How are bird migrations visualized?
A comprehensive review of the history, measurement methods, and visualization patterns of our migratory flying friends
Long post alert! But this was about birds so felt totally worth it. 🐦 🐤📊 📉
Bird migration is the annual, large scale movement of birds from locations of lower food and nesting resources to locations with higher resources. Bird migration is important to study because it gives us insights on bird movements, their behavior, and relevant concepts such as bird evolution, climate change, habitat, and species conservation. Bird migration charts are tools to visualize these complex bird movements across the globe which are relevant for scientific as well as general public consumption. Collecting data to create these visualizations is difficult and is done by using different methods like bird ringing, counting, radio and satellite tracking, geo-logging, radar tracking. The data collection method used has an impact on how the bird migration chart is visualized. This report summarizes current state-of-the-art tools used for the data collection on bird migration and the visualization tools that support the discovery and advancement of the field.
Bird migration is the annual large scale movement of birds between their summer breeding grounds and winter non-breeding grounds across the globe . This migration is largely from a location low in resources such as food and nesting sites to a location rich in these resources. Bird migration can be classified in four types depending on the distance the birds cover — permanent residents, short distance, medium distance and long-distance migrants. Permanent residents don’t migrate at all. Short distance migrants fly short distances, for instance, from higher to lower elevation on a mountainside. Medium distance migrants can distances that scale several states. Long-distance migrants can cover distances as large as across continents. For instance, birds migrate from United States and Canada to wintering grounds in Central and South America.
This research topic is important because of the following reasons. First, tracking birds is challenging. They are on-air as against land. Second, they cover long distances, rarely covered by other species. Third, studying bird migration can help us study the evolution of birds as compared to other species, and how they have survived all these eras. Forth, it is helpful in studying changing seasonal patterns and climate change. Fifth, it can help in taking decisions for the conservation of natural habitats and bird species. Sixth, visualizations are a means to study bird behavior. They can help derive patterns and insights which are useful for scientists as well as for greater public consumption.
In this report, I will be reviewing the origins of ornithology with a particular focus on bird migration, its history, various data collection methods. This report will be particularly helpful in understanding the challenges that are faced in the process of data collection for bird tracking and its impact on visualization techniques for bird migration.
Birds have always captured the fascination of mankind. In his book, A Concise History of Ornithology, Michael Walters, talks about how birds’ abilities to communicate and travel in the skies is that makes them distinct . And, there are references to personifying them with supernatural abilities in many ancient myths and religions. The author gives examples of how the Hindu god, Vishnu had the eagle Garuda as his heavenly steed. In fact, in many Native American legends, the Thunderbird is described to be so humongous that it could swallow whole whales and its voice felt like the tempest. Additionally, the Egyptians of the ancient times saw God Horu as a gigantic falcon whose wings stretched from one end of the universe to the other. Birds also appear in a semi-mystical guise in old stone-age paintings in the caves at Lascaux, France. In some instances, they can be of use in historical documentation of the birds themselves. For instance, from the frescos in Egyptian tombs (fig 2.) we can observe that the Red breasted Goose (Branta ruficollis) formerly wintered in the Nile delta, although they no longer do so. However, there have been debates questioning the authenticity of these paintings, only reinforcing the relevance of studies related to our ornithological cousins.
This very continuing fascination towards birds has developed into the mature field of Ornithology. Ornithology as a research domain dwells into the concepts related to evolution, behavior, and ecology of birds including the definition of species, the process of speciation, instinct, learning, ecological niches, guilds, island biogeography, phylogeography, and conservation.
History of bird migration
Origins of bird migration date as back as the eighth century BC. Written records for migration have been found from the ancient Greek scholars, including Homer and Aristotle . Homer, in his epic, Iliad, talks about cranes being at war with pygmies at the ends of the world, pointing towards the possible movement of these birds. Four hundred years later, Aristotle proposed that cranes might have migrated from the Scythian steppes (north and east of the Black Sea and the Caspian Sea) to the headwaters in modern-day Egypt. It is believed that Aristotle brought ornithology to mainstream science by providing a scientific description of bird migrations listing 140 species . However, Aristotle also initiated the long lasting myth that swallows and other birds hibernate in the winter this story was believed by some europeans till the nineteenth century. He also incorrectly noted that the Common Redstart (a common summer visitor to Greece) transformed into a European robin during fall. This was probably due to the disappearance of Redstarts at the same time Robins appeared in Greece. We now know that Redstarts migrate south from Greece to sub-Saharan Africa, while Robins arrive in Greece from the mainland Europe.
