Massey Documents by Type

Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294

Browse

Has files: YesSubject: search.filters.subject.Bar-tailed godwit

Search Results

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    The roles of morphology, individuality and arrival from migration in the foraging ecology of bar-tailed godwits at the Manawatū River estuary : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Zoology at Massey University, Manawatū, New Zealand
    (Massey University, 2018) Ross, Tobias Alexander
    Bar-tailed Godwits (Limosa lapponica baueri) are a hugely size-variable shorebird exhibiting reverse sexual dimorphism as well as substantial variation within the sexes. This variation is especially pronounced in bill lengths, and differences in bill size could result in dietary differences between individuals. I studied the foraging ecology of individually-marked godwits at the Manawatū River Estuary in New Zealand, a small site amenable to making repeated observations of birds by videography. Specifically, I investigated the effects of bill size variation on intake rates and diet composition of godwits and tested for individual specialisation. Birds were found to use prey-specific foraging modes, the effect of which far outstripped that of any morphological or environmental factor. I found that shorter-billed birds (males) had slightly higher and less variable intake rates than their longer-billed (female) counterparts. The shorter-billed birds focused their efforts on catching small surface prey such as Potamopyrgus, to the extent where around half of the males specialised on these small snails. In comparison, longer-billed birds ate a more diverse array of prey items, notably consuming more worms which were buried deeply in the sediment. In addition to some birds specialising on certain prey, other prey were taken preferentially by only certain individuals across the size spectrum. This suggests that the diets of godwits are not only influenced by morphology but also by individual preferences of the birds themselves. I also tested for a carry-over effect of prolonged flight on foraging performance of godwits. The 8–10-day post-breeding migratory flight of godwits direct from Alaska to New Zealand is the longest known endurance flight of any land-bird. This flight has many expected physiological impacts, including a reduction in digestive tract mass that could lead to lower functionality of the digestive tract and therefore limit intake rates after arrival. By monitoring the daily occurrence of marked birds I determined when birds arrived on migration, and tested whether intake rates and diet choice changed in the fortnight after birds arrived. I found that intake rates were slightly higher and less variable with time since arrival. Furthermore, there was an increase in the consumption of the hard-shelled mud snail Amphibola crenata with time, suggesting a recovery of gizzard mass. Given the scale of the migration, however, these effects were surprisingly small and imply that diet choice and energy intake are affected only slightly by a physiological carry-over effect from migration.
  • Thumbnail Image
    Item
    The Northward migration stopover ecology of Bar-tailed Godwits and Great Knots in the Yalu Jiang Estuary, National Nature Reserve, China : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology, Massey University, Palmerston North, New Zealand
    (Massey University, 2015) Choi, Chi-Yeung
    Stopover ecology is the scientific study of the behaviour of migrants, the interrelationships among migrants, and between migrants and their environment, at stopping sites. Many shorebird species are long-distance migrants and require high quality stopping sites to rest and refuel during migration. The suitability of a stopping site depends mostly on food availability, level of competition, and predation or disturbance pressure. Events at stopover may not only affect migration performance, but also the subsequent reproduction or survival, and therefore become the limiting factor for the population sizes of migrants. The stopping sites in the Yellow Sea along the East Asian-Australasian Flyway are used extensively by long-distance migratory shorebirds along the flyway, but very little is known about the stopover ecology of these birds. Moreover, the stopping sites within the Yellow Sea region are under serious threats; some of them are being lost before their importance to shorebirds is fully understood. In this thesis, my aim was to study the stopover ecology of Bar-tailed Godwits Limosa lapponica and Great Knots Calidris tenuirostris at an important stopping site in the northern Yellow Sea, the Yalu Jiang coastal wetland, during northward migration between 2010 and 2012. I estimated the number of these shorebirds transiting and their