Habitat use throughout migration : linking individual consistency, prior breeding success and future breeding potential

1. Habitat use can influence individual performance in a wide range of animals, either immediately or through carry-over effects in subsequent seasons. Given that many animal species also show consistent individual differences in reproductive success, it seems plausible that individuals may have consistent patterns of habitat use representing individual specializations, with concomitant fitness consequences.

2. Stable-carbon isotope ratios from a range of tissues were used to discern individual consistency in habitat use along a terrestrial–aquatic gradient in a long-distance migrant, the Bewick’s swan (Cygnus columbianus bewickii). These individual specialisations represented <15% of the isotopic breadth of the population for the majority of individuals and were seen to persist throughout autumn migration and overwintering until aquatic habitats were no longer available.

3. Individual foraging specialisations were then used to demonstrate two consecutive carry-over effects associated with macroscale habitat segregation: consequences of breeding season processes for autumn habitat use; and consequences of autumn habitat use for future reproductive success. Adults that were successful breeders in the year of capture used terrestrial habitats significantly more than adults that were not successful, revealing a substantial cost of reproduction and extended parental care. Use of aquatic habitats during autumn was, however, associated with increased body condition prior to spring migration; and increased subsequent breeding success in adults that had been unsuccessful the year before. Yet adults that were successful breeders in the year of capture remained the most likely to be successful the following year, despite their use of terrestrial habitats.

4. Our results uniquely demonstrate not only individual foraging specializations throughout the migration period, but also that processes during breeding and autumn migration, mediated by individual consistency, may play a fundamental role in the population dynamics of long-distance migrants. These findings, therefore, highlight the importance of long-term consistency to our understanding of habitat function, interindividual differences in fitness, population dynamics and the evolution of migratory strategies.

Establishment and development of a seabird colony : long-term trends in phenology, breeding success, recruitment, breeding density and demography

Few studies document long-term colony-level metrics from colony establishment to maturity (equilibrium) and few test predictions of general models of colony development. We describe long-term trends in a colony of Australasian Gannets (Morus serrator) which has been monitored from an early stage in its development. The colony at Pope’s Eye, within Port Phillip Bay, Victoria, Australia was established in 1984 on an artificial structure and the first nest count (25 nests) was conducted in the same year. The colony was then studied for 15 of 19 years between 1988 and 2006–2007. During the study, 2,516 eggs were recorded, resulting in 1,694 chicks hatching (67 % of eggs), of which 1,310 (77 % of those hatched) fledged. At least 184 (14 %) of fledged offspring returned to Pope’s Eye as breeding adults. Since establishment, the number and density of nests increased (number of nests increased 8.8 % annually), with density increasing at varying rates in different areas of the colony. Early recruitment involved birds from a nearby colony, but within 5 years post establishment the first natal recruits were breeding at Pope’s Eye and thereafter natal recruitment was the main source of new breeding adults (totalling 81.4 % of all recruits). Age of recruitment varied throughout the study, though not systematically, and there was no difference between the sexes. The pattern of rapid initial growth is typical of patterns reported for other seabird colonies. However, as the colony (and birds within it) aged, there was no increase in breeding success and egg laying did not become earlier, as was expected from general models of colony development.

Factors affecting breeding success in Peregrine Falcons (Falco peregrinus macropus) across Victoria 1991 - 2012

Peregrine Falcon’s lifetime reproductive outputs are influenced more by the quality of the nest site than by the environmental landscape in which they live. The installation of a nest boxes significantly improves breeding outcomes. Uniquely, Victorian Peregrines use novel (non-cliff) nest sites and disperse considerably shorter distances to adopt these sites.