Similarly, there are references of bird migration in the Bible, Job 39:26 and Jeremiah 8:7. Jeremiah mentions the seasonal movement of birds -
“Even the stork in the sky knows her seasons
And the turtledove, swift, and crane
Keep the time of their coming.”
Pliny the Elder, a Roman writer of the first century BC repeated many of Aristotle’s writings on the subject. Meanwhile, the myth of bird hibernation grew in Europe. Olaus Magnus, bishop of Uppsala in Sweden, told his readers that both fishes and swallows hibernate in the mud in winters. In fact, in his book A history of northern nations he has a woodcut (from 1555) of a fisherman catching both fish and swallows (fig 3.).
These notions have long hindered improvements in the way bird migrations were studied. For instance, as recently as 17th century, Francis Godwin (1640) and John Wilkins (1703) both defended the idea that birds migrate to the moon. It is possible that this idea originated from what we call today as ‘moon-watching’ an act of observing nocturnal migration of birds against a full moonlight.
We can observe that there is a lack of consensus on bird migration. This was probably due to a lack of scientific methods to measure bird migration.
The eighteenth-century ushered more scientific explorations on why birds disappear during autumn. Von Pernau in 1702 defined migration as it is known these days, the seasonal movement of birds. He described the reason for migration to be an intrinsic restlessness in birds which tells them when is it the correct time to migrate. Carl Linnaeus listed 500 species and initiated a modern approach to natural history studies and is called the “father of modern taxonomy”. In 1822, evidence of long-distance migration came in the form of a white stock which was spotted in central Europe with an arrow of African origin embedded in its neck. 25 such storks were spotted after that and were called Pfeilstorch, German for “Arrow stork”.
Direct field studies of migrating birds began in the nineteenth century. Arrival and departure dates of birds were marked and observations like species, their behavior, count were made. The second half of the nineteenth century saw the founding of ornithological journals and unions like the World Ornithological Congress. Their first congress was hosted in Vienna 1884 with coordination of migration as one of its primary agenda. This gave access to the world of ornithological knowledge and helped collect migration data of birds that fly across countries and continents. The origin of journals would have also encouraged independent rational inquiries across various domains of ornithology.
In the following sections, I have reviewed different measurement methodologies enabling data collection on bird location, distance traveled, speed and physiological data such as heart rate. These are methods described by Mark Denny in his book, Long Hops, Making sense of Bird Migration.
Ringing, also known as bird banding was started by Hans Martensen in 1890s by attaching zinc bands to birds. It started as a method to recognize migration destinations and bird routes. Small birds are trapped in mist nets, funnel traps or cannon nets so that they can be ringed. The bands are very light (they can weigh 0.04 grams) and are made of aluminum these days. The US Bird Banding Laboratory has twenty-three standard sizes of bands for small birds like hummingbirds and large birds like Trumpeter Swans. The bands are designed such that they fit snugly in the legs and don’t hamper the bird’s flight as that could bias the collected data/observations.
Some bands are made of colored plastic that can be read by a telescope eliminating the need to trap the bird again. The colors are such coded such that the bird can be uniquely identified. For instance, a US band will read “Write Bird Band Laurel MD 20708 USA” and “CALL-1–800–327-BAND”, plus a number unique to the band. Any individual, upon finding the bird (dead or alive), can call in with the information. If the bird is alive, it is left in place, else returned. For international bird travelers, international organizations work together to maintain a bird census of migrating bird species. For instance, the US Bird Banding Laboratory works closely with Canadian Wildlife Service and Mexican banders.
Banding can provide various important information like the longevity of birds and their migration routes. For example, a house sparrow banded on July 11, 1989 in texas was found deceased around 2016. An Artic Tern chick banded in Great Britain in 1982 was spotted in Australia, which is on the opposite side of the world, three months later. This suggests that banding is a useful method to observe the life and travel of birds.
The counting method refers to physically counting the birds using visual or audio aids. Birders often spend hours at a given location and keep a note of their bird observations. These observations include a point-in-time count of birds seen at a particular location on earth. There are estimation methods like counting the first ten birds of a large flock in flight and then multiplying it by in proportion with the size of the flock . Bird counting does not cause any harm or interference to the bird populations. Sometimes when the bird is not visible, the sounds are recorded and processed that can give an estimate of the number of birds in the area.