passage dates using repeated counts incorporated with Thompson’s modelling approach. I described the type, abundance and characteristics of their benthos resources by benthos sampling. I investigated their dietary compositions, foraging patterns and mechanisms of coexistence by behaviour scans, focal bird observations and faecal dropping analysis. Finally, I studied their predation impact on their main bivalve prey, Potamocorbula laevis, using exclosures. My results indicated that at least 42% of the East Asian-Australasian Flyway’s northward migrating L. l. baueri godwits, 19% of L. l. menzbieri godwits, and 22% of the Great Knots used Yalu Jiang coastal wetland, thereby indicating the importance of the study area to these species. Polychaetes and bivalves numerically dominated the benthic communities, while one bivalve species, P. laevis, constituted more than three quarters of total macrobenthic biomass during the study period. Great Knots, Red Knots Calidris canutus and Far Eastern Oystercatchers Haematopus ostralegus osculans selected mostly the bivalve P. laevis while Bar-tailed Godwits had a broader diet and selected mostly polychaetes, even though most of their intake was of P. laevis. Moreover, the size of P. laevis preferred by godwits and Great Knots overlapped. Their coexistence seems to be enabled by high resource availability rather than niche separation. The different dietary selections between godwits and knots possibly led to different foraging patterns on the tidal flats. There was clear behavioural evidence that a digestive bottleneck existed in the bivalve-feeding shorebirds. Such digestive constraints of hard-shelled prey, decreased prey quality (amount of energy per dry mass of shell taken), and increased handling and searching time were potential reasons behind a decline in total biomass intake rate in godwits and Great Knots from 2011 to 2012, despite similar numerical and biomass density of their main prey in both years. Finally, there was evidence that predation by shorebirds had a significant impact on the number of P. laevis in one of the years studied. My thesis showed the importance of Yalu Jiang coastal wetland to Bar-tailed Godwits and Great Knots during northward migration. These two species competed for the same bivalve prey and their coexistence in the years of study was enhanced by ample food resources rather than niche differentiation. The lack of young P. laevis recruitment in the final year of study and the significant predation impact detected indicated a potential decline in food resources after my study. Long-term monitoring will reveal how these species respond to the changes in prey availability. My study provided important scientific information on the numbers of birds using Yalu Jiang coastal wetland, their prey resource availability, their dietary compositions, and behaviours that are crucial for their conservation management in the reserve and potentially in other stopping sites in the Yellow Sea.
  • Thumbnail Image
    Item
    Tactile senses and foraging in birds, with emphasis on kiwi : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Manawatu, New Zealand
    (Massey University, 2010) Cunningham, Susan Jane
    Probe-foraging birds must often rely on senses other than vision for prey-detection. One such sense is ‘remote touch’: the detection of vibration and pressure cues from prey within the substrate. Remote touch is mediated by the ‘scolopacid-type bill-tip organ’, which consists of a honeycomb of sensory pits in the bill-tip, containing clusters of mechanoreceptors. This organ was originally described in the neognathous shorebird family Scolopacidae, but was recently also discovered in paleognathous kiwi (Apterygidae): an example of convergent/parallel evolution. My aim was to discover how widespread this organ is among birds, compare its anatomy and function in foraging between kiwi and other probe-foraging birds and elucidate in detail the foraging behaviours and senses used by free-living kiwi. Within the thesis I compare the bill-tip organs of kiwi and shorebirds using material from the brown kiwi (Apterygidae: Apteryx mantelli) and bar-tailed godwit (Scolopacidae: Limosa lapponica). I provide the first description of the organ in a third family of birds, the ibises (Threskiornithidae), and give evidence that it may exist in simplified form in a fourth family, Rallidae. The Scolopacidae, Apterygidae, Threskiornithidae and Rallidae are widely separated on the avian phylogenetic tree. This suggests that the evolution of the scolopacid-type bill-tip organ and associated sense is favoured by a probe-foraging lifestyle. Foraging trials confirm the bill-tip organs of brown kiwi and Madagascar crested ibises (Lophotibis cristata urschi) are functional for remote touch. The ibises rely solely on remote touch to find