Loss of periodicity in breeding success of waders links to changes in lemming cycles in Arctic ecosystems

Lemming population cycles in the Arctic have an important impact on the Arctic food web, indirectly also affecting breeding success in Arctic-nesting birds through shared predators. Over the last two decades lemming cycles have changed in amplitude and even disappeared in parts of the Arctic. To examine the large scale effect of these recent changes we re-analysed published data from the East Atlantic Flyway (EAF), where a relationship between lemming cycles and wader breeding success was earlier found, and new data on breeding success of waders in the East Asian-Australasian Flyway (EAAF). We found that 1) any long-term periodicities in wader breeding success existed only until the year 2000 in the EAAF and until the 1980s in the EAF; 2) studying these patterns at a smaller spatial scale, where the Siberian-Alaskan breeding grounds were divided into five geographical units largely based on landscape features, breeding success of waders from the EAAF was not correlated to an index of predation pressure, but positively correlated to Arctic summer temperatures in some species. We argue that fading out of lemming cycles in some parts of the Arctic is responsible for faltering periodicity in wader breeding success along both flyways. These changed conditions have not yet resulted in any marked changing trends in breeding success across years, and declining numbers of waders along the EAAF are therefore more likely a result of changing conditions at stop-over and wintering sites.

Effects of sea temperature and stratification changes on seabird breeding success

As apex predators in marine ecosystems, seabirds may primarily experience climate change impacts indirectly, via changes to their food webs. Observed seabird population declines have been linked to climate-driven oceanographic and food web changes. However, relationships have often been derived from relatively few colonies and consider only sea surface temperature (SST), so important drivers, and spatial variation in drivers, could remain undetected. Further, ex - plicit climate change projections have rarely been made, so longer-term risks remain unclear. Here, we use tracking data to estimate foraging areas for 11 black-legged kittiwake Rissa tridac - ty la colonies in the UK and Ireland, thus reducing reliance on single colonies and allowing calculation of colony-specific oceanographic conditions. We use mixed models to consider how SST, the potential energy anomaly (indicating density stratification strength) and the timing of seasonal stratification influence kittiwake productivity. Across all colonies, higher breeding success was associated with weaker stratification before breeding and lower SSTs during the breeding season. Eight colonies with sufficient data were modelled individually: higher productivity was associated with later stratification at 3 colonies, weaker stratification at 2, and lower SSTs at one, whilst 2 colonies showed no significant relationships. Hence, key drivers of productivity varied among colonies. Climate change projections, made using fitted models, indicated that breeding success could decline by 21 to 43% between 1961-90 and 2070-99. Climate change therefore poses a longer-term threat to kittiwakes, but as this will be mediated via availability of key prey species, other marine apex predators could also face similar threats.

How does nest box temperature affect nestling growth rate and breeding success in a parrot?

Climate change is predicted to affect many species by reducing range, habitat suitability and breeding success. Cavity-nesting species, already threatened by deforestation and declining natural hollows, may be particularly at risk because they are limited in nest-site location, and climatic alterations may further reduce usability of natural cavities. It is therefore essential to determine how cavity-users may be affected. We recorded internal nest box temperatures and modelled the relationships of four temperature parameters (relating to mean temperature, variability in temperature, low temperature extremes and high temperature extremes) with breeding success and nestling growth in an Australian cavity-nesting parrot, the Crimson Rosella (Platycercus elegans). We found that less extreme low temperatures resulted in heavier nestlings; however, higher mean temperatures tended to result in lighter nestlings. Greater temperature variability tended to reduce fledging success; however, no temperature variables had a clear effect on clutch size or hatching success. Our findings indicate that there may be a complex relationship between nestling growth and temperature, and although less extreme cold temperatures may benefit nestlings, continued increases in mean temperature and variability may have negative consequences.

The influence of age on reproductive success and diet in Australasian gannets (Morus Serrator) breeding at Pope's Eye, Port Phillip Bay, Victoria

The influence of age on reproductive success and diet was examined in ‘old’ (experienced; 12 years and older) and ‘young’ (5–8 years of age) Australasian gannets (Morus serrator) breeding at Pope’s Eye, Port Phillip Bay, Victoria during the 2002–2003 breeding period. Although food availability, as indicated by commercial fish catches, throughout this breeding period was low, there were no significant differences in breeding success or chick growth between groups. Nevertheless, old birds tended to have higher reproductive success, replacing more lost eggs and fledging chicks of a greater mass. However, old birds also laid more eggs that failed to hatch. Five fish species, including jack mackerel (Trachurus declivis), barracouta (Thyrsites atun), redbait (Emmelichthys nitidus), anchovy (Engraulis australis) and red mullet (Upeneichthys vlamingii), were important in the gannet diet during this breeding period. There were no significant differences in dietary parameters, including range of species and size of prey, between old and young gannets, nor were there any differences between those of the chicks and their parents, suggesting that adults do not forage selectively for their chicks. This study showed that even during a period of presumed low food availability, when experienced (older) birds might be expected to have enhanced success, the differences between these and less experienced (younger) birds may not be apparent.

