Due to the recent popularity of butterfly releases, some questions have arisen about how this activity might affect the native wild population. This study in particular will address the question about how the release of lab-reared monarchs into the wild affects the ability of the butterfly to navigate during the fall migration. We released 5,343 monarchs in various western states starting on September 16, 1999 and ending on October 19, 1999. We were pleased to find out that they do indeed migrate. All of our monarchs were 8th to 9th generation lab-reared from 120 original wild caught monarchs. Even though there was no exposure to the wild-caught gene pool, that they were reared in lab conditions, and that they were transferred and released far from their natal origin, they were still able to navigate along with the wild population.
The purpose of this experiment is to broaden our general understanding of the ability of a laboratory-reared monarch butterfly (Danaus plexippus) to navigate during the fall migration. This information is important because of the recent increase in activity of transfers and releases of commercially-reared monarch butterflies. With this activity came the claims from some butterfly conservation groups, such as The North American Butterfly Association (NABA), that the mixing of lab-reared monarchs and the wild population could cause the failure of the butterfly to migrate. NABA writes:
"Now imagine tens of thousands of mixed-up Monarchs unable to find the way to their overwintering grounds. This depressing image may become a reality if the rapidly-growing fad of releasing butterflies, including Monarch butterflies, at weddings, state fairs, and other public events continues to spread. Because the released Monarchs may have come from California, for instance, where they do not migrate to Mexico, their offspring may not be able to orient properly. Because the Monarchs were raised inside under unnatural conditions, it is possible that their delicate migratory physiology may not have been turned on."
Unfortunately, NABA does not cite any scientific studies that would lead to the above conclusion, so we had to simply use the claims in the above paragraph as our springboard. Out of the expressed concern, we ask the question, "Do laboratory reared monarchs migrate?" We believe that if this question can be answered scientifically, we can relieve the concerns that NABA brings to the table.
But, this data only provides information for up to 2nd generation monarchs. Many commercial breeders rear anywhere from 2 generations all the way to 9 generations without any exposure to the wild population gene pool. So, we concluded that the Monarch Watch information alone would not be sufficient to confidently answer the question. We decided to design this study around the most extreme case of inbreeding and lab rearing in order to see if these factors had any affect on the migration. So, we chose to use 8th to 9th generation lab-reared monarchs in order to provide data for the "worst case scenario."
During the months of September and October of 1999, we planned to produce approximately 1,200 extra butterflies per week at our Western Swallowtail Farms facility in Woodland, CA. So, the butterflies that would eventually be tagged and released came directly out of our normal release stock. No extra care or special rearing arrangements were made for this livestock except for the addition space, materials, and labor needed due to the increased production.
Once the butterflies emerged and were released into the flighthouse to be staged for shipping, they would be ready to be tagged. For each week that we were to ship tagged butterflies, we had a special crew come in specifically to do the tagging, packaging, and shipping. Typically, the butterflies were to be shipped on Wednesday of each week. The tagging would be done on Monday and Tuesday prior to shipping. Each day we would tag approximately 600 butterflies to be released back into the flight house. We used the Avery round neon red tags that are ½" in diameter. Each tag is marked with an individual serial number and a standard toll-free contact number using indelible ink. The tags are "trimmed" along the top and bottom in order to slightly reduce the weight of each tag. Each butterfly carries two tags; one tag on each of the hind wings. The tag is adhered to the wing using standard rubber cement. On the shipping day, the butterfly is placed into a small triangular shaped box, and then 200 of these are placed in a larger shipping container that is insulated and cooled. The butterflies are kept in good condition while in transit using this method.