buried prey, whereas brown kiwi use the sense in conjunction with olfaction. Free-living brown kiwi display no obviously visually-guided behaviours, instead using hearing (head-lifting in response to noises audible to the observer), olfaction (odour sensing behaviour, ‘sniffing,’ in the direction of these sounds) and touch. Kiwi tap ahead with their bill-tip when walking and move their facial bristles forward when foraging, forming a ‘net’ on the ground. The bristle follicles in kiwi (and some other insectivorous bird species) are innervated with Herbst corpuscles, suggesting tactile function. Female kiwi probe on average 30% deeper than males and juveniles, but there are no other differences in foraging behaviour between the sexes.
  • Thumbnail Image
    Item
    Extreme migration and the annual cycle : individual strategies in New Zealand Bar-tailed Godwits : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Palmerston North, New Zealand
    (Massey University, 2011) Conklin, Jesse Ray
    Long-distance migration places severe constraints on the annual cycles of birds, as they balance the energetic and scheduling requirements of breeding, moult, pre-migratory fuelling, and the journey itself. The most extreme migrations, traversing vast, inhospitable areas of the globe in protracted non-stop flights, may push birds to the limits of their capabilities, and would be expected to tolerate little variation in performance. Despite this, Bar-tailed Godwits Limosa lapponia baueri, which are among the world’s greatest endurance migrants, embark on northward migration from New Zealand across a month-long period, and individuals are quite faithful to their particular schedules. Godwits are highly sexually dimorphic in plumage and body size, and there is additionally substantial individual variation within each sex in both traits. These patterns demonstrate a surprising diversity of strategies within a system that should contain little room for error. In this thesis, I sought to identify the roots and consequences of both persistent and ephemeral individual differences in migration and moult of New Zealand Bar-tailed Godwits, and to identify constraints and potential bottlenecks in their annual cycle. To do this, I combined a fine-resolution multi-year focus on individuals and an entire annual-cycle perspective, both of which have generally been impossible in studies of long-distance migratory birds. At a single non-breeding site, I closely monitored moult and migration of individual Bar-tailed Godwits for three non-breeding seasons, and linked these with events outside of New Zealand by tracking a subset of the same individuals on their complete migrations to Alaska breeding grounds and back. I supplemented this by travelling to Alaska myself and describing how godwits are distributed by size and plumage across their vast breeding range. I found that most of the variation among individual Bar-tailed Godwits was linked to where they nested in Alaska: within each sex, northerly breeders were smaller, had more extensive breeding plumage, and migrated later on both northbound and southbound migrations. The differences in migration timing can be explained by variation in when tundra breeding sites become snow-free and available across a latitudinal gradient, but reasons for geographic differences in plumage and size are less clear. Variation in breeding plumage was associated with different strategies for scheduling moult, both in New Zealand and during northbound migratory stopover in the Yellow Sea. Individual godwits were extraordinarily consistent between years in their timing of departure from New Zealand, and most ‘off-schedule’ departures were attributable to birds avoiding unfavourable winds for migration. Surprisingly, timing of arrival in New Zealand after the longest recorded non-stop flight did not appear to influence a godwit’s ability to prepare for its next migration, as timing of subsequent migratory departure and extent of breeding plumage on departure were both unaffected and very consistent. Across the entire year, scheduling of events became more precisely timed as the breeding season approached, but movements were generally much more tightly scheduled than moults. These findings show that Bar-tailed Godwits adopt and enact an array of individualised strategies within an apparently constrained system. The inter-relationships among events in different parts of the globe show that an individual-based, full annual-cycle perspective is required to understand patterns in any particular season. The consistent manner in which godwits conduct their annual routines, while still demonstrating flexibility to address unforeseen circumstances, challenges us to reconsider the view of extreme long-distance migrants as organisms operating at the limits of their capabilities.