Monarch Watch Directional Flight Project

2023 project page updated 12 January 2023.

OBSERVATION PERIOD: 22-May through 16-June; the recording period for each latitude range is 10-11 days (see below)

NOTE: We will send an email to all registered participants with a link to the actual submission form after the observation period comes to a close (June 16th). If you have not yet registered, please do so via the link below. Thank you!

Monarch Watch is seeking the immediate assistance of monarch enthusiasts (community scientists) in collecting directional flight observations of monarchs in their area during the spring migration.

BACKGROUND - by Chip Taylor

The Spring Migration: when does it end?

Several years ago, we posted a project for students and groups interested in the monarch migration entitled Flight Vector Analysis. It was our hope that folks would follow the instructions and learn how to track and record flight directions for different regions of the country. There are a number of questions about monarch orientation and migration that would benefit from a rich vein of field observations along these lines. Unfortunately, to the best of my knowledge, this project did not generate a lot of interest. However, this page and project is now relevant in the context of the recent puzzle and associated quest to determine when the migration northward by first generation monarchs stops at each latitude. Below you will find a reboot of the earlier directive. The version below is a bit simpler and limits the observation periods for each latitude to a 10-11 day interval. The data from this project constitute a test of the hypothesis that the migration stops when the increase in daylength declines to less than one minute at each latitude. As explained in the monarch puzzle wrap up, the hypothesis is based on two observations that are suggestive of a pattern, but both are weak in that they are not represented by data. Both could be wrong, which is why we need data, and why we need citizens to help us by documenting directional flight in May and June.

Directional flight/migratory flight

Directional flight - a straight line (linear) flight to a point on the horizon.

During the spring and mid-summer migrations, there are powered directional flights with no gliding and soaring. Most flight is rapid at speeds of 10-12 mph at 4-10 meters above the ground. Nectaring occurs mostly in the morning and late afternoon. There is some mating and egg laying as these migrations progress. These migrations appear to advance at rates of 30-55 miles per day. In the spring, there are two generations of migrants, the monarchs returning from Mexico have headings that are primarily to the N and NE. This migration generally ends with the death of most of the overwintered monarchs by the end of April. The offspring of the overwintered migrants begin to reach maturity at the end of April and they too tend to move to the N and NE. It is these first-generation monarchs that recolonize the northern breeding area. Curiously, this migration appears to stop at different latitudes as the season progresses northward. This observation gives rise to several questions: do they stop and, if so, when do they stop and why?

Directional flights are linear and have a compass heading that will take them to a distant point on the horizon, which distinguishes them from meandering flights associated with searching for nectar, host plants or mates. These headings can be measured by positioning oneself behind a passing monarch and aligning a compass along the long axis of the monarch's body. These readings indicate the direction the monarch is attempting to maintain. Observers can also measure vanishing bearings - the point on the horizon where the monarch disappears from view. The headings and vanishing bearings can be similar when there is little or no wind but can differ substantially if there are strong quartering winds that strike the wings obliquely. In the fall, given the prevalence of winds from the SW, monarchs tend to be displaced to the SE of their true heading. Displacements can also occur to the SE following strong fronts from the NW. In contrast, in the spring, a monarch headed to the NE on a heading of 40 degrees could drift further to the NE if the winds are from the W, N, NW or conversely to the NW if the winds are ENE or SE. In both of these cases, the vanishing bearing - or point on the horizon where the monarch is lost from sight is to the right or left of the intended compass direction as indicated by the long axis of the monarch's body while in flight.

While both measures tell us something about how the monarchs are progressing toward an objective, the headings provide information on the cues monarchs use to set a course. These directions may represent a response to the earth's magnetic fields, e.g., magnetoclinic orientation*. Along these lines, it is important to point out that there is no evidence that monarchs compensate (by crabbing) for quartering winds as pilots have to do when landing planes in a cross wind (see "How Planes Land Sideways In High Winds" video).


See also: Guerra, P., Gegear, R. & Reppert, S. A magnetic compass aids monarch butterfly migration. Nat Commun 5, 4164 (2014).

Where to observe directional flight

Directional flights are best observed in open spaces such as sports fields, pastures, grassy fields, etc. The areas should be relatively flat and the distant (100 meters or more) horizon should be open at least 30 degrees to the right and left of N. You will want to position yourself facing N so the butterflies are flying over your shoulder. You may have to move about the space a bit to see the butterflies coming up behind you and then moving to align yourself behind the butterfly as it moves away from you. I have found that these flights are easiest to observe under cloudy and partly cloudy conditions. While flights tend to be low when temperatures are at a minimum early in the day, most flights later will be at 4-10 meters which makes them both hard to see and hard to track. Recording this behavior will be a challenge and will require some patience.

One way to increase the probability of seeing and recording these flights is to locate large patches of milkweeds or flowering plants that attract the passing monarchs. If they stop to lay eggs or visit the flowers for nectar, watch them carefully and record their headings when they continue their journey to the N, NE.

What to do when you see linear flights

If you see linear flights, do your best to align yourself behind the line of flight. It's best if the butterfly is headed directly away from you so that you are looking at the same horizon the butterfly is headed toward. Then use a hand-held compass or the compass on your mobile phone and align the needle so that it lines up with the long axis of the monarch's body. That measure represents the heading. Next, record the vanishing bearing - the compass point on the horizon where the monarch disappears from sight. The latter tells you how much each butterfly is being displaced by the wind. The two measures tend to be similar when there is no wind but differ depending on wind direction and wind speed. Both should be reported as degrees from North (clockwise).