The breeding biology of the White-faced Storm Petrel (Pelagodroma marina) on Mud Islands, Port Phillip Bay, Victoria

The White-faced Storm Petrel (Pelagodroma marina) is restricted to three breeding colonies within Victoria: Mud Islands and South Channel Fort in Port Phillip Bay, and Tullaberga Island off Mallacoota. Numbers of these storm petrels breeding on Mud Islands have declined considerably since early last century. White-faced Storm Petrels were recorded on Mud Islands from early September 2002 until mid-March 2003 when the last chicks fledged. Eggs were laid from late October to early December, with chicks hatching in the later half of December. The mean incubation period was 51.7 days (± 3.2 days (s.d.), range = 38–53, n = 13), and may have been extended by periods of egg neglect. The mean nestling period was 54.8 days (± 4.4 days (s.d.), range 50–70, n = 21). Chick growth is described. Hatching success was 54% and fledging success was 77.8%, with overall breeding success being 42%. Burrow densities were found to be influenced by plant species, vegetation height and soil moisture. The position of the burrow within the colony was shown to influence breeding success, with those nearer the edge of the storm petrel colony, closer to the marsh, and further from a colony of Australian White (Threskiornis molucca) and Straw-necked (T. spinicollis) Ibis recording higher success.

Are age-related variations in breeding performance greatest when food availability is limited?

Age-related improvements in reproductive performance in seabirds have been well documented, and may be explained by improvements in foraging efficiency or increased experience and reproductive effort with age. The interactive effects of parental age and food supply on reproductive performance, however, remain poorly understood. A widespread mass mortality of pilchards Sardinops sagax in southern Australian waters in 1998 provided a unique opportunity to investigate the effects of a sudden reduction in the availability of amajor prey species on Australasian gannets Morus serrator, an important local marine predator. Age-related differences in the breeding performance of gannets were evident in 1 year of reduced pilchard availability; when food was not limited, both young and experienced parents were equally capable of rearing chicks and had similar levels of breeding success. These data clearly demonstrate the interactive effects of parental age and food supply on breeding performance and suggest that such differences only become apparent when conditions become more stressful.

Long-term reproductive success of Australasian gannets (Morus serrator)

Life history theory predicts that individuals make trade-offs between investment in current reproduction, future reproductive potential and success in order to maximise lifetime reproductive success (LRS). Factors that may influence LRS in seabirds include delayed maturity, small clutches, high adults survivorship and long life spans. Studies have shown that reproductive success of seabirds increases with age and experience. Australasian gannets are long-lived seabirds that typically commence breeding at five or six years of age. A small colony of gannets was monitored over 12 years. This study aimed to identify patterns of long-term individual breeding biology. Results indicate that nest site, pair bond duration, age and breeding experience are all important factors in reproductive success. Relationships were found between breeding success and several variables including breeding experience, pair bond duration and nest site quality. Identifying and understanding the factors that contribute to individuals’ reproductive success is of critical importance for future conservation and management of seabird species.

