Monday, November 28, 2011

Invasion of the Egret!

Little Egret, Egretta garzetta
Its easy to see the attraction to the Little Egret (Egretta garzetta). Its snowy-white plumage contrasts beautifully with its black, dagger-like bill. Unfortunately the attraction proved to be the undoing of E. garzetta populations in Britain and Ireland. In the breeding season the adult grows two long nape feathers (1). E. garzetta was hunted to extinction in much of norther Europe for these feathers which were used in the production of hats (2). This example of fashion gone crazy resulted in the death of millions of Little Egrets up to the start of the 20th century when a combination of changing fashion tastes and a growing awareness in conservation reduced the hunting of the bird (3).
E. garzetta became an occasional winter visitor in Ireland after this time and up until late 1980's and early 1990s. Large numbers of autumn migrants in 1995-6 lead to a wintering population of about 60 birds. Finally in 1997 a breeding site of 12 birds was established on the River Blackwater on the border between counties Cork and Waterford (4). Breeding sites have increase since then and now Cork has four further established (at Ballannan Wood, Fota Island, Rostellan and the Atlantic Pond) and one possibly established (Carrigaline) sites (5). In these sites, the birds nest in close porximity to the Grey Heron (Ardea cinerea). While the reestablishment of E. garzetta is a welcome development, the speed which with this has occurred is very interesing: from no birds to six breeding sites in just twenty years.

  1. Sterry, 2004. Collins Guide to Irish Wildlife p. 36
  2. Stubbs, 1910. Zoologist 14 pp. 310-311
  3. Bourne, 2003. British Birds 96 pp. 332-339
  4. Smiddy and Duffy, 1997. Irish Birds 6 pp. 55-56
  5. O'Donoghue and Smiddy, 2008. In Practice p. 14

Come Fly With Me

Migrant Hawker, Aeshna mixta
The Migrant Hawker dragonfly (Aeshna mixta) is a relatively new addition to the odonate fauna of Ireland, with the first sighting being reported in 2000 (1). However, this was during the DragonflyIreland survey of dragonflies and damselflies and it may have been present before this. It has the latest emergence of all dragonflies in Ireland, appearing in in the south and south-east of the country in late July and present till late October. Its flight is quite impressive to behold:- hovering around low-lying vegetation, it can quickly shoot high into nearby treetops with ease. Studies of the flight in Aeshna spp. using both tethered animals and model wings have revealed it to be a very complex process (2). It was seen that Aeshna spp. fly by using unsteady aerodynamic mechanisms to generate leading edge vortices or high lift when needed and that the dragonfly controls the flow mainly by changing the angle of attack of the wings. Unsteady aerodynamics refers to the effects on flight that changes in the air flow or in the position or orientation of a body (in this case a wing).
Migrant Hawker, Aeshna mixta
  1. Nelson and Thompson 2004. The Natural History of Ireland's Dragonflies pp. 193-199
  2. Wang and Sun, 2005. The Journal of Experimental Biology 208 pp. 3785-3804

Thursday, November 10, 2011

Sticking with it: Footprints of the Starfish

The most common starfish found in Irish waters, and in the north-east Atlantic as a whole, Asterias rubens can be found in quite deep waters, but is usually found in the intertidal region where it feeds on a variety of molluscs (1). The quantity of prey to be found is quite high here, but so are the challenges posed to A. rubens. These chiefly come from the disruptive action of waves, which can easily wash individuals onto the shore line, which is just what happen to the starfish pictured.
Common Starfish, Asterias rubens
A. rubens overcomes this by the ingenious use of adhesives. The numerous tube feet located on the underside of the animal that are used for locomotion, secrete globular nanostructures forming a meshwork deposited on a thin homogeneous film (2). Two cell types have been identified in the production of this adhesive material:- type 1 cells, which produce the material forming the meshwork, and type 2 cells which are responsible for the release of the material constituting the homogeneous film. These will leave behind a footprint with a reticulate pattern on the substrate. This pattern is due to the arrangement of the adhesive cell secretory pores on the disc surface of the tube feet.

  1. Allen, 1983. Journal of Experimental Marine Biology and Ecology 70 pp. 79-90
  2. Hennebert et al., Journal of Structural Biology 164 (2008) 108–118