Wrapping Up Sparrow Swap

Thank you all for your support over the last four years.

Sparrow Swap is wrapping up its research! For 2020, we are not asking for data or eggs! We are currently getting our results ready for publication and look forward to sharing our results with you in a more detailed manner soon!

Meanwhile, we’ve attached a brief summary of our findings.

Sparrow Swap 2019 In Review 

Could Egg Removal Lead to Increased Egg Production?

In a 2010 study conducted in Paris, researchers studied feral urban pigeons (Columba livia) to see if egg removal could impact egg-laying cycles. In the study, four pigeon houses with 90 nesting sites were monitored weekly for a 4 year time period. Eggs in the pigeon house were swapped and replaced with fake egg replicas and the nests were monitored, just like Sparrow Swap. One house was used as a control. In this house, eggs were counted weekly but not removed. 


In the control house, researchers determined that the pigeons were nesting on an eleven-week cycle. Pigeons perform courtship behaviors and nest build for two weeks, they then incubate eggs for  17-19 days. Chicks are reared in the nest for 6 weeks. After chicks are reared the process then starts over. In the houses where swaps were performed, it was found that pigeons were laying eggs on a four-week cycle. Researchers found that in the houses with swaps, after 18 days of incubation the pigeons would stop incubation, perform courtship behaviors and nest build for two weeks, then lay another clutch.   

With results showing that egg-laying cycles were shortened, researchers then looked to see if the increased egg production was having an adverse effect on female bird health. Swapped eggs were analyzed to determine the proportion of the egg yolk relative to the egg size. An egg with a high proportion of yolk indicates that the condition of the female is good and has laid a high-quality egg. Low yolk proportion can mean the bird is not strong or healthy enough to produce eggs with enough nutrition to support embryonic development.  The researchers found that in houses where swaps had been performed that egg yolk proportion was lower than the yolk proportion in the control house. This means that females who had eggs repeatedly swapped were producing lower quality eggs than those who had not experienced a swap.  


What Does This Mean For Sparrow Swap? 

It is possible that the same thing could be happening in nest boxes where repeated swaps are occurring, that is why the follow-up visits to the nestbox are so important. By making follow-up visits and documenting when new eggs are laid in the nest we can see if similar nesting cycles are happening in House Sparrows. Our preliminary results indicate that removing makes House Sparrow renest even faster than in boxes with swaps. This study along with our preliminary results show that management strategies can have unintended consequences. Long term studies are necessary to help get a holistic picture of what happens when management strategies are implemented.  Our Sparrow Swap citizen science partners are crucial to help us understand the long-term effects of House Sparrow management strategies. We depend on the nestbox monitoring data to track trends in House Sparrow reproduction. 

Want to learn more? The full paper for the pigeon study can be found at https://www.nrcresearchpress.com/doi/full/10.1139/Z10-044#.XJkjFShKjIU.

Have questions or comments? Email us at sparrowswap@ncsu.edu 

This post was written by Emily Callicutt. To learn more about Skyler and the rest of the Sparrow Swap Team, check out our Team Page.


Jacquin, L., Cazelles, B., Prévot-Julliard, A., Leboucher, G., & Gasparini, J. (2010). Reproduction management affects breeding ecology and reproduction costs in feral urban Pigeons (Columba livia). Canadian Journal of Zoology, 88(8), 781-787. doi:10.1139/z10-044

Behind the Scenes at Sparrow Swap

Sparrow Swap couldn’t be possible without the nestbox monitors who are dedicated to collecting House Sparrow eggs and their observations.

But behind the scenes, there is another important group of people who keep Sparrow Swap running: a dedicated group of undergraduate interns.

Over the last three years 17 undergraduates from four different universities have been part of unpacking eggs, cutting eggs open, entering data, proofreading data, measuring eggshell thickness, writing blog posts.

