Adelies act like optimal foragers as long as feeding-trips are less than 2 days, the adults did not loose condition while foraging and the chicks thrived. If the trips were longer than 2 days the adults need to metabolise some of their food load (destined to be feed to their chicks) for their own survival.
- Adults balanced self-maintenance against investment in off-spring
- Trip times and meal sizes differ between sexes, but are closely related to parent mass at the start of chick feeding
- Foraging trip duration is related directly to distance from the colony to the nearest pack ice (2 = 0.2034 ± 0.053, P = 0.002)
- Trips are longer and food loads smaller in seasons of heavier ice cover
- Foraging trip distance was greatest and tended to increase as the season progressed at Cape Crozier, the largest colony, but not at the smaller colonies, Cape Bird and Cape Royds.
|Satellite tracking data shows minimal foraging range over-lap between the small colonies (red and yellow circles) and the largest colony (green circles).
|As chicks grow their food demands are greater and parents have to work harder (longer foraging trips) to feed their chicks, especially at Cape Crozier where competition for food is greater.
|Dive depth also increase over time at Cape Crozier.
For more information:
Ainley, D.G., Ribic, C.A., Ballard, G., Heath, S., Gaffney, I., Karl, B.J., Barton, K.J., Wilson, P.R. and Webb, S. (2004). Geographic structure of Adelie penguin populations: overlap in colony-specific foraging areas. Ecological Monographs 74(1): 159–178.
Ainley DG, Wilson PR, Barton KJ, Ballard G, Nur N, Karl B 1998. Diet and foraging effort of Adélie penguins in relation to pack-ice conditions in the southern Ross Sea. Polar Biology 20: 311–319.
Ballance LT, Ainley DG, Ballard G, Barton K 2009. An energetic correlate between colony size and foraging effort in seabirds, an example of the Adelie penguin Pygoscelis adeliae. Journal of Avian Biol. 40: 279–288.
Lescroel A ,Ballard G, Toniolo V, Barton KJ, Wilson PR, Lyver PO'B, Ainley DG. 2010.Working less to gain more: when breeding quality relates to foraging efficiency. Ecology 91(7): 2044–2055.