You won't be able to align yourself with every butterfly. Some will be too far away to see the axis of the body. That's ok. Like most things, taking these measures accurately takes some practice. Also, don't expect every butterfly to do the same thing. When summarizing the data, you may find that headings vary as much as 30-40 degrees and vanishing bearings even more. That's to be expected given that you are estimating the compass directions, and there is some variation among the monarchs themselves in their orientation. What you are looking for are mean headings for 20 (or even a few) or more monarchs under a variety of conditions at your location(s).

When to watch for directional flight

Most directional flights occur between 9AM-4PM (daylight time) when temperature and wind speeds are favorable. Temperatures during fall migrations usually range from 60-85F with the greatest numbers observed when the temperatures are in the low part of that range. The opposite seems to occur during the spring and mid-summer migrations with most flight occurring when temperatures are in the higher portion of that range. Wind speeds of less than 10 mph favor flight. Higher wind speeds, especially if coming from directions that shift the butterflies strongly to the right or left, increase the difficulty of getting accurate readings on the headings the butterflies are trying to maintain.

How many can I expect to see?

Frankly, I have no idea. There could be lots of zeros or you might see 10 per hour at the peak of the northward migration. To determine if any monarchs are passing through, I've laid down in a position where I could scan the skies for any butterflies coming from the S. Once I established monarchs were on the move, I could prepare myself to track the monarchs as they progressed to the N and NE. While these sightings can be carried out by individuals, this could be a team project as well. It certainly helps to have more than one pair of eyes looking for passing monarchs.

Recording data

To record the data, you can use the data sheets below or you can create your own. For each butterfly, it is useful to record the date, time of day, heading, vanishing bearing along with wind speed and direction. It's also useful to record whether the observation occurred under clear (full sun), partly cloudy or cloudy conditions. Or, better yet, watts per meter squared - a measure of the intensity of the solar radiation. The latter is important since it factors into the heat balance the butterfly tries to maintain. The weather data can be obtained from your own weather sensors or a nearby Weather Underground weather station (see below).

There are links below to download the Directional Flight Datasheet in Excel format (to enter data into the spreadsheet) or PDF format (for printing), both of which contain the following fields to enter your observational data:

Field Type Description
Observation # number enter in numerical order
Date date enter in mm/dd/yy format
Time time enter in hh:mm am/pm format
Heading number enter as degrees (clockwise from North)
Vanishing Bearing number enter as degrees (clockwise from North)
Temperature number enter as degrees F
Wind Speed number enter as mph
Wind Direction text enter as N, SW, NNE, etc.
Solar Radiation number enter as watts per meter squared
Cloud Cover text enter clear, partly cloudy, or cloudy

Please note that not all of these fields are absolutely required, just try to enter as much information as you can.

Weather Underground

Weather Underground is a global community of people connecting data from environmental sensors like weather stations and air quality monitors to provide access to hyperlocal data. If you do not have your own station to provide the weather data above, you should try to locate one nearby. Once you identify a station in your area, you will be able to monitor weather data in real time or view historical data.

As a starting point, please visit Monarch Watch's Weather Underground weather station dashboard then zoom in and out of the map on that page to locate a station in your area. On the dashboard page you will see graphics that report current temperature, wind speed and direction and solar radiation, all under the title "PWS CURRENT CONDITIONS".
Below that, you will have access to the Weather History and if you move your cursor along the graphs provided you can see values for a particular time of the day that you can add to your observational data. You may also switch between graph and table views via the navigational tabs (table view might be a little easier to use to retrieve your historical weather data at the time of your observation). Please note that data is reported in 5-minute intervals so simply choose the time closest to the observation time you recorded. To view data from another day, use the "previous" and "next" arrow icons or select from the dropdown menus and click on the "View" button.

Recording period

For the spring migration, the recording period for each latitude range is 10-11 days. The expectation is that the migration will diminish to zero at some point during this interval at your location. To locate your latitude, go to or (there are lots of different ways to identify your location). The intervals for which observations are needed for each range of latitudes are given below.

Latitude Beginning Ending
29-31 22-May 1-Jun
32-34 26-May 5-Jun
35-37 28-May 7-Jun
38-40 30-May 10-Jun
41-43 1-Jun 11-Jun
44-46 4-Jun 14-Jun
47-49 5-Jun 15-Jun
50-51 6-Jun 16-Jun

Reporting data

If you succeed in making observations of directional flight, even if you haven't determined when flight ends, please submit your data to us in June via the online form. We will send all registered participants a link to this form after June 16.


Here is what we need you, as community scientists, to do:


To determine your geographic coordinates, please use one of the following sites (or others) to enter your city, state/province, and zip/postal code and retrieve your latitude and longitude in decimal form (for example, latitude: 38.93 longitude: -95.29 for Lawrence, KS 66047).

Register as a participant in this project (even if you registered previously) by providing your name, location (including latitude and longitude), and email address via the form at


We have provided some sample files that you can use to log your observations but exactly how you do it is up to you. Please feel free to use whatever is easiest and most comfortable for you to log your daily observations of monarch numbers - you will then use this log to complete a simple online form at the end of the project period.

Excel format: directional-flight-datasheet.xlsx (to enter data into a spreadsheet; can be imported into other applications)

PDF format: directional-flight-datasheet.pdf (for printing)


Submit your data to us at the end of the project period via an online form. We will email a submission form link to the email address you give us when you register. The form will be simple and allow you to enter your data using your notes. There will also be an option to upload your completed spreadsheet.

We will assemble the records and then provide summaries online once we have a chance to analyze the data.

Please register for this project and start logging your observations today! Thank you in advance for your assistance - if you have any questions or comments about this project, please contact us at

Photo credit: "Monarch Flight" by TexasEagle is licensed under CC BY-NC 2.0.

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