Introduced mammalian predators induce behavioural changes in parental care in an endemic New Zealand bird

The introduction of predatory mammals to oceanic islands has led to the extinction of many endemic birds. Although introduced predators should favour changes that reduce predation risk in surviving bird species, the ability of island birds to respond to such novel changes remains unstudied. We tested whether novel predation risk imposed by introduced mammalian predators has altered the parental behaviour of the endemic New Zealand bellbird (Anthornis melanura). We examined parental behaviour of bellbirds at three woodland sites in New Zealand that differed in predation risk: 1) a mainland site with exotic predators present (high predation risk), 2) a mainland site with exotic predators experimentally removed (low risk recently) and, 3) an off-shore island where exotic predators were never introduced (low risk always). We also compared parental behaviour of bellbirds with two closely related Tasmanian honeyeaters (Phylidonyris spp.) that evolved with native nest predators (high risk always). Increased nest predation risk has been postulated to favour reduced parental activity, and we tested whether island bellbirds responded to variation in predation risk. We found that females spent more time on the nest per incubating bout with increased risk of predation, a strategy that minimised activity at the nest during incubation. Parental activity during the nestling period, measured as number of feeding visits/hr, also decreased with increasing nest predation risk across sites, and was lowest among the honeyeaters in Tasmania that evolved with native predators. These results demonstrate that some island birds are able to respond to increased risk of predation by novel predators in ways that appear adaptive. We suggest that conservation efforts may be more effective if they take advantage of the ability of island birds to respond to novel predators, especially when the elimination of exotic predators is not possible.     

Nest predators and the evolution of avian reproductive strategies: a comparison of Australian and New Zealand birds

Summary Nest predation has been considered an important factor in the evolution of avian life histories: smaller clutches and shorter incubation and nestling periods are expected where nest predation has significant effects on reproductive success. Unlike the Australian avifauna, terrestrial New Zealand birds have evolved in the absence of reptilian and mammalian predators. Here we compare the reproductive strategies of terrestrial native New Zealand birds with those of their Australian sister taxa. In 11 of 14 comparisons, New Zealand birds were larger than their Australian relatives, but we did not find any significant differences in reproductive tactics between the two regions, a result inconsistent with the nest predation hypothesis. We discuss several reasons why this may be so. One possibility is that selection imposed on avian life history tactics by mammalian predators following the arrival of humans in New Zealand has led to strategies similar to those adopted in Australia.     

Predation by mustelids and rodents on the eggs and chicks of native and introduced birds in Kowhai Bush, New Zealand

Prior to human settlement the endemic New Zealand avifauna evolved in the absence of mammalian predators. Subsequently mustelids, rodents and feral cats have become established and frequently prey on birds and nests. It has been suggested that, because of their evolutionary history, the endemic birds are especially susceptible to such predators. In this paper predation by mustelids and rodents on the eggs and nestlings of eight species of native bird is compared with that on five species of introduced European passerine inhabiting the same lowland forest.
Final outcomes were known for 101 nests of native birds and 48 nests of introduced birds found during three breeding seasons. There was no significant difference between the two groups in frequency of predation. Native birds lost 70-1% of their nests to predators and introduced birds 64-6%. Most predations occurred during the egg stage. Clutch size did not influence frequency of predation, but brood size did for Fantails and introduced birds. Stoats and weasels were responsible for 77-9% of predations on native birds and 77-4% on introduced birds; corresponding percentages for rodents (principally ship rats) were 14-7% and 19-4%. Mustelids destroyed proportionately more nests with chicks than with eggs, whereas rodents did the reverse. Predation on both groups of birds was not influenced by their nesting habitat, the species of tree used for nesting, or the height and position of the nest. The vulnerability to introduced predators of native New Zealand birds is discussed in relation to the historical declines of many species, and also their life-history patterns.     

Control of invasive predators improves breeding success of an endangered alpine passerine

Birds living in alpine environments are becoming increasingly impacted by human‐induced threats. We investigated the impacts of introduced mammalian predators on an endangered alpine species, the New Zealand Rockwren Xenicus gilviventris, and assessed whether predator control improved its breeding success. Nest monitoring revealed that the primary cause of nest failure was predation by invasive mammals, primarily Stoats Mustela erminea and House Mice Mus musculus. Daily survival rates (DSR) decreased with nest age, and nests were at their most vulnerable to predators just prior to fledging. DSR, egg‐hatching and fledgling rates were all improved by predator trapping, demonstrating the significant impacts that even low numbers of invasive predators can have on sensitive alpine and upland species.     

