A chance meeting and perhaps some insights on the spring migration

Note: the following posting was originally sent by Chip Taylor via Monarch Watch’s Dplex-L email discussion list on 1 May 2000.

Yesterday (Sunday 30 April 2000), while visiting the Baker Wetlands in south Lawrence with David Gibo, I stopped to chat with Lexie Powell, an avid birder who has tagged with Monarch Watch. I asked Lexie if he had seen any monarchs and he replied that he had seen 20-30 the previous day. We were astounded. I had only seen one monarch this year (12 April) and had yet to find eggs even though Steve Case had found eggs on his milkweeds a few miles to the NW of Lawrence.

Naturally, we wanted to know where Lexie had seen these monarchs and he directed us to a hilltop cemetery south of Lone Star Lake (SW of Lawrence). Lexie reported seeing monarchs roosting in the tall pines and junipers at the cemetery. This sounded plausible so we obtained directions and reached the location in mid-morning. Sure enough, the monarchs were there. We managed to collect 4, three males and one female while they visited dandelions for nectar. The monarchs appeared to be moving through the area in mid-day. Photos of each of the monarchs can be viewed at the link below.

One question I have raised in the past concerns the sex ratio of the monarchs that reach the limits of the northward migration for the overwintering generation. I knew that males reached KS but I had never seen enough of the worn and tattered migrants to get a sense of the proportion of males that reach this latitude (39N). During two visits at the cemetery yesterday, we observed 15-20 monarchs. Two of these were females but, judging by their flight behavior and coloration, the majority appeared to be males. Clearly, males are dispersing northward in significant numbers along with females.

Although, one or two of the monarchs appeared to be “bright”, including the last one in the picture series below, all had the appearance of the “brownish orange” that typifies overwintering monarchs. If you look closely at this last monarch, you will see many scratches on the wings typical of older monarchs – even though this specimen appears to be in relatively good condition. It wouldn’t be surprising to see new monarchs from Texas by this date but doesn’t seem likely that any of the monarchs we saw originated in the US this spring. (The images are not quite color true. There is more blue in these images than in real life and the oranges are browner than they appear here).

As we left the site, I spotted some milkweeds growing up through the gravel of the roadbed. We stopped to check for eggs and larvae and were surprised to find large numbers of small larvae in the whorled leaves of the meristem at the top of many plants. One shoot had 8 larvae and another had five. Judging by the size of the larvae, some had just entered the third instar, and, given the recent temperatures and consequent developmental rates for eggs and larvae, most of the oviposition to produce these larvae occurred 9-15 days earlier (15-20 April).

I decided to collect a few of the larvae and quickly discovered that I wasn’t the only collector. Ants and lady bird beetle larvae were busy feeding themselves on the monarch larvae and green aphids on the milkweeds. An ant with a young third instar larva is shown in two of the photos. The ants were beginning to patrol many of the milkweeds and it quickly became clear that if I didn’t harvest the larvae, the ants would do so shortly. It appeared that they had already removed larvae from a number of the plants. I collected approximately 50 larvae.

The lesson in all of this might be the hill. The monarchs appeared to be hilltopping and orienting to the tall pines and junipers in the cemetery. The trees formed an arc to the west in a manner that allowed the butterflies to sun themselves late in the day. In spite of being at the top of the hill, there were several areas that were relatively protected from the sweep of the wind. We visited the site again this evening and there were at least 4 worn monarchs – probably all males – sunning themselves in the trees at heights of 12-35′. David pointed out that hilltopping is consistent with migratory behavior in the fall. In fact, Lexie mentioned that the concentrations of monarchs in these same trees in the fall exceeds anything he has seen elsewhere in eastern KS. Although hilltops appear to be risky sites from the standpoint of storms and high winds, they would have the effect of protecting the monarchs from frosts in the fall as well as the spring. Perhaps when looking for early fall and spring concentrations of monarchs, we should give more consideration to hilltops.

Chip

MALE MONARCH, 56 mm
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FEMALE MONARCH, 52 mm
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MALE MONARCH, 57-58 mm
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MALE MONARCH, 54 mm
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Larvae in whorled leaves of meristem
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An ant with young 3rd instar monarch larva
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All Photos: monarchwatch.org/chip/monarchs