This past weekend, four Sparrow Swap interns, Carol Gause, Kathryn Jewell, Heather Colter, Cole Parlier graduated from NC State! In addition, Destinee Parson, who cut open a lot of stinky eggs last fall graduated from Peace University.

Carol and Kathryn both went above and beyond as interns by receiving funding from the College of Natural Resources to be able to do an independent project within Sparrow Swap.

Carol, did her project looking at what happens to native birds nesting nearby following a removal. She also was hard at work exploring the potential to test the eggs for different contaminants.

Kathryn’s project looked at the differences in thickness across development stages and was recognized for having an outstanding poster!

Heather finished her internship with Sparrow Swap last summer and created a cart to tell visitors at the Museum of Natural Sciences about Sparrow Swap. She also wrote a blog post last summer about her experiences as a Sparrow Swap intern.

To learn more about the Sparrow Swap Team, check out our Team Page. 

Analyzing House Sparrow Eggs for Environmental Contaminants

If you’ve ever looked through our Sparrow Swap website, we mention that we hope for our House Sparrow eggs to be analyzed for contaminants as part of research to determine if House Sparrow eggs are useful indicators of human exposure to environmental contaminants. We are currently looking at heavy metals in the eggshells, but hope to also look at other persistent environmental contaminants in the egg contents

Before we decide on what contaminants to test the eggs for we have to consider the feasibility of testing eggs for contaminants, explore why we should be testing for certain contaminants, and understand what research has already been done. To do so we look at the work of other scientists studying contaminant in bird eggs including Dr. Seth Newsome at the University of Wyoming and Dr. Nellie Tsipoura at the New Jersey Meadowlands Commission.

A male Peregrine Falcon

Flame retardants and Peregrine Falcons
One contaminant of emerging concern among wildlife, including birds, are flame retardants. Flame retardants are primarily composed of polybrominated diphenyl ethers (PBDEs for short). These fire retardants are in many items that can be found in virtually every household. PBDEs are added to carpets, furniture, electronics, and even buildings and cars in order to reduce the flammability of these products. PBDEs have recently become a contaminant of interest due to its ubiquitous nature, but not much is known of the effects of PBDEs on organisms and the environment. In 2010, Newsome et al. published a study in Environmental Science & Technology that investigated the presence of flame retardants in peregrine falcon eggs. These researchers found that high levels of PBDEs were present in the eggs of peregrine falcons that were collected from California cities. They concluded that the PBDE concentrations in urban peregrine falcon eggs were significantly higher than the eggs from rural areas. As a result, this study was able to identify a connection between diets composed of food produced by humans and high PBDE concentrations. The Sparrow Swap Team is also planning to use the membrane of the eggshell to determine the diet of the female. This may tell us if House Sparrow diets are similar to humans which could mean that we may be exposed to similar contaminants found in the House Sparrow eggs.

This study is very reminiscent of a previous study that was popularized by Rachel Carson in her book Silent Spring. Alarming levels of dichlorodiphenyltrichloroethane (DDT) were found present in peregrine falcon eggs. Eventually, scientists were able to connect the widespread use of DDT to the large population declines in peregrine falcons, as well as other raptor populations. Eggshell thinning, which caused reproductive success to greatly decline, was occurring due to DDT accumulating in these organisms via dietary pathways. Eerily similar circumstances are occurring right now with peregrine falcons, along with other wildlife. We are also measuring eggshell thickness, particularly how thickness may be associated with heavy metal concentrations.