Effect of the blood-sucking mite

Pathological consequences of the blood-sucking mite Ornithonyssus bursa vary between species, with its impact ranging from no measurable effect, to significant blood loss and chick mortality. In New Zealand, where several bird species are known to be parasitised by O.bursa, the effect of this mite on host fitness is unclear, as few studies have been carried out. During a three-year study of the North Island robin Petroica longipes on Tiritiri Matangi Island, the prevalence of O. bursa in robin nests and on chicks and its impact on robin chick growth and survival was measured. The presence of mites was correlated with both time of the season and humidity of the habitat, with infestation being positively correlated with later nesting attempts and more humid microclimates. Robin chicks in infested nests were significantly smaller and fledged at an earlier age than chicks in nests where no mites were detected. Despite this effect, no significant difference in body size or survival was detected between the two groups at one month post-fledging. This was most likely because chicks from mite- infested nests compensated for their retarded growth once they left the nest environment. On mainland New Zealand, where ground-dwelling mammalian predators are present, chicks forced to leave the nest at an earlier age with less developed flying skills may be at an increased risk of predation.     

Effects of Mesopredators on Nest Survival of Shrub-Nesting Songbirds

ABSTRACT Although nest predation is often the single largest source of mortality in avian populations, manipulative studies to determine predator impacts on nest survival are rare, particularly studies that examine impacts of mid-size mammalian predators (hereafter, mesopredators) on nest survival of shrub-nesting birds. We quantified nest survival and identified nest predators of shrub-nesting songbirds within 4 large (approx. 40-ha) exclosures and 4 control sites within a longleaf pine (Pinus palustris) ecosystem. During 2003–2006, we located and monitored 535 shrub nests (222 with videography) for 4,804 nest-days to quantify daily nest survival and document predation events. We found no support for a treatment effect, suggesting mesopredators had little impact on daily nest survival (0.9303 in controls and 0.9260 in exclosures) of shrub-nesting songbirds. For the 5 most commonly monitored species, daily nest survival within species was constant. Our analysis suggested that shrub nests were most vulnerable during the nestling stage and presence of cameras on nests increased survival with the increase in survival being more pronounced during the incubation stage. We filmed 107 nest predation events, identifying predators at 88 nests. Of these 88 nests, snakes caused 33%, red imported fire ants (hereafter fire ants, Solenopsis invicta) 28%, raptors 17%, corvids 8%, mesopredators 6%, and small mammals 8% of nest predations. Cause-specific nest predation in controls and exclosures did not differ from expectation, providing evidence that compensatory predation did not occur. Nest predators differed from expectation with regard to nest stage; fire ants and raptors only depredated nests during the nestling stage. Presence of cameras had no effect on nest abandonment. Fire ants were the most prevalent nest predator, and nest predation by fire ants was only observed on nestlings, potentially reducing likelihood of renesting. Magnitude and timing of fire ant predation suggests that fire ants may be the most influential nest predator of shrub-nesting birds within the longleaf pine ecosystem. Our data suggest that controlling mesopredators will have no effect on nest success of shrub-nesting birds within longleaf pine forests.     

Feathers to Fur: the status of New Zealand ecological research in 2009

We outline the scope of this special issue of New Zealand Journal of Ecology, which reviews progress in New Zealand ecology to 2009, based on a symposium in 2007. Both the issue and symposium update a 1986 conference and 1989 special issue of NZ J Ecol called ?Moas, Mammals and Climate? which has been influential and widely cited. This issue revisits several themes featured in 1989, including the extent of recent and prehistoric extinctions in the New Zealand fauna; effects of introduced mammalian herbivores replacing now-extinct browsing birds such as moa; the impacts of introduced mammalian predators on native birds (hence the Feathers to Fur title); the role of islands as refuges and opportunities for restoration; and the status of bird?plant mutualisms like pollination and fruit dispersal. Several topics not discussed in 1989 are raised, including the unusual size and functional composition of New Zealand?s tree flora, and several taxonomic groups (invertebrates, fungi) and habitats (fresh waters) that received little attention in 1989. We summarise four symposium talks which are not included elsewhere in this issue. New Zealand leads the world in ways both unenviable (e.g. levels of impact of introduced species) and enviable (e.g. predator eradication, translocations, rare species management. The recent advances reviewed in this issues have relevance well beyond New Zealand.     

