Monarch Watch Blog

Post-Storm Status of the Monarch Colonies in Mexico

Tuesday, March 2nd, 2010 at 5:20 pm by Chip Taylor
Filed under Mexico, Monarch Population Status | 3 Comments »

In previous blog posts we have described the conditions during the breeding season that resulted in a small migratory population, provided the report from Eduardo Rendón (WWFMexico) indicating that the overwintering population was at an all time low (1.92 hectares), and expressed concern about the impact of January and February storms on the overwintering colonies.

Anticipating that it would be difficult for Eduardo and others to assess the colonies due to the devastation of Angangueo and the surrounding area, I asked those who were visiting the monarch colonies to report what on what they have seen. The reports below are from scientists, tours leaders, and tourists. Collectively, these reports provide a general view of the health of the colonies but it remains difficult to assess the extent of mortality due to the winter conditions and the size of the population that will be returning northward.

These reports deal with the following colonies (number that follows indictes the area, in hectares, in December): Herrada (0.06), Sierra Chincua (0.47), El Rosario (0.50), and Cerro Pelon (0.53). There is no information on the remaining three colonies, all were small with a combined area of 0.36 hectares.

A Brief Summary

The small colony at Herrada appears to have been decimated by the winter storms and it would be surprising if more than 30% of the butterflies survived at this location. Although significant mortality was reported by one observer at Cerro Pelon, this colony seems to have survived the winter quite well and should send a good proportion of the original population northward over the next 2-3 weeks. The status of Chincua and El Rosario relative to their original populations is difficult to assess. Chincua appears to have far fewer butterflies than in mid-January and the area shows a considerable amount of damage. At El Rosario monarchs are clustered near the entrance to the trail and are flying and mating with the gusto monarchs typically display at this time in the season but the population is so spread out that it is difficult to determine if the colony is intact or just a small remnant of the original 0.50 hectare colony. We are anxiously waiting for additional reports.

The following reports have been edited for clarity and brevity.

Received from Donald Planey late on the 26th of February:

We just got back from Chincua today. We were supposed to do it yesterday, but we got lost so we just ended up going to El Rosario via Ocampo yesterday*. Here’s what I saw both days:

As far as I could tell at Ocampo (El Rosario), the butterflies were doing great. Unfortunately, we couldn’t see all of it, because the people who operated the trail closed it off after 150-200 meters (5-10 mins from the ticket booth) due to damage to the trail from the storm. However, what we did see was encouraging. There were so many butterflies that I’m not even sure how to estimate their number. At the very least there were thousands and thousands, if not hundreds of thousands. The air was thick with them, and there was hardly a surface that wasn’t covered in monarchs. Most of the pine trees were completely covered, and were even drooping due to the weight. Now, I’d just like to clarify again that we weren’t able to see the entire trail, but what we did see looked great.**

El Rosario

There weren’t as many butterflies at Chincua, but at the same time there was definitely a lot less damage from the storm, not to mention that none of the trail needed to be blocked off by the people managing the trails. We were able to see a section of the forest (at least several hundred square meters) that was also covered in butterflies, but not as densely as in El Rosario. My dad and I agreed that it looked like there simply aren’t as many butterflies at Chincua storm or no storm.

Sierra Chincua

* In a subsequent communication Don confirmed that this road is now open. He added this note: “Although the Ocampo route to El Rosario was open, we were among the only people we saw there the entire time, besides a couple of a Mexican tourists. It looks like the people who depend on this are probably going to get hit hard economically.”

** It sounds like this is the same area visited by Paul and Phill Justice of Rocamar Tours on the 19th as described in another blog post (“Driving Through Mexico After the Storms“).

Received 26 February from Paul and Phill Justice, Rocamar Tours:

Based on numerous visits each year over the past ten years, our visits to Chincua and Cerro Pelon over the past couple of days have been good at best. The butterflies at Chincua are dispersed over a fairly large area so the area available for viewing by visitors is quite limited resulting in a good showing at best. It continues to be unseasonably cold resulting in not near as many butterflies in flight as we have experienced other years. There is considerable wind damage with trees down throughout area, but no tree damage within the sanctuary itself. There are not many more butterflies dead than we would normally expect to see at this time of year.

We reported on Rosario last week. The condition of the sanctuary was quite dismal with very few butterflies and fewer visitors. It was the worst we had seen it.