Some birds like raptors are difficult to capture and band, and therefore, direct observation is easier and cheaper for them. Observers pick strategic locations like flyways, stopover sites, and other migration hotspots. This, however, brings a statistical complexity by creating an inherent bias in the observation due to the chosen counting sites. For instance, consider a situation where a species is passing near the observation site which may not be captured at all as is it not visible to the birder.
In the early days, birds were shot down by bullets in large numbers in order to get a count. It did provide a lot of information on birds which were not easy to identify visually. However, this method, by the virtue of its very nature, was not the right way to gather getting census data. Today, ornithologists study birds that have died due to other causes but birds are not killed for census purposes.
Mapping refers to dividing the land into subdivisions (viz. continent, country, estuary, field) and then counting for that subdivision. Mapping requires large manpower to cover large areas.
Moonwatching is another counting method in which a number of nocturnal birds can be observed flying in front of the moon in a near-full moon or full moon night. The fact that it only works during full moon nights is a limitation.
In recent times infrared detectors are being used to observe birds. Birds give out body heat, which can be captured (fig 4 ). This, however, has to be noise-free so that other objects like bats and planes are not captured. This process can be automated to capture continuous shots and can prevent observer fatigue. This method, however, can only count the number of birds and cannot be used to differentiate between the species.
Today, there are multiple citizen science (also known as crowdsourcing or human-computation tools) mobile and web apps that allow people to log bird sightings in their neighborhoods or surroundings of interest. These can be logged with their phones along with the species, count and pictures at a given geo-location.
eBird is a web and mobile application developed by Cornell Lab of Ornithology that allows citizens to log their bird sightings from across the world. They use this data to create visualizations that are accessible for eBird users as well as other viewers to refer to for information of interest. In the diagram below (fig 5), ornithologists use the eBird data to visualize the migration of 118 species in the cyclic seasons. The visualization on the left only displays an animated trail for all species colored by the month they are traveling in. In addition, they have an accompanying visualization, which has the species marked on a moving dot and the index of the species name as text below. Although an interesting way to pivot the visualization based on the seasons, the index visualization is rather difficult to comprehend (which is also pointed out by some of their readers). Not only do some of the numbers overlap making it difficult to read, but the index is also a long list that needs to be scrolled back and forth causing usability problems.
eBird also has an interactive website that has visualizations created by using eBird datasets from across the world. When a user opens the eBird website, they can explore to see the different visualizations. The first one is called the species map (fig 6) which visualizes the various species on a geographical map. However, it does not use a traditional choropleth map, rather it uses a square heat map to show the density of species. This particular design prevents the visual biases that can appear due to geographical sizes in choropleth maps. The design, however, restricts the user to type only one bird species at a time. The search bar for typing the species has a drop-down list, which does not appear until the user types a name. This limits the explorations for users who are not aware of the names of birds and are here to explore the map freely. There are additional filters which allow the selection of time and location to further narrow the search for different species.
The second dashboard called explore hotspots (fig 7), visualizes the same kind of heat map showing the various bird sightings. When the user clicks on a section of the hot spot, they are navigated to a drill-down view which shows all the sightings in that area using colored (based on a number of species observed) pins (fig 8). When the user clicks on any of these they can see the data for that location in the form on another drill down on a list. One of the drill downs from this page presents the species count for a given location (fig 9). This page encourages birders by showing recent visits (most recent data logged) and top eBirders who have contributed data to the eBird database. This could be a step in bringing together the like-minded birders to collate quality data on birds. In addition to the species, one can also drill down into bar charts which show the frequency of count for each species.
Journey North is a citizen science initiative for children and the general public. The project has broad participation, with over 60,000 registered sites in the US, Canada, and Mexico -including families, teachers, schools, nature centers, professional scientists and novices. The events are with species such as instance tracking hummingbird migration. Their website has a view maps section that takes the user to a visualization that maps all of the bid sitings for a given time. It also has a playing time slider which shows us the location of sightings and how their number increased over time (fig 11). Participants log sightings by following simple protocols and can mark sightings from the field, view maps, take pictures, and leave comments on their blogs (fig 12).
Radio transmission, developed after the world war II, allows remote monitoring by attaching a transmitter to its tail feathers (for a large bird) or as a bag pack (for smaller birds). This allows measuring parameters including altitude, length of individual flights, flight speeds, stopover duration and other behaviors that cannot be individually be observed (like behavior or partial migrants, individual birds at communal roosts and disposal of juveniles from breeding grounds).
This method became useful for ornithologists after 1980s. It was only after this that the transmitters were lightweight enough that they could be attached to birds without significantly hampering their movement. This is, however, a costly method. Each radio transmitter can cost up to $3000. Along with this, comes the cost of installing receivers on cars, planes, and satellites and handling the logistics of long-distance international migration.