Breeding and survival of New Zealand Pigeons Hemiphaga novaeseelandiae

The breeding and survival of New Zealand Pigeons Hemiphaga novaeseelandiae were studied by radiotelemetry at three contrasting native forest sites in the North and South Islands of New Zealand. At each site, mean annual productivity was low (0-0.12 fledglings/adult) in relation to the mean annual rate of adult mortality (0.18-0.53). Losses of eggs and chicks to introduced mammals were the main identified causes of nest failure. Causes of adult mortality included episodic predation by introduced mammals and apparent starvation in spring at one site. At the most intensively-studied site (Pelorus Bridge), where 75 birds were radiotagged over 7 years, there was a marked annual variation in breeding success (0-0.3 fledglings/adult), including one season (1986–1987) when no breeding activity was detected at all. New Zealand Pigeons were legally hunted in the past, but our results indicate that harvesting is unlikely to be sustainable under current ecological conditions.     

Using artificial nests to predict nest survival at reintroduction sites

Artificial nests are frequently used to assess factors affecting survival of natural bird nests. We tested the potential for artificial nests to be used in a novel application, the prediction of nest predation rates at potential reintroduction sites where exotic predators are being controlled. We collected artificial nest data from nine sites with different predator control regimes around the North Island of New Zealand, and compared the nest survival rates with those of North Island robin (Petroica longipes) nests at the same sites. Most of the robin populations had been reintroduced in the last 10 years, and were known to vary in nest survival and status (increasing/stable or declining). We derived estimates of robin nest survival for each site based on Stanley estimates of daily survival probabilities and the known incubation and brooding periods of robins. Estimates of artificial nest survival for each site were derived using the known fate model in MARK. We identified the imprints on the clay eggs in the artificial nests, and obtained different estimates of artificial nest survival based on imprints made by different potential predators. We then compared the value of these estimates for predicting natural nest survival, assuming a relationship of the form s = αpβ, where s is natural nest survival and p is artificial nest survival. Artificial nest survival estimates based on imprints made by rats (Rattus spp.) and brushtail possums (Trichosurus vulpecula) were clearly the best predictors (based on AICc), and explained 64% of the variation in robin nest survival among sites. Inclusion of bird imprints in the artificial nest survival estimates substantially reduced their predictive value. We suggest that artificial nests may provide a useful tool for predicting the suitability of potential reintroduction sites for New Zealand forest birds as long as imprints on clay eggs are correctly identified.     

Alien predators are more dangerous than native predators to prey populations

Alien predators are widely considered to be more harmful to prey populations than native predators. To evaluate this expectation, we conducted a meta-analysis of the responses of vertebrate prey in 45 replicated and 35 unreplicated field experiments in which the population densities of mammalian and avian predators had been manipulated. Our results showed that predator origin (native versus alien) had a highly significant effect on prey responses, with alien predators having an impact double that of native predators. Also the interaction between location (mainland versus island) and predator origin was significant, revealing the strongest effects with alien predators in mainland areas. Although both these results were mainly influenced by the huge impact of alien predators on the Australian mainland compared with their impact elsewhere, the results demonstrate that introduced predators can impose more intense suppression on remnant populations of native species and hold them further from their predator-free densities than do native predators preying upon coexisting prey.     

Trial reintroduction of buff weka to an unfenced mainland site in central South Island,New Zealand

While there have been significant conservation successes through restoration of island biodiversity following the eradication of invasive predators, a major challenge remains to reintroduce native species within larger mainland systems that support suites of introduced mammalian predators. Strategies to enhance establishment and persistence of reintroduced populations include pre‐release management to reduce post‐release dispersal, and habitat restoration such as predator control at release sites. Evaluation of such strategies critically requires strategic and intensive post‐release monitoring to identify drivers of success or the specific causes of failures. The buff weka (Gallirallus australis hectori), a flightless rail, was reintroduced to an unfenced mainland island on New Zealand's South. Past reintroductions on the mainland have all failed, but lack of post‐release monitoring has meant the exact cause and timing of failures is unknown. We investigate the ability of buff weka to establish a mainland population in conjunction with high intensity predator control. Nineteen buff weka (15 males, 4 females) were transferred from predator‐free islands in Lake Wakatipu, South Island, to Motatapu Station and held in a pre‐release enclosure for 6 weeks. Using a combination of very high frequency (VHF) and Global Positioning System (GPS) telemetry, released birds were monitored every 2 days for 4 months post‐release. Following release, no buff weka dispersed off Motatapu Station. Survival, however, was low and by the end of the study, 12 (63%) buff weka had been predated by introduced mustelids, ferrets (Mustela furo) and stoats (Mustela erminea). The lack of dispersal by buff weka suggests the presence of favourable resources on Motatapu Station. However, the low survival rate indicates that the predator‐trapping network was insufficient to suppress predator numbers to a level low enough for buff weka population persistence.     