We visited Cerro Pelon yesterday. The butterflies were 45 minutes from Macheros on horse-back. There were a fair number of butterflies streaming down the valley and onto the lower trail all the way into the village about mid-morning. The streaming would be about half what we would normally see on the trail. By comparison, last year the last week of February and first week of March, the number of butterflies in the air was spectacular and some of the best showings we have ever seen. In the sanctuary itself there appears to be a good number of butterflies in the trees over an extensive area. The fact that the weather continues to be unseasonably cool results in fewer butterflies in the air, even at the ideal time of day. There may very well be a similar number of butterflies in the sanctuary this year, however most are still on the trees. There are very few dead butterflies on the forest floor and no visible wind or rain damage anywhere in the area. The vigilantes told us that even though there are more open areas with flowers and nectar on the other side of the mountain, it has been far too cold for the butterflies to move over to that area. There are virtually no butterflies on the other side (or the “exit side”) of the mountain.

Received 26 February from Bill Calvert and Bonnie Chase:

We visited two Monarch colonies – Chincua on 23 February and Pelon on 24 February.

Chincua: We arrived late ca. 3:00 PM. We found a small largely inactive group strung out along 100m of drainage leading down from the Mojonera Alta into the Arroyo La Plancha. The clusters were small and high indicating that they had moved there from some other location. These are the type of clusters that appear late in the season. We estimate that at their widest, the area that the butterflies occupied was 50 to 30 meters across. But it was difficult to tell because the ejidotarios did not allow us very close to the colony. Some dead butterflies were scattered about, but not so many where we were. Some of the dead ones were greasy indicating that they had frozen or had been preyed upon; others showed no greasy appearance and had flattened abdomens that felt empty when squeezed. These had likely starved. The low vegetation showed frost damage – curled and browned leaves.

Pelon (or Macheros): At the approach to the community of Macheros we found butterflies streaming down (and up) the mountain. There was considerable flight activity – a behavior that we usually encounter later in the season. After an hour’s horse-back ride up the steep slopes of the Cerro Pelon we arrived (ca. 2:30) at the Pelon colony. Here we found a very densely packed colony also strung out along 80m of canyon leading down from the Gota de Agua. This aggregation was not wide (maybe 30 m), being confined by the steep canyon sides. The forest guards explained that this was the largest of three groups that were spread out along the canyon. The day was considerably warmer than the previous day at Chincua. There was much activity – flying, basking and roosting. Our impression was that there were many more butterflies here than at Chincua. A number of dead were strewn about the forest floor, but nothing like in past seasons after major storms. We detected no frost damage to vegetation at the butterfly colony or its approaches.

25 February Herrada (nr. Valle de Bravo). The following account was created from a phone conversation with Tom Emmel.

This colony measured 0.06 hectares in December – perhaps 20-25 trees. Tom Emmel and Court Whelan visited the site on the afternoon of 24 February.

Hundreds of monarchs were crossing the road leading to Herrada from Valle de Bravo. Police were present and driving speeds were reduced to 15km/hr. The horse ride to the colony took about 50 minutes. The colony was located at the top of a west facing valley. The N slope of valley had three trees whose trunks were covered with monarchs while the S slope contained 4 trees with clusters of monarchs. Lots of monarchs were in the air with many seen streaming down the mountain to the west evidently in search of water. Many were seen taking water at a moist area. There were relatively few dead and only one mating pair was seen. The clusters on the trees were located at heights from 12-15 feet at the bottom to 30-35 feet, with bare trunk and branches above 35 feet. Since a large proportion of the butterflies were in flight, the colony was probably larger than the 7 trees seen – perhaps as many as 10 trees assuming all came back to roost.

The colony was located at N 19 11 15.8; W 99 57 40.4 – at an elevation of 10,452.

24 February. A report by phone from Tom Emmel:

Tom Emmel (Expedition Travel, McGuire Center, U. FL) and his entourage visited Cerro Pelon on Saturday 20 February. Their route to the monarchs took nearly an hour. Tom estimated that the area occupied by monarchs to be roughly 3 hectares (note that a guide told Trecia the area was about 1 hectare). The colony was located at 9,072 feet (N 19.22,46.5, W 100.16,4.2). The colony was nothing short of spectacular and Tom declared it was the best viewing experience he has had in 25 yrs of visiting the monarch colonies. There was little evidence of wind damage at Pelon and in the surrounding area. Tom heard nothing about a second colony. There was no evidence of high mortality at this site.