Waterfowl at the New Jersey Meadowlands

Heavy Metals and Canada Geese
Heavy metals, such as lead, mercury, cadmium, and more, are also of concern. We are testing the House Sparrow eggs that our Citizen Scientists have collected for lead, cadmium, arsenic, copper, and selenium. These contaminants are of concern due to their ability to accumulate in sediments and in organisms. These heavy metals are particularly known for their ability to bioaccumulate in organisms, which occurs when the intake rate of a substance is greater than the excretion rate by the organism. As a result, contaminant concentrations within an organism tend to be higher than the concentrations in the environment around it.
In a previous study conducted by Dr. Nellie Tsipoura at the NJ Meadowlands Commission, Canada Geese living within the New Jersey Meadowlands in 2010, known for its heavy pollution from effluent and runoff from nearby industries and traffic, were tested for Lead, Cadmium, Arsenic, Copper, and Selenium. In this study, researchers collected the eggs, along with feathers, muscle, and liver tissue of the Canada Geese. The eggs collected from the Meadowlands were found to have higher lead levels when compared to Canada geese eggs collected from other areas as well as eggs from other bird species living within the same habitat. These higher lead concentrations are concerning because it is possible that the concentrations will be passed on to predators after they consume the eggs. The researchers noted that this opens the possibility for many levels of the food chain to be contaminated, even humans. The presence of the contaminants represents a possible threat to humans, as well as other wildlife in the area that may be exposed to these heavy metals, either through direct exposure or through dietary pathways.

Our Next Steps
Similar to these studies, we are analyzing the House Sparrow eggs that we have received for environmental contaminants. We are taking the first steps to see if House Sparrow eggs can be used as an indicator for contamination in wildlife and potentially in humans.

Want to learn more, here are the original articles:
PBDE Study: https://pubs.acs.org/doi/10.1021/es100658e
Heavy Metal Study: https://www-sciencedirect-com.prox.lib.ncsu.edu/science/article/pii/S0013935111001423

This post was written by Skyler Price. To learn more about Skyler and the rest of the Sparrow Swap Team, check out our Team Page.

A new season is upon us!

We hope ya’ll are getting excited about the 2019 breeding season!

Curious about 2018? Check out our summary of 2018! 

This year we have a couple of exciting changes.

  1. We are back to two options Swap or Remove. You’ll notice though that the swap and remover datasheets are a little longer! This year we are asking everyone to include information about native species in neighboring nestboxes.
  2. We are no longer asking for folks to mail in House Sparrow eggs. We are still busy measuring thickness and analyzing the data we’ve gotten. We are taking a break from receiving eggs this year so we can get some findings back to you.

To hopefully make the instructions easier, we’ve created a slide show video of the instructions!

100 Years of the Migratory Bird Act

This year marks 100 years since the passage of the Migratory Birds Treaty Act, one of the earliest pieces of conservation legislation passed by the US Government. This law made it illegal to kill native birds or remove or disturb their nest and eggs. (16 US Code Section 704 subsection A) This act served to protect many endangered species of birds which were under threat from over hunting like waterfowl whose feathers were highly prized. This act has seen many successes and has helped replenish and protect many bird species like the Snowy Egret and other waterfowl.

On side effect of this law was that egg collecting became an illegal hobby. While this act was extremely good protecting birds, it also means most of the eggs we have in Museum collections are now a 100 years old. Bird eggs can be valuable sources of data regarding pollution and environmental damages, and this data can be invaluable in crafting governmental responses to these threats. In a very real sense birds are, for the lack of a better phrase, a canary in the coal mine. For example the impact that DDT and similar pesticides were having on bird eggs were noticed far earlier than its impacts were seen or felt on humans, as illustrated in the work of Rachel Carson in Silent Spring. As such bird eggs can serve as a vital tool for scientists when considering the impact of contaminants in the ecosystem and their potential impacts on human life.

The Migratory Bird Treaties Act has presented a challenge and an opportunity for scientists interested in studying birds for contaminants. The challenge is that because much of the avian life in the United States is composed of native bird species, which are protected under the Migratory Bird Treaties Act, scientists cannot easily collect bird eggs from these birds. However, nnon-native birds, such as the House Sparrows, are exempt from the law. House Sparrows are native to western Eurasia and Northern Africa. these birds were introduced to NY in the 1800’s and have since spread across the US. There non-native status allows Sparrow Swap to revive the egg collecting so that House Sparrow eggs can be used to research pollutants, and more importantly in terms of helping conserve native species, swapping out the eggs allows us to study a method for controlling this invasive species.

