree Swallows as experimental
subjects have been published since 1980. This is far more than for bluebirds, robins,
cardinals, chickadees, and other favorites - combined. (Please note: we are referring
to scientific articles, not anecdotes in birding or hobbyist magazines, which though
interesting are not subjected to rigorous scientific standards). Some ornithologists
have gone so far as to state the Tree Swallow should be acknowledged a "model
species" for the significance of its role in biological, ecological and behavioral
research on birds. For many ornithologist they are the songbird equivalent of fruit
flies, nematode worms, zebra fish, and lab mice. Not a very glamorous group you
say? Maybe not, but important in research? Very!
What makes Tree Swallows such valuable research subjects?
Ornithologists have found, as you are finding, that Tree Swallows offer great
opportunities for learning because:
- Tree Swallows breed over much of North America, are easily attracted to nest
boxes, and will nest relatively near one another.
- Research grids with hundreds of nesting pairs can be established, giving
scientists the large sample sizes needed for statistically valid conclusions.
- Box-nesting allows many conditions to be standardized or manipulated
experimentally, and box-nesting Tree Swallows are much easier to trap than
- These swallows have good return rates and ease of recapture which allows
experimental variables to be tracked and measured over several years time.
- Swallows can be uniquely color-marked for ease of recognition in the field.
- This species can be captured, handled, and tested with low risk of desertion.
- Much of Tree Swallow behavior occurs out in the open where it can be easily
observed and measured.
What has been learned from Tree Swallow research?
The list is long and impressive. For instance:
- Much pioneering work on reproductive behavior and mating systems of birds
used Tree Swallows as subjects. A great deal of what is known about nest site
competition, extrapair paternity, mate guarding vs. frequent copulation,
control of copulation, role of floaters, parental investment, seasonal
reproductive effects, nestling growth and development, and infanticide was
discovered or confirmed by scientists working with Tree Swallows.
- Tree Swallows are the focus of a 30+ year investigation of interrelationships
among, food supply, weather factors, and reproductive success.
- The complexities of begging behavior of songbird nestlings and responses of
parents are being studied using cameras and recording equipment within
- The very extensive banding records for this species have allowed study of
breeding dispersal of adults and juveniles over large geographical areas.
- Doppler radar and mini geolocators are being employed to investigate Tree
Swallow migration routes and location and usage rates of stopover sites.
- Thousands of Tree Swallow nest records from over 40 years have documented a
significant advance in laying date in some parts of North America, which has
been cited by some persons as evidence for global warming.
- Clutch size and brood size have been manipulated in many ways to investigate
various aspects of reproductive performance.
- Adult Tree Swallows have been temporarily handicapped to examine their
ability to forage for their young.
- Box nesting in Tree Swallows has made it convenient for exploring effects of
ectoparasite loads on nestling growth and survival.
- Tree Swallows have had their diets supplemented, and have been bled,
inoculated, and irradiated in various experiments investigating their
biochemical and physiological responses.
- Recently it's become a common procedure for government agencies and private
corporations to utilize Tree Swallows in monitoring ecotoxicology. Box grids
are established near suspected sources of hazardous water-borne
environmental contaminants. Tissues collected from swallow eggs, nestlings
and adults are then analysed to monitor extent and effect of contaminant
spread from aquatic to terrestrial ecosystems.
- Tree Swallows are being used in the study of senescence on reproductive
success and immune system function, and their chromosomes' telomeres have
been studied for their role in aging and lifespan in birds.
- An ambitious and truly unique project, Golondrinas de las Americas, has been
launched whose purpose is to compare the biology, ecology, behavior,and
genetics of all nine members of genus Tachycineta. Dozens of Golondrinas
study sites have been established throughout the New World (see map below
from their web site - Tree Swallow locations in blue), and data has begun to be
reported in the scientific journals. Check out the Golondrinas web site to get
a sense of the scope of this project.
If you didn't realize all this research was and is being undertaken you're not alone.
Certainly the average birder has no clue that in the exploration of songbird biology,
ecology and behavior the contribution of Tree Swallows has been huge.
If you would like to examine particular topics in depth you can refer to the journal
articles in our Tree Swallow Research Bibliography. Nearly all the studies listed there
used Tree Swallows as either the primary research subject or as a comparison
species. These articles aren't exactly "light reading" and you're not going to find
them in your public library. You may be able to find some of the more recent ones
online, but for most you'll need to visit college libraries.
Learn About Birds at Tree Swallow Nest Box Projects
Sampling a nestling's blood. Photo courtesy of Golondrinas de las Americas.
A DNA Gel with showing microsatellite loci used to determine parentage
of a Tree Swallow brood. Photo courtesy of Dr. Linda Whittingham.