Today, radio tag (called Platform Transmitting Terminals (PTT)) (fig 13) come in various sizes for different birds. The heaviest ones weight no more than 100 grams and has a range of several kilometers depending on receiver sophistication and life of two-three years.
Many species, even small ones like the Western Sandpipers, have now been radio tagged and tracked on their migration journeys. In 1992, several small shore birds were tracked on a 4000 km journey from California to Alaska. Their movements were tracked by receivers on the ground and in the air. It was observed that they made a series of short hops with layovers of two-three days in between to stock on food.
In another study, the PTT attached to Swainson’s Thrushes measured the heart rates, wing rate frequencies, and respiration rates of free-flying birds. It was observed that these birds use twice as much energy in stopovers as compared to the actual migratory flight.
If the radio has enough power, signals can be caught by a satellite which is much better than keeping track from the ground because of complete coverage. Satellite tracking is done by the ARGOS system of satellite receivers. These systems are aboard five satellites belonging to National Oceanic and Atmospheric Administration or European Organization for the exploitation of Meteorological Satellites. These are in a polar orbit which means they pass over the poles on every orbit.
Each PTT sends a unique signal to the ARGOS satellite. Each signal contains the transmitter frequency, rate of repetition and signal content (including PTT ID number). This is enough to identify the transmitter location with an accuracy of 15mts. The satellites then transmit this data to forty ground locations where this data is further calculated to give the exact coordinates. A series of data can give the migration path. Satellite tracking of birds has become an industry today.
One of the studies tracked a Peregrine Falcon called ‘Island girl’ was tracked on her 2010 migration. It took her fifty days, from April 13 to June 2 to travel from Santiago in Chile to the Baffin Islands in Canada. The journey was 8900 miles(14322 kms). This allows us to experience migration in real-time rather than rely on sporadic inputs from counting studies.
Satellite tracking is able to capture the spatial-temporal pattern of migration details including length of each day’s flight, altitudes at which the bird flew, location of staging grounds and duration they paused on these grounds. However, satellite tracking is helpful in tracking only large to medium-sized birds as the smaller birds life a rather weak PTT signal. Efforts are being made to make the reception stronger.
In the documentary, Migrating Birds: Scouts of Distant Worlds on Amazon Prime . They not only track the migration of selected families of storks and geese but also discuss how the overall migration looks like across the world using a mixture of animation and video. They note many birds are either able to survive the harsh conditions of migration or are caught in man made traps (fig 14). They also have body sensors on the birds which give out data like their heartbeat and wing movements. They talk about how the birds use the wind thermals to help boost their flying with minimal exertion (fig 15).
Geologgers (fig 16) are smaller and lighter than PTT and can be installed easily on small birds. They work by capturing the light levels between the sunrise and sunset. Using this data a calculation can be made within 40 miles of the latitude and 100–200 miles of longitude.
Geologgers store this information thus they need to be retrieved in order to access the information. This makes this method feasible for site-loyal birds like Pacific Golden Plovers who migrate to Hawaii during winters.
Bird observation using the radar occurred for the first time in 1940 during World War II when a British radar detected a flock of geese instead of German planes.
The radar data is very different from satellite telemetry because it consists of a signal transmitter, receiver as well as a signal processor. The transmitters transmit the frequency at an appropriate wavelength the meteorological data is then removed from the received signal to reduce noise. A radar sends out microwaves which are reflected from the object. A part of this reflected radiation is received and displayed on the radar screen. For an airplane, it can give information like the distance, speed, and bearing of the source. However, in case of birds, they are usually observed as a flock because radars are sensitive to the size, composition, and orientation of the source object. An individual bird will be extremely difficult to observe due to its weak reflected signals.
An operator can differentiate a flock of birds from a flock of insects or dust is by using doppler processing which can the speed of the object. Birds can fly faster than the wind and in the opposite direction as well which makes them easier to identify. In the United States, Radar ornithology is assisted by the National Atmospheric and Oceanic administration’s 157 weather radars located across the United States.
Radars are particularly useful in observing nocturnal migrants. The screen blooms dramatically when a flock passes through it range (fig 17). An expert ornithologist can identify the characteristics of a bird flock, for instance, the edges for a bird flock are softer compared to meteorological features, the shape is also different as they form a donut-shaped visualization which changes to a crescent as they move away. If birds appear at a roost site and disperse in the search for food, they can appear as an expanding circle.