However, because only house sparrow eggs and a handful of other species are legal to collect makes it very important that the eggs collected are indeed House Sparrow eggs. The color, speckling, and shape of an egg can change a lot not only between species, but also within a single species. This can make it hard sometimes to confirm just by looking at an egg, what species it is from. Where the nest is (in a cavity or in a tree), what the nest is made of (pine needles or moss), the structure of the nest (neat or messy) and if you see an adult bird fly in and out of the nest are all important clues that can confirm the identity of the eggs. For example, House Sparrow nests are made of coarse dried vegetation, often stuffed into the hole until it’s nearly filled. The birds then use finer material, including feathers, string, and paper, for the lining.

Below are a few examples of other species with similar eggs to house sparrows:

House Sparrow Eggs. Photo from Sialis.org


Cowbirds are indigenous birds which will sometimes parasitize a sparrows nest by laying an egg in the nest. As such they are protected by the Migratory Bird Treaties act and their eggs cannot be removed from a nest without permission from your States wildlife management agency. Please remember that while the two eggs look similar, that one is a house sparrows egg, and one is a cowbirds. An easy way to tell the difference is to look at the size (if they are in the same nest) and the degree to which the eggs are round. The larger and more round one of these eggs are the more likely they are cowbird eggs. In addition if there are other intact eggs of another bird species in the nest or adult birds brooding, it is likely that the eggs are cowbird eggs unless the brooding birds are House Sparrows.

Cowbird egg in a bluebird nest. Photo from Nestwatch.

Tufted Titmouse
Tufted titmouse eggs and those are also protected species and you can tell the difference between the two since House Sparrow eggs are generally glossier and a bit longer on average than a Tufted Titmouse egg. Titmice build cup-shaped nests inside the nest cavity using damp leaves, moss and grasses, and bark strips. They line this cup with soft materials such as hair, fur, wool, and cotton, sometimes plucking hairs directly from living mammals.

Tufted Titmouse Eggs. From Sialis.org

House Finch
We have also received House Finch eggs, these birds are also protected species. Compared to a House Sparrow the Eggs of a House Finch are smaller, lighter colored, generally less speckled, and the speckles are generally black to purple in color. A House Finch’s nest is a cup made of fine stems, leaves, rootlets, thin twigs, string, wool, and feathers, with similar, but finer materials for the lining. This what House Finch Eggs look like.

House Finch Eggs. Photo from Nestwatch.

We hope this helps if you come across an unusual egg! Don’t hesitate to contact us hear at Sparrow Swap if you have any questions.

This post was written by Rohan Krishnamoorthy. To learn more about Rohan and the rest of the Sparrow Swap Team, check out our Team Page.

Double Yolker!

In order to test the eggs for contaminants, we first have to separate the egg contents from the eggshell. To do this we use a dremel tool to carefully cut through the eggshell, but not the membrane. We then lift up the piece of cut eggshell. Here, there is always a moment of hesitation: what will be inside?

Sometimes we find a nice yellow yolk with a viscus albumen (the whites). However, as the eggs age, both the yolk and albumen start to break down making them runny. On other instances we find more developed embryos, and to be honest, the scene can be quite gruesome.

The worst, by far, is a rotten egg. Sometimes just with the slightest touch of the dremel, the egg will explode sending shell and contents everywhere. For example, one of our middle school interns picked a piece of shell out of my hair.

But occasionally, we will find something surprising. Like a double yolker! While taking photos of the clutch, Aubrey noticed that one egg was bigger than the others in the clutch (Egg C).