Tom and his party visited Sierra Chincua on the 21st. The butterflies were located to the east at 10,374 feet (N 19.41,11.6, W 100.17,47.0). The number of occupied trees was only about 10% of the number seen in January. The colony is highly scattered along the east side of Chincua and small clusters and groups of occupied trees were found here and there for over 1.5 km as the group descended the trail. There were no signs of massive mortality but the colony had moved and scattered due to the storms. Wind damage was evident throughout the area. The guides maintained that only 10% of the butterflies had died as a result of the storms. Due to the scattered distribution of the living butterflies, it will be very difficult to accurately assess the mortality at this site.

There is still no clear picture of the condition of the colony at El Rosario.

In case anyone is wondering – it is roughly 22 miles from Chincua to Pelon – about two hours of air-time for a monarch.

23 February. The following is a summary of several reports, including that of Trecia Neal from Monarchs Across Georgia.

Visitors to Chincua are being taken to a colony that is only about 20 mins by horse from the head of the trail. One visitor said she only saw 10 trees with monarch clusters, while a second visitor (last Wednesday) only saw 4-5 trees with monarchs, however, the conditions were cold and rainy so the full extent of the colony may not have been evident. Both were under the impression that the colony they saw was the only one at Chincua.

To give you some perspective there was only one colony at Chincua in December and it measured 0.47 hectares (WWFMX report). The tree density at Chincua is usually given as 350 trees per hectare so the colony would have occupied roughly 160 trees at that time.

The Chincua and Rosario colonies were hit by a severe storm with hail and 40-50 miles/hr winds on 14-15 January that evidently had the effect of spreading out the colonies. (An earlier storm may also have helped to disperse the colonies). On 17 January Tom Emmel (Expedition Travel, McGuire Center, U. FL) estimated that the Chincua colony occupied 1.7 hectares (equivalent to almost 600 trees). So, reports of the relatively small number of trees presently occupied at Chincua is shocking. Lets’ hope there is another colony and that the guides were simply directing visitors to the most accessible site.

Although a long time resident in Zitacuaro, Pablo Span, reported seeing (2 February) more dead monarchs at Cerro Pelon than he had ever seen before, Trecia Neal (Monarchs Across Georgia) reported that as of Friday (19 February) the monarchs at Pelon were doing well.

Quoting Trecia – “The butterflies were about 40 minutes up the trail by horse…back where they usually where down the trail into the trees…not up in the meadow area where they have been for the last two years. They were magnificent! I did notice quite a few dead butterflies here, and noticed that the sex ratio was about 2:1 male to female. There was a lot of flying that day, but it was still cool and the butterflies were still shivering to generate heat. They looked to be in quite good condition. We sat at the end of the trail in a swarm of butterflies for about an hour, and I didn’t notice very many tattered butterflies at all, in fact, many of them seemed to be in pristine condition! The guide that we spoke to said that they estimated the colony to be about 1 hectare in size! He said that there was another large group up a little higher, and that they had been moving down the mountain.”

In December there was a single colony at Pelon that measured 0.53 hectares according to the WWFMexico report prepared by Euardo Rendon and his colleagues. Evidently this colony split, moved and spread out over a larger area. It is not uncommon for colonies to spread out over a broader area as the season progresses.

  1. 3 Responses to “Post-Storm Status of the Monarch Colonies in Mexico”

  2. By Karyl on Mar 9, 2010

    Thank you for all of the updates. They are outstanding.

  3. By Susan on Aug 3, 2010


    Out of the past 3 years that my husband and I have been gardening for birds and butterflies, this year we have 3-4 tmes as many Monarchs as the past 2 years. Out of the past 5 weeks, I don’t think we had more than 3-5 days without seeing between 2-6 of them in our gardens. So, here in Lincoln, Nebraska, we don’t see anything but higher #’s of Monarchs…no change in the # of milkweed plants in our gardens either. Just passing on info 🙂

  4. By bedspreads coverlets on Aug 13, 2010

    I used to see monarch butterflies all the time growing up by now I rarely ever see one, even in the spring and summer I see very few.

    Just shows what human beings are doing to not only to the environment but the wildlife as well 🙁

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