Migrant hawkers scramble competition

I'm used to watching migrant hawkers foraging over gardens, leafy streets and sheltered woodland rides, some times in groups. They are immature individuals, gathering energy away from water. Migrant Hawkers, unlike other hawkers, mature slowly, and will move to suitable breeding sites after their long immature period. During this past week I've watched them in their breeding sites in lakes and drains, where mating and egg-laying takes place.

A mature male rests briefly between bouts of searching (Pickering Park, 27th August) 

Males at the breeding site 
At one of my local parks (Pickering Park) last week, dozens of Migrant Hawkers sat or patrolled alongside marginal vegetation around the lake. The males, now fully mature and showing their bright blue spots and eyes and side yellow-green stripes often hovered in a spot, or explored the vegetation, flying well into it, searching for females.

A typical hovering male in a clearing at the marginal vegetation (Pickering Park, 27th August), offering them good views.

Mating
I saw no females, until one was captured by a male: no preliminary or courtship, the male just tackled her and positioned himself to grab her by the head. The female is then able to curve her abdomen and mate, retrieving sperm from the male's secondary genitalia at the base of the abdomen, forming the 'wheel position'. They may fly in wheel position very fast, zigzagging alongside the marginal vegetation edge or briefly rising into the air, before settling on vegetation (above).

Ovipositing female (Foredyke Stream, 1st September)

The moment when the male passes by, and sees the female.

The pair, mating.

Oviposition
A couple of days ago I watched a patrolling male on a ditch doing its usual patrolling routine, rising to inspect any passing individual, even paying attention - briefly rising - to birds flying over. A mated female arrived, unnoticed, and started laying eggs on live leaves well above the water line, I'd say over one metre over the water. She checked leaves and unsheathing her ovipositor, started laying into them (the eggs will overwinter inside the plant leaves, where they are protected from predation). After a couple of minutes, the male noticed her, tackled her and mating ensued. This time the pair settled briefly on plants, which allowed me to take a shot (above). Mating in Migrant Hawkers is longer than in other territorial relatives.

Two males resting near each other (Pickering Park, 27th August)

Nonterritorial males
This species is notoriously non-aggressive, even at the breeding sites. Males will even rest within view from each other (above). A patrolling male will swiftly rise to check a passing one, but the interaction is suggestive of them 'checking' that they are not a female, and letting the other individual go their way if it's a male. There is no defended territory, just males congregating on suitable ovipositing sites and searching for females, a type of mating tactic called 'scramble competition'. This appears to be the reason behind the long copulation. A territorial male mating for a long time may lose the territory to an invader, or miss extra mating opportunities. A nonterritorial male has less to lose, and therefore makes sure that he fertilises as many as possible of the females' eggs, possibly by taking time to remove any previous sperm before transferring his transfer. These patterns have been shown to stand when the copulation duration of territorial and nonterritorial drogonfly species were compared, but I haven't found specific data on the Migrant Hawker. To illustrate the pattern, the Emperor, a territorial species, copulates for an average of 10 min, while the Common Hawker, a non-territorial one, copulates for an average of 67 min. Of course, this lengthy copulation is not necessarily to the benefit of the female, who may be already mated, as the female already laying eggs, and therefore this sets the stage for the evolution of female counter-tactics, such as visiting the water as little as possible and avoiding males if they can, something I have covered before at Bugblog.

More information
Córdoba-Aguilar, A., Serrano-Meneses, M. A. and Cordero-Rivera, A. Copulation Duration in Nonterritorial Odonate Species Lasts Longer than in Territorial Species. Ann. Entomol. Soc. Am. 102, 694–701 (2009).

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 studied 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.

More on Fork-Tailed Flower Bees

I had a super A. furcata watching day in my local wildlife garden today. In a beautiful large patch of flowering Hedge Woundwort (Stachys sylvatica), in the shade, a male (below) kept patrolling, checking every flowering spear visually and darting between them, stopping to feed occasionally.

Two females collected nectar and pollen, at times both together in the same spear. The male came across and pounced a couple of times on a female, but I saw no copulation. Males seem to have a similar patrolling behaviour around favoured flowers as A. plumipes. In my garden it patrols different flowers around it (Iris, Digitalis lutea and D. purpurea). But last year I planted their local native favourite plant, S. sylvatica in a shady corner. Although it is still small, it is now flowering. Something interesting is that these bees do not mind shade or cloudy weather, they will be out and about like bumblebees whatever the weather, so they don't tend to overlap with sun-loving Anthidium manicatum - which has a similar flower choice than them and males aggressively defend territories - so much when they forage. I wonder if they are able to thermoregulate in a similar way than their relative A. plumipes and this allows them to exploit a different niche to other summer bees.

An Anthophora furcata female with legs full of pollen foraging in Stachys sylvatica.