When we went to curate it, we found not one, but two perfect yolks.
I’m not sure anyone has ever looked at the odds for house sparrows, but for chickens the odds of getting a double yolker is about 1 in 1,000. Just as in humans, twin birds can be fraternal or paternal. If a female produces two yolks in a short enough time span (about three hours), than both yolks will travel through the oviduct together as one egg creating fraternal twins. If the embryo splits within the egg during development than the twins will be paternal. Most of these twins will die in the egg completing for the same resources. However, there are some cases where twin egg are able to successfully hatch!

One of these cases happens to be in bluebirds! Back in 2013, a Nestwatch volunteer in State College Pennsylvania found more nestlings in a nest of bluebird than there had been eggs! Twins had successfully hatched! These rare occurrences can only be documented through having vigilant and dedicated nestbox monitors and naturalists around the world.

This post was written by Suzanne Hartley, to learn more about Suzanne and the rest of the team check out the Sparrow Swap Team page.

A day in the life of a Sparrow Swap intern.

Hi all! My name is Heather Colter and I intern at the biodiversity lab in North Carolina Museum of Natural Sciences for Sparrow Swap! A little background info, I am going to be a senior in the fall at NC State University and my major is Fisheries, Wildlife, and Conservation Biology in the College of Natural Resources. I have really enjoyed my time with the Sparrow Swap team learning not only the technicalities of the project, but also getting to know the members and leaders within. Not to toot any horns, but the interns who work with Sparrow Swap are really important to the whole of the project; we work really hard to keep everything straight.

One of my favorite aspects of the project is when we go out into Raleigh and check the various boxes we have put out. It’s always such a treat when we find eggs, or, like in the photo above, when those eggs have hatched and become fresh baby birds! This photo was taken at the Farmer’s Market in Raleigh, it is a clutch of house wren chicks; the parents were nearby making a ruckus but it was a great find nonetheless! It was extra special because the six eggs we had counted in the previous week turned into six healthy and alive chicks, so that’s a great bonus.

Other duties for the interns include neverending data-entry/proofing, measurements of eggshell thickness, and curation of the clutches sent to us. Curation happens before we can get to measuring thickness; for curation we take the eggs and we measure their length and width and take a final mass to determine if there was any leakage or “weeping” since the egg first came to us and we took its initial weight. After that we use a Dremel tool to cut through the shell and then we poke through the membrane underneath with a instrument resembling a long metal toothpick. We then jar the contents of the egg if able to, and then we wash out the inside of the eggshell and leave it to dry and then we mark it with the clutch number and specific letter (A, B, C, D…) with an archival pen and store them until someone is ready to take their thickness measurements. Measuring the thickness is done with a tool called a micrometer, and we take six individual measurements of the sawed off cap of each egg within each clutch, or we use a broken piece of the eggshell if there isn’t a cap to measure. Of course, we write down all of these measurements into sheets, along with notes, and then we enter the information into the Sparrow Swap database. Working with Sparrow Swap has been an amazing opportunity and I have enjoyed it every step of the way!

This post was written by Heather Colter. To learn more about Heather and the rest of the Sparrow Swap Team, check out our Team Page.

A pest around the world

How did house sparrows become a pest? With the spread of agriculture and urbanization sparrows have become one of the abundant groups of birds in the world. Most sparrow species are closely linked with humans and spread with people as humans moved out of Africa and throughout the world. Perhaps the most successful sparrow, and the one we all know about, is the house sparrow, who can be found on every continent in the world save frigid Antarctica. Throughout time, as their abundance has fluctuated so has public opinion about these resilient little birds. Today we will look at the story of sparrows around the world, and how public perceptions and management has changed over time.


As humans moved out of Africa and into Europe, so did our sparrow friends. Being mostly seed eaters, sparrow ancestors were migratory. But the development of agriculture gave sparrows a consistent source of food year round. Like us, they settled, nesting in the buildings we built and eating the crops we produced. During the 1700’s there was an explosion in the European sparrow population as human settlements spread further and agriculture continued to focus on cereal grains such as wheat and oats, an ideal food source for sparrows.

