Wednesday, 24 June 2015

The patrolling Red Admiral

Since the beginning of June, Red Admirals have been well established, having returned from the Mediterranean in their one way spring migration. Females should be mating and looking for sunny nettle patches in which to lay their eggs. Males should be looking for receptive females to mate with. They will produce one or more broods in the summer. As temperatures drop in the autumn, butterflies will prepared themselves for the autumn migration and then they become very apparent in gardens, where they feed on buddleia and other nectar rich flowers. Male and female have the same wing colour pattern. If you have a good view of the abdomen when the butterfly is resting with its wings open,  a swollen abdomen will allow you to identify a female, but otherwise it might be easier to tell them apart by their behaviour in early summer.
  Last week, in the afternoon, I have flushed a Red Admiral from the same sunny spot on a grassy area amongst trees, where they were sitting day after day, exactly where I often found them last year. This afternoon was unusually warm and, as I left work, a Red Admiral sat on a low hedge on a wooded glade teeming with nettles in our university campus (above). It would sit and then fly up patrolling around the trees and chasing passing bumblebees in a similar way a Speckled Wood male would do, and then return to the same perch. I had never noticed this behaviour in the Red Admiral, but it appears that I had observed a male, and that red Admiral males actually defend territories. It might seem hard to believe that beautiful, fluttery butterflies actually engage in any kind of aggressive interaction. Indeed, butterflies have no offensive weapons other than their wings, and, butterfly contests, even when they are defending a territory are often perceived as chases instead of aggressive interactions. However, there is now abundant research showing territorial behaviour in a number of butterfly species. The important point is not the presence of an actual fight but the outcome: as a result of the behaviour the owner remains in the territory and the intruder flies away.    Royce Bitzer and Kenneth Shaw carried out research on the territorial behaviour of the Red Admiral on the Iowa University campus. They captured and marked individual Red Admirals with different spots of paint and observed their behaviour once released. They found that Red Admirals spend the morning feeding, but each evening males establish temporary territories for a couple of hours before roosting. Males spent most of their time perched, but occasionally patrolled their territory boundaries. They were not seen feeding. Birds or other butterfly species were chased in a linear way, but male intruders are chased upwards in a spiral. In Red Admiral chases, the owner often retains ownership and the intruder flies away. Good territories are likely to be an area containing resting spots from where passing females can be easily detected, usually with linear features (e.g. a pavement or a few trees in a line). The maintenance of these temporary territories could allow better access to receptive females moving into their roost, as mating is thought to happen in the roosting sites in trees.
A particularly bright red and intact individual, maybe the result of a first local brood?
Two days later a much more faded individual with tattered wings, on the same favoured spot on the grass.

More information
Red Admiral and Painted Lady Research Site. Here.

Bitzer, R. J., & Shaw, K. C. (1979). Territorial Behavior of the Red Admiral, Vanessa atalanta (L.)(Lepidoptera: Nymphalidae). Journal of Research on the Lepidoptera, 18(1), 36-49. here.

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