Buffering against food availability? The physical environment has little influence on breeding performance of fairy prions (Pachyptila turtur)

Abstract

The breeding performance of seabirds is constrained by the availability of marine-based prey, which may be influenced by competition with other seabirds, and environmental conditions. Fairy prion (Pachyptila turtur) populations have declined substantially in New Zealand since the introduction of mammalian predators; remaining small populations provide an opportunity to examine the effect of environmental factors on reproductive success in the absence of competition. Using 11 years of nest monitoring data and eight years of chick measurements we investigated (i) the link between physical environmental factors, breeding success rates and chick fledging size, and (ii) the relationship between chick fledging size and likelihood of natal-colony recapture. Despite annual variations in the Southern Oscillation Index (SOI) and sea surface temperatures (SST), breeding success and chick fledging weights remained similar throughout the entire period, possibly due to the use of behavioural buffering mechanisms by parents. Fledgling wing lengths differed among years, and were predicted by early winter and early spring values of the SOI and late spring and summer SSTs. In years of high SOI and high SST, fairy prions fledged with longer wings, possibly due to increased availability of the euphausiid Nyctiphanes australis, their main prey. River flows and rainfall were unrelated to breeding success or chick measurements: the influence of freshwater on the marine system at this locality acts at smaller timescales than those studied here. Using the 2004 and 2005 cohorts, there was no link between fledging size and likelihood of recapture, except for the 2005 cohort which had unusually low 6-year recapture rates, and shorter-than-average wing lengths. A combination of low sea temperatures and an El Niño event in 2005 may have led to a reduction in euphausiid availability, ultimately affecting post-fledging survival.

Temporal and spatial differences in the post-breeding behaviour of a ubiquitous Southern Hemisphere seabird, the common diving petrel

“…In southeastern Australia and New Zealand, the locally abundant coastal krill Nyctiphanes australis [ 82 ] is a key food source for CDP [ 34 ] (C. M. Miskelly 2019, personal observation). However, this euphausiid undergoes extreme inter-annual variations in biomass and distribution, considerably affecting the reproductive success of various fish [ 82 ] and seabird species [ 84 , 85 ]. Populations spending a long period near the colony before the reproductive season are more likely to follow local environmental cues to adapt their phenology [ 83 ], which may explain the significant delay in the breeding period observed between the years in the present study at Kanowna Island [ 78 ].…”

Impact of extreme environmental conditions: Foraging behaviour and trophic ecology responses of a diving seabird, the common diving petrel

“…As a key zooplankton species (Ritz & Hosie 1982), variability in abundance of coastal krill has been observed to influence the foraging behaviour and demographic parameters of various marine predators (Mills et al 2008, Manno et al 2014. For example, in New Zealand, delayed breeding period, longer foraging trips and low breeding success of the zooplanktivorous red-billed gull (Larus novaehollandiae scopulinus) were linked to the absence of coastal krill in years of positive sea temperature anomaly (Mills et al 2008).…”

Year-round at-sea movements of fairy prions from southeastern Australia

“…However, in contrast with the sympatric common diving petrels, fairy prions appeared to buffer the variations in environmental conditions better, owing to their higher flight capacity and the production of stomach oil [ 33 , 66 ]. Indeed, despite being smaller than common diving petrels, the lower wing load of fairy prions enables them to reach more distant foraging areas [ 12 ].…”

“…This is particularly concerning as the frequency and intensity of such extreme events are predicted to increase in the near future [ 28 ]. In addition, although recent studies showed that fairy prions are able to maintain a relatively good breeding success even during poor years [ 33 , 66 ], the long-term consequences of marine heatwaves on juveniles' and adults’ survival remain totally unknown.…”