By the mid 1700’s there was a superabundance of sparrows throughout Central Europe, with some written accounts describing flocks of sparrows so large that they blocked out the sun. These enormous flocks of sparrows could decimate important crop yields at a time when cereal grains made up a substantial portion of crops grown in Europe, making the sparrow a worthy foe. To combat this problem, many local governments established a bounty in which sparrow heads could be turned in to the government for tax credits. By the end of World War II, the first observable declines in the European sparrow population were seen. This change is likely due to a decrease in horse manure, more efficient grain harvesting technology, and poultry no longer being fed in the open. It is difficult to know whether the management strategies implemented by governments have led to a continued decline in house sparrow numbers or whether changes agricultural practices have played a bigger role. Ironically, in many European countries today house sparrows are now a protected species as their numbers have declined so much. There are now campaigns in the United Kingdom to save the house sparrow!

A house sparrow eating grain from a bird feeder. Photograph by Tammy McLean


One of the most interesting stories of sparrow control comes from China, during the reign of Mao Zedong and “The Great Leap Forward”. Mao considered the Eurasian tree sparrow (a close relative of the house sparrow) one of the “four great pests” to the nation because of their abundance and negative impact on grain crop yields. In March of 1958 Mao declared war on tree sparrows, and people all over the country went outside banging pots and pans together, waving flags, destroying nests, and killing nestlings with guns and slingshots.

At first, the effort appeared to be a remarkable success as crop yields initially improved. But before long, locust and grasshopper populations, freed from sparrow predation, exploded and decimated the grain crops. The crop damage from the insects lead to a famine in which more than 35 million Chinese people died. In a desperate attempt to stop the destruction, the government began importing sparrows from the Soviet Union. Following this disaster, Mao quickly protected tree sparrows and added bedbugs to his lest of four pests instead. This example illustrates the severe damage that can be inflicted when sweeping changes are made to an ecosystem.

Shen Nan (沈枬)
1959, February
Eliminating the last sparrow
This poster was meant for use in schools, and was part of a series. Sparrows were one of the Four Pests, together with flies, mosquitoes, and rats.


What can we learn from these failures in providing effective management of pest species? In both the European and Chinese stories, the problem came from a basic misunderstanding of how sparrows function in an ecosystem. Prior to the European sparrow population explosion of the 1700’s, written accounts show that some were already advocating for control of sparrows by destroying nests and eggs. But it wasn’t until the population exploded and started decimating crops that any action was taken. In China’s case, the government thought that tree sparrows strictly fed on seeds, and it wasn’t until after the sparrow population had been destroyed that they found research showing that tree sparrows also can control insect populations because they do feed on insects during breeding season.

The sparrows in China and Europe were a native species, but house sparrows were purposely introduced from Great Britain to the United States in the 1850’s as a form of pest control. 50 years after their introduction, house sparrows had spread virtually across the entire country and are almost universally regarded as pests. Instead of providing pest control, house sparrows are competing with our native bluebirds, and this all stemmed from a lack of understanding of the species.
These stories highlight the importance of incorporating good science into management strategies for wildlife. With your help on the Sparrow Swap Project, we will be able to improve our understanding of how different management strategies impact house sparrows and native birds, which will hopefully ultimately lead to better management decisions in the future. By participating, you are providing data and increasing knowledge that will be instrumental in providing effective management for our native songbirds.


If you would like to learn more about the “4 pests campaign in China, check out this article!
If you are interested in reading more about the story of sparrows in general, check out tthis article written by NC State Professor Rob Dunn!

This post was written by Dominic Eannarino, a recent graduate from NC State. You can learn more about Dominic and the rest of the Sparrow Swap Team on our team page.

Sparrow Swap Q & A

On June 13th,2018 we held our first live Q & A about Sparrow Swap! Hopefully there will be more in the future!
You can watch the video here!