Spatial and temporal variation in the breeding of Masked Lapwings (Vanellus miles) in Australia

Spatial and temporal variation in the breeding of Masked Lapwings (Vanellus miles) in Australia were examined using data from Birds Australia’s Nest Record Scheme (NRS; 1957–2002), the Atlas of Australian Birds (1998–2006), and climatic data (1952–2006). Breeding in north-western Australia was concentrated in summer, while in other regions the peak of breeding occurred during spring. Breeding success varied between regions and years but was generally highest in Tasmania. Clutch-size (mean 3.57 eggs ± 0.033 s.e., n = 549 clutches) did not vary regionally or temporally. In the north-east, breeding became earlier over time (~1.9 days per year, NRS), while in the south-east, breeding became later (~0.9 days per year); in other regions temporal trends were not evident. Only Tasmania showed a significant temporal change in breeding success (decrease of ~1.5% per year). All regions experienced warming climates, and annual rainfall increased in north-western regions and decreased in eastern regions. There were weak or no relationships between the amount or success of breeding, clutch-size and the climatic variables considered (with the possible exception of Tasmania), suggesting either that data limitations precluded us from detecting subtle effects or that Masked Lapwings have been little influenced or are resilient to changes in climate over most of their range.

Effects of snow cover on the timing and success of reproduction in high-Arctic pink-footed geese Anser brachyrhynchus

During four breeding seasons, 2003–2006, we studied the relationship between snow cover and nesting performance in pink-footed geese (Anser brachyrhynchus) in a key breeding site on Svalbard. Snow cover in late May, i.e., at the time of egg laying of geese, was derived from MODIS satellite images. Snow cover had a profound cascading effect on reproductive output via the number of nesting pairs and timing of nesting, which affected nest success, while there was only a tendency for a negative effect on clutch size. Hence, we estimated a five-fold difference in the number of young produced (to post-hatching) between years with little snow and years with high snow cover. The results from the study area correlated with whole-population productivity estimates recorded in autumn. Thus, snow cover derived from MODIS satellite images appears to provide a useful indicator of the breeding conditions in the Arctic.

Home-range, diet and breeding of a Powerful Owl Ninox strenua in East Gippsland, Victoria

Between 2004 and 2008 the diet and breeding success of a pair of Powerful Owls Ninox strenua were studied near Lakes Entrance, Victoria. In early November 2006 the adult female Powerful Owl was captured and radio-tracked for a period of 7.5 months. During this time the Owl's location was recorded on 111 occasions, including 65 nocturnal locations over 29 nights. Her home-range was calculated as 1589 ha using the Minimum Convex Polygon (MCP) method, or 871 ha based on the 95% Adaptive Kernel method. The area of forested habitat within the MCP home-range was 896 ha (the remainder representing cleared land). Her activity was centred primarily on the nesting gully where two dependent juveniles roosted, but several long-distance foraging expeditions (including roosting) that occurred more than 2.5 km from the juveniles were recorded. Arboreal mammals and birds dominated the Owls' diet. Low prey availability is suggested as being responsible for the single successful breeding event recorded in four nesting seasons.

Adaptation to urban environments promotes high reproductive success in the tawny frogmouth (Podargus strigoides), an endemic nocturnal bird species

The tawny frogmouth (Podargus strigoides) is an endemic, nocturnal bird species widespread throughout Australia with high numbers in urban environments but very limited information exists on its ability to cope with urban systems. We investigated the reproductive behaviour of this species in response to a continuum of urbanisation. Firstly, we asked does the degree of urbanisation influence the availability of suitable nesting locations. Secondly, does broad and/or local scale factors surrounding a nest influence reproductive success? And finally, does the degree of urbanisation influence time of breeding? We located 158 nest sites and monitored 189 breeding attempts across four breeding seasons (2010-2013). One hundred and thirty three of these attempts successfully fledged 177 chicks. We categorized 75 attempts as first known attempts for that season resulting in 77 fledged chicks. In some pairs, repeated attempts occurred after failure. We observed double brooding by three pairs, a strategy largely unknown in this species. Spatial modelling revealed that birds selected more vegetated areas of the gradient within which to locate their nests, avoiding more highly urbanized areas. We identified no association between land-use type and breeding success at both broad and local scales. Birds selected native rough-barked Eucalyptus tree species more frequently than other trees for nesting. The key drivers for the commencement of breeding were climatic variables, in particular rainfall. The ability of the species to synchronize breeding attempts to coincide with optimal environmental conditions resulted in extremely high reproductive success suggesting high individual fitness and an adaptation to local environmental conditions.