· On September 15, 1999, we shipped the following under USDA permit numbers 35485 & 35486:
· On September 22, 1999, we shipped the following under USDA permit number 35486:
· On September 29, 1999, we shipped the following under USDA permit number 35462:
Quantity Serial Numbers Location FedEx tracking number
· On October 6, 1999, we shipped the following under USDA permit number 35462:
· On October 19, 1999, we released the following (no USDA permit necessary):
Please see the Master Tagging Report for the actual data and the North American map for a visual of the estimated flight paths. A total of 36 monarchs were recaptured and validated. There are, supposedly, another 2 dozen tags in Mexico that have yet to be identified. Since we are unable to locate them and validate the serial numbers, we can only use our current confirmed data. Nevertheless, the 36 recaptures that we did get will provide a significant amount of data to come to some reasonable conclusions.
1. Local release.
Our first significant finding from the local release is that lab-reared monarchs certainly do migrate after being transferred to a short distance away from their natal origin. Our local release in Placerville, CA greatly exceeded the historic standard recovery rate of ½ % (average recovery rate for the last decade of tag and release published statistics). Out of the 600 monarchs released, we needed at least 3 to be recovered at an overwintering site to be consistent with known averages. We had 20 recoveries which is more than a 3% recovery rate (6 times greater than the average). It was no surprise that we had a high recovery rate due to the short travel distance. But, this data does show clearly that the lab-reared monarchs were able to navigate properly after being released a short distance away from their natal origin.
2. Ability to navigate after a long distance transfer.
With the data starting to come in from the local release, we had hope that we would soon start getting recaptures from the distant releases. Sure enough, this came to pass. From the releases in Evanston, WY on September 16, 1999, monarch #Y137 was found near Chrome, CO, which was clearly on it's way to Mexico (see map). Monarch #Y114 was found in Manifee, CA, which is very close to some of the Southern California overwintering sights. From the releases in Paonia, CO on September 16, 1999 and September 23, 1999, monarch #R259 was found in Amistad, NM, clearly on it's way to the Mexican overwintering sights. From the releases in Albuquerque, NM on September 30, 1999, a total of 8 monarchs were recaptured, both at and on the way to overwintering sights in California and Mexico. Finally, from the releases in Silver City, NM on October 7, 1999, 2 were recaptured in Mexico (#X556 and #X549), one on the way to California (#X238), and the other at a California overwintering sight in San Diego (#X184).
3. Migration direction does not necessarily depend on natal origin.
The next significant finding so far is that we have recoveries at both the Mexican overwintering sites and the California overwintering sites from one single release. For example, monarchs #M267 and #M274 were recovered in Ventura, CA and Goleta, CA, respectively, at the local overwintering sites. Monarch #A314 was recovered at the Cerro Pelon overwintering site in Michoacan, Mexico. All three of these butterflies were released in Albuquerque, NM on September 30, 1999. This data could also indicate that the Mexican overwintering sites are not strictly composed of monarchs from east of the divide and vice versa. Please see the map for a visual of how the monarchs clearly travel in both directions.
4. Wide dispersion.
From these releases, we have a dispersion range from the California coast to Lenora, KS (#R170). This range is over 1,200 miles from a general release location along the Continental Divide. From one release alone, in Albuquerque, NM, we have a dispersion range close to the same distance of 1,200 miles. Monarchs #M267 and #M274 were recovered along the California coast and monarch #A314 was recovered in Mexico. With dispersion that is this widespread, it is inconsistent to believe that isolated genetic populations evolved to form an eastern specific and western specific subspecies.
Map of North America
We have learned that lab-reared monarchs behave similar to wild monarchs in terms of migration behavior. Therefore, we believe that we can confidently answer "yes" to the question of whether or not lab-reared monarchs can navigate during the fall migration. But, we also answered another question about gene flow between the western and eastern breeding populations. Seeing how some of the monarchs ended up at both the Mexican overwintering sites and Californian overwintering sites from the same release, we can conclude that the monarch disperses and mixes enough during the migration to completely homogenize the two breeding populations. With this concept, we can conclude that it would be impossible for any genetic isolation to occur within the entire population. If any isolation did occur during the breeding months, it would then be wiped out from mixing during the fall migration and breeding at the overwintering sites.