Losing anti‐predatory behaviour: A cost of translocation

Translocation of endangered species to habitats where exotic predators have been removed is now a common conservation practice around the world. Many of these translocated populations have thrived, and they are often used as sources for the harvesting of individuals for translocations to sites where exotic predators still exist, albeit at reduced densities. This study investigates how isolation from exotic predators affects the ability of individuals to recognize such predators using the North Island robin (Petroica longipes) as a model. The study was carried out in three robin populations in the North Island, New Zealand: a translocated population on Tiritiri Matangi Island, where exotic mammalian predators are absent; a population reintroduced from Tiritiri Matangi Island to Wenderholm Regional Park, a mainland site where these mammals are controlled to low densities; and a mainland population at Benneydale where exotic predatory mammals are common. The response intensity of robins to a model stoat was high at Benneydale and low at Tiritiri Matangi and Wenderholm. This result indicates that isolation from mammalian predators on Tiritiri Matangi has suppressed the ability of North Island robins to recognize these predators. It is possible that the low predatory mammal densities at Wenderholm have reduced robin contact with stoats, therefore reduced the opportunity for robins to learn to recognize stoats. Thus, translocation of individuals from populations without predators to places where key predators still exist could be unsuccessful if translocated individuals fail to perform appropriate anti‐predator behaviours.     

Responses of kukupa (

The kukupa or New Zealand pigeon (Hemiphaga novaeseelandiae) is gradually declining on the New Zealand mainland, due mostly to predation by introduced pest mammals including ship rats (Rattus rattus) and brushtail possums (Trichosurus vulpecula). We report on a co-operative project between Maori landowners, the Department of Conservation, and Manaaki Whenua–Landcare Research researchers to restore a Northland kukupa population and to examine kukupa nesting success in relation to pest abundance. Ship rats and possums were targeted by trapping and poisoning throughout Motatau Forest (350 ha) from 1997 to 1999; only possums were targeted in 2000. All 13 kukupa nests located before pest control started in late 1997 failed at the egg stage, but all seven nests located in 1998–99 successfully fledged young when trapping and tracking indices of possums and ship rats were less than 4%. After pest control, counts of kukupa and some other bird species increased at Motatau compared with counts in a nearby non-treatment block, suggesting numbers of adult kukupa can be increased in small forest areas by intensive pest control. This increase is due at least partly to increased nest success. Evidence from time-lapse video cameras, sign remaining at nests, and nest success rates under different pest control regimes suggest both ship rats and possums are important predators at kukupa nests.     

Low outcrossing rates and shift in pollinators in New Zealand pohutukawa (Metrosideros excelsa; Myrtaceae)

New Zealand pohutukawa (Metrosideros excelsa), a member of the Myrtaceae, is a large, mass-flowering tree endemic to northern New Zealand coastlines. Mainland populations have been reduced to fragmented stands, and the original suite of bird pollinators has been largely replaced by introduced species. The native pollinator fauna on several offshore islands is largely intact and includes three species of the New Zealand honeyeaters (Meliphagidae) and native, solitary bees. We estimated multilocus outcrossing rates for three mainland and two island populations and found that they were among the lowest in the Myrtaceae (t(m) = 0.22-0.53). The shift in pollinators had no measurable effect on the mating system. Mass-flowering facilitates geitonogamous selfing, and inbreeding depression in seedling height was detectable at 6 mo of growth. F(s) [Wright's (1965) Fixation Index] was consistently higher than F(m) in all populations, indicating that selection may eliminate selfed offspring from populations prior to achieving reproductive maturity. Results suggest that increased selfing in mainland populations due to pollