woodcreeper

The next full moon is November 2nd, so get out your scopes and let’s do some moonwatching! Starting on October 29th and going until November 6 we’ll be coordinating our next moonwatching event. Please read the description below for background, instructions, and links to the datasheets and electronic spreadsheet for submitting your observations. If you’re planning to participate, please send me an email (moonwatch@woodcreeper.com) so we know that we can count on you. This time of year we can see large flights of short-distance migrants such as various sparrows, American Robins, Northern Flickers, and Hermit Thrushes, to name a few.

BACKGROUND

In North America and Europe, research has demonstrated that the majority of migrating birds fly at night. The predominant theories explaining why some passerines migrate by night in North America and Europe—to avoid predation, to take advantage of greater atmospheric stability and celestial navigation clues, and to use cooler temperatures to dissipate body heat – could be applied to any other migration system.

Normally, nocturnal migrants fly at heights where they are not visible to us. However, by watching the disk of the full moon with a telescope in spring or autumn, from time to time you can see birds crossing the disk of the moon. The number of birds counted in a given time interval is proportional to the intensity of bird migration. However, numbers are not directly proportional to intensity; observations are influenced by the height distribution of the birds and the visibility according to distance and the position of the moon.

With good visibility and a telescope of 20-30x magnification, nocturnally migrating birds can be recorded at altitudes up to 1500m. With the methods outlined below, intensity and flight directions can be recorded simultaneously.

Normally, one cannot distinguish different species of birds by moonwatching. However, many nocturnal migrants give “flight calls” (short, distinctive, repeated vocalizations) while they are flying. In North America, many nocturnal migrants can be identified to genus or species by their flight calls. It may be possible to identify some migrants by their vocalizations during your observations.

METHODS

Site: In principle, any site can be used for observations, if the moon is visible for the whole observation period. In general, sites greater than 1000m in altitude should be avoided. Also, neighboring sites should be at least 50 kilometers apart.

Equipment: Telescopes with a magnification of 20 to 30 power (30x is optimal) are well suited for observations. Stronger magnifications cause the disk of the moon to appear very large and therefore birds at the edge of the moon are often overlooked. A stable tripod which allows you to follow the path of the moon manually is absolutely indispensable.

A clock or watch is needed to write down the beginning and ending times of the observation periods (in minutes). Also, you will need two or more copies each of the two protocol sheets, A and B and a clip board (preferably with a cover to protect the data sheets).

Staff: Data recording is much easier and more accurate with 2 or 3 people are needed to alternate between watching and data recording (besides, it’s more fun with a friend!). Single observers should record their comments on a tape, or work with a stop-watch alarm to interrupt observation time while writing down the observations.

Period of observation: Observations should take place on clear or only slightly overcast nights within 3 days before or after a full moon, when the maximum number of birds could potentially be observed. During the fall of 2009, observations should occur between October 1-7 and October 31 – November 6. Counts should be performed on each night when the moon is visible and at an elevation of at least at 15-20° above the horizon (if the moon is very close to the horizon, estimations of directions and migratory intensity become very inaccurate).

Data recording & Time commitment: We know you’re busy, and your time is important. Whether you observe for a single night, or for the entire period, any data you provide will be useful. On each night you observe, you should try to make observations either for 200 minutes or until 50 birds are seen, whichever comes first. This is an ideal coverage period, but again, do whatever you can! We highly recommend that each person watch only for 10 minutes at a time to prevent visual fatigue. Shorter observation intervals are possible but the exact duration (in minutes) must be recorded on the protocol. Regular pauses of at least 5 min (for people watching alone) must be made in order to maintain the necessary concentration over a observation period of a few hours. There should be at least 30 minutes (three 10-min. intervals) of actual moonwatching in each hour of observation.

We have designed a data sheet for collecting your data in the field, as well as a spreadsheet for entering your data for submission at the end of the study.  Links to these files can be found by scrolling down to the Data entry section of this page. Please review these and familiarize yourself with the data to be collected before going out in the field (it’s dark out there!).

Remember that it is very important to record time periods even if no birds/bats are detected, as they too tell us something about the level of migration. Please make sure to include them in the data you submit. Generally speaking, Sheet A of the spreadsheet includes the overall site information and general information for each night of moonwatching. On Sheet B of the spreadsheet, you will record the specific  observations of birds passing the disk of the moon. While the moonwatcher is constantly watching the disk of the moon, his or her colleague should record for each observed bird the corresponding time interval, the actual time (not absolutely necessary if single observation intervals do not exceed 10 min.), “in” and “out” directions and the silhouette size of the bird given by the moonwatcher.

Determination of direction: The direction of the bird is given by the point of entrance and the point of exit on the disk of the moon. Point of entrance and exit are given according to the face of a clock. 12 o’clock is at the top of the telescope, 3 o’clock to the right, 6 o’clock at the bottom and 9 o’clock to the left. The direction given by the moonwatcher should be point of entrance to point of exit. For example, in the figure to the left, the tracks (from top to bottom) would be 9-3 (from left to right), or 10-2 (also from left to right) and 9-5 (left to lower right). It is permissible to estimate the point of entrance backwards, because often small birds (far away) are detected just when they are already inside the disk. Please limit points of entrance and exit to whole hours directions only (no “9:30 – 3:15″, please).

Determination of the size: The silhouette size of the observed bird is classified in relation to the size of the most conspicuous crater (“Tycho”) on the lower part of the moon (see figure below). This is just a rough classification; research in the European Alps has shown that normally 80 to 90% of the birds are within the size classes of 1 to 4.

1. very small, just a point, hardly recognizable as a bird, much smaller than the crater
2. ca. 1/4 of the size of the crater – recognizable as a bird
3. ca. 1/2 of the size of the crater
4. ca. the size of the crater
5. ca. double of the size of the crater
6. ca. 4 times the size of the crater
7. very large, mostly fast shadow (out of focus), half of the disk of the moon or more.

It is important that for each bird direction and size is recorded. We know that it is just a rough estimate, but it is still much better than nothing.

The diameter of the crater (“Tycho”) serves as a reference for the classification of the silhouette size of the bird.
The position of the crater turns during the night around the center of the moon, but the distance from the border of the disk keeps constant.

Extra: If you hear flight notes while you are moonwatching, record this in the “remarks” column of protocol sheet A, and try to describe or identify the calls.

An important principle: Give all the required information as exactly as possible at the time of observation; later corrections are mostly very difficult and time consuming and often not possible (e.g. an observation with only the point of entrance is useless). Avoid ambiguities. What you cannot decide on the spot can not be done later at the office desk.

Those doing moonwatching for the first time should write “new observer” on sheet A as a remark. In addition, newcomers must pay attention to the fine points which regularly seem to move over the disk of the moon. Do not count them as birds, because these are almost exclusively reflections of your own iris. There should be no confusion after having seen some real birds passing by.

Data entry: Please download the Microsoft Excel spreadsheet here and the sample data sheet (pdf) here. The spreadsheet consists of four worksheets, two of which are examples of how to fill them out, and the other two are for your data entry. The data sheet is a pre-printed data entry sheet for you to use in the field. Feel free to create your own data sheet to suit your style of data collection, just be sure to include all of the necessary information. Please do not change the spreadsheet, however, as that will make compiling the data more difficult for us in the end. After the moonwatching period is over (October 8 and November 6) please send us a copy of your completed spreadsheet to the following email address: moonwatch@woodcreeper.com. After the data has been compiled, each contributor will receive a summary of the results.

Instructional videos:

Getting Geo Data from Google Maps

Protocol adapted from: “Instructions to count nocturnal bird migration by watching the full moon.” Swiss Ornithological Institute (1996) and “South American Migration Moon-watching Project”. JENNIFER E. JOHNSON, Biol. Dept., Swarthmore Coll., Swarthmore, PA. (2004)

Questions or comments may be sent to moonwatch@woodcreeper.com