Table 1: Summary of different types of data collection methods used to study bird migration:
Significance of Bird Migration Visualization
Bird Migration visualizations are of importance to the scientific community as well as for general public consumption. They help to visualize complex patterns of bird movements across the world which can have an impact on various fields such as conservation, climate change studies.
Community and Scientific Outreach
Bird migration charts capture the attention of expert ornithologists and common citizens alike. They have been a great source of knowledge on various applied fields like climate change, habitat conservations, bird conservation to name a few. There are efforts to combine the power of technology and the manpower of citizens to work towards providing a conducive environment for counting birds as they take up perilous migrations. Audubon and Bird Cast, by the Cornell Lab are two such communities. Bird Cast is a project which combines the might of the Next Generation Radar (NEXRAD) along with volunteering bird watchers to keep a track of a database of bird data (fig 18).
Education and awareness
It is observed in most bird watching experts, there is an enthusiasm to educate younger generations and school children about birds and bird watching practices. They want to inculcate a sense of responsibility in the children so that they grow up to be sensitive adults and treat the environment and everything it contains as their own. Needless to say, there are a lot of examples of bird migration visualizations in the print medium like posters, bird migration encyclopedias and birding handbooks. National Geographic has a collectible poster that can be used for educational purposes or as a birder’s collection (fig 19). Another book is the Atlas of Bird Migration: Tracing the Great Journeys of the Worlds by Jonathan Elphick. It contains illustrated maps of migration for various bird species (fig 20). The book, The Art of Migration by John Bates, James H. Boone and Peggy Macnamara uses artist Peggy Macnamara’s watercolor art to tell visual stories of bird migration (fig 21).
These two maps in (fig 22) are from a bird migration article by National Geographic. It contains interactive maps (using the ebird database) for various bird species in the American continent. The first map (left) shows the routes taken by particular types of species. It can be observed how each species tries to stick to their habitat as much as possible when they are migrating. The second map (right) is for the Western Tanager which migrates at night. The map is a playing video that allows you to see the movement in action and one can click on the circular arrow button pauses so that one can see the nearby geographic references for each season. The designer uses a monochrome gradient to show the number of species in the map using an earthy brown palette.
This motion map (fig 23), created by Dan Majka, an analyst at the Nature Conservatory, tries to visualize corridors that birds, mammals, and amphibians are likely to take with projected climate change in the next 70 years. He uses an interesting neon-colored trail for each animal. This map shows that in spite of urbanization there are routes animals can take as the earth gets warmer. This map tells us which corridors we will need to preserve to maintain an ecological balance if we don’t want to disrupt these migrations.
One of the primary reasons why bird migration is important is because of its impact on many related fields like climate change, bird conservation, habitat studies, and policymaking to name a few. Interestingly this rather interesting and important phenomenon was not visualized for a long time in history. This was because collecting bird data is a rather difficult task and scientific methods are only a century old. There are multiple methods but they all come with their limitations. There is a need to coordinate internationally with various agencies. It is thus also important to have enough bird literate citizens who can lend a helping hand in various bird census efforts.
I would thank Ms. Bahare Sanaie-Movahed, GIS specialist at Northeastern University for helping me understand the concepts of GIS mapping.
- Walters, M.(2003), A Concise History of Ornithology
- Danny, M.(2016), Long hops: Making sense of Bird Migration
- Mayr, E. (1984). Commentary: The Contributions of Ornithology to Biology. BioScience, 34(4), 250–255.
- Bibby, C.J. (2003). “Fifty years of Bird Study: Capsule Field ornithology is alive and well, and in the future can contribute much more in Britain and elsewhere”. Bird Study. 50 (3): 194–210. doi:10.1080/00063650309461314.
- https://www.ancient-origins.net/news-history-archaeology/painting-considered-masterpiece-ancient-egypt-may-be-1870s-fake-002851, Accessed on: 7:45 PM (EST), December 2, 2018
- https://www.allaboutbirds.org/the-basics-how-why-and-where-of-bird-migration/, Accessed on: 7:45 PM (EST), December 2, 2018
- https://ebird.org/news/counting-101/, Accessed on: 10:17 PM (EST), December 4, 2018
- Migrating Birds: Scouts of Distant Worlds by Petra Höfer, Freddie Röckenhaus on Amazon Prime, Accessed on: 8:00 PM (EST), December 4, 2018
This report was first written for the Information Design History cour taught by Prof. Paul Kahn at the Information Design and Visualization(IDV) program at Northeastern University, Boston.