Ecological segregation of two superabundant, morphologically similar, sister seabird taxa breeding in sympatry

Abstract

Prions Pachyptila are the most abundant seabirds in the Southern Ocean and comprise two main groups: those with and without bill lamellae to filter zooplankton. With few exceptions, each breeding location supports at most one species from each of these groups. However, Gough Island supports two morphologically very similar, filter-feeding species: broad-billed P. vittata and MacGillivray's prions P. macgillivrayi. To understand how these two species co-occur in sympatry, we compared the foraging ranges, habitat selectivity, trophic segregation and moult schedules of these species using combined geolocation-immersion loggers. After breeding, both species showed a well-defined westward migration prior to moulting. Moult lasted 11 to 19 weeks and was significantly longer in MacGillivray's than broad-billed prions. Moulting birds occurred in specific areas within the Argentine Basin, with little overlap between the two species. Habitat analysis revealed species-specific preferences, in particular sea surface temperature. Activity patterns also differed; MacGillivray's prions spent more time in flight, which indicates a more active foraging strategy, relying less on filter feeding. Stable isotope ratios (δ 15 N) in flight feathers were greater in MacGillivray's prion, which is consistent with its less specialized bill morphology resulting in feeding at a higher trophic level. Inter-specific spatial segregation was observed for most of the tracking period, in large part because broad-billed prions breed roughly 3 months earlier than MacGillivray's prions. At Tristan da Cunha, 250 km farther north, where only broad-billed prions breed, they departed, moulted and returned significantly later (15-17 days) than conspecifics from Gough Island, providing evidence for character displacement in sympatry with MacGillivray's prion.

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

“…In the present study, a substantial increase in the proportion of time spent on water 30–40 days after migration departure was found in all sites and years. Such a pronounced pattern of activity has been associated with the renewal of flight feathers in several small procellariiform species [ 29 , 50 ]. Migratory diving birds, such as some species of alcids and diving petrels, are known to undergo a rapid wing moult in early post-breeding period, temporary affecting their flight ability [ 46 ].…”

“…Owing to the high-energy cost of carrying telemetry devices, there is a trade-off between the size of animal-borne transmitters and their deployment duration such that their application in seabirds has been constrained to species with larger body size and/or for a relative short period [ 24 ]. Daylight sensing geolocation provides a lightweight alternative for long-term deployments (geolocation sensing data loggers, GLS) and is increasingly being used to investigate the at-sea distribution and activity of small procellariiform species during the breeding [ 25 , 26 ] and non-breeding periods [ 27 – 29 ].…”

Contrasting impacts of environmental variability on the breeding biology of two sympatric small procellariiform seabirds in south-eastern Australia

“…Similarly, low food availability during the non-breeding period can induce low breeding performances through carry-over effects [75]. This period is critical for both study species, as adults need to restore their body reserves and, more importantly, undertake the energetically costly renewal of their plumage [37,76]. In the post-breeding area of CDP in the Southern Ocean, zooplanktonic communities can be affected by warmer sea surface temperatures [77] impacting the body condition and survival of planktivorous seabird species [78].…”

Foraging behaviour and habitat-use drives niche segregation in sibling seabird species

“…We tested the null hypothesis of no spatial segregation by permuting the individual track labels (sex or species, as appropriate) 1000 times and calculating overlap for each permutation (e.g. [15]). Since interannual variation in resource availability and environmental conditions may influence foraging behaviour, we constrained the permutations by year.…”

“…Niche segregation among related species, and between the sexes, has often been found in seabirds (e.g. [8,[15][16][17][18][19][20]) and two complementary tools have been particularly useful in providing this information. Tracking data allow us to quantify the space use of seabirds and, in conjunction with remote sensing data, allow us to quantify the environmental conditions-and thus the habitat-used by them [21].…”