Editing Little penguin (section)

===Double brooding===
If penguins produce a second clutch of eggs in a season once the first chicks have fledged, this is known as double brooding.<ref name="P Agnew">(Agnew, P., Houston, D., Lalas, C. et al. Variation in reproductive performance of Little Penguins (Eudyptula minor) attributable to double brooding. J Ornithol 155, 101–109 (2014).)</ref> Thus far this behaviour has only been observed in the ''Eudyptula novaehollandiae'', the lineage of little blue penguins which inhabit Australian and Otago regions. There is no evidence to suggest this is an established behaviour within ''Eudyptula minor'', however double broods are occasionally noticed among the colonies in the Kaikoura coastline.<ref>(Rowe, L. K., Weir, J. S., & Judkins, A. G. (2020). Breeding of little penguins (Eudyptula minor), including multiple brooding, at South Bay, Kaikōura, New Zealand, 2006–2017. Notornis, 67(2), 451-458.)</ref>  It is as yet unclear whether this means double brooding is a genetically mediated behaviour. A study carried out on Oamaru penguin colony found double broods to increase breeding success by up to 75% per season.<ref name="P Agnew"/> Double brooding is more likely to occur in individuals who lay their first clutch, prior to mid-September.<ref name="Mattern"/> While there is some interannual variability, the most common period for little penguins to lay their first clutch is in spring, mid-September is considered early and gives individuals time left in the season to lay a second clutch of eggs after the first have fledged.<ref>(Chambers, L. E. (2004). Delayed breeding in Little Penguins–evidence of climate change. Australian Meteorological Magazine, 53(1), 13-19.)</ref>

The onset of double brooding can be strongly influenced by sea surface temperature, age and food availability.<ref>(Grosser, S., Burridge, C. P., Peucker, A. J., & Waters, J. M. (2015). Coalescent Modelling Suggests Recent Secondary-Contact of Cryptic Penguin Species. PloS one, 10(12), e0144966.)</ref> Warmer sea surface temperature in summer and autumn correlated with earlier laying of first clutch of eggs increasing the chances of double brooding.<ref 
name="P Agnew"/>  In contrast, in New Zealand it was observed that during the La Niña phase of the [[El Niño Southern Oscillation]] when colder temperature water was brought to the surface, there was a delay in the onset of breeding for ''Eudyptula novaehollandiae'', thus resulting in a lower incidence of double brooding in the Otago colonies.<ref>(Cullen, J. M., Chambers, L. E., Coutin, P. C., & Dann, P. (2009). Predicting onset and success of breeding in little penguins Eudyptula minor from ocean temperatures. Marine Ecology Progress Series, 378, 269–278.).</ref> Age is also believed to be a factor affecting double brooding because the pairs successfully able to double brood were most commonly strategic in reclaiming successful nests and pair-bonds. Little penguins show a high nest fidelity, and the ability to reclaim success early suggests it is likely that successful double brooding is a behaviour that improves with age. Another influencing factor is the availability of food, for larger colonies such as the Philip Islands, competition for food can increase significantly during the breeding season, particularly if there is variability in the amount of prey available.<ref name="Mattern"/> If this competition results in aggression between adults, this can also influence ability to successfully raise chicks, and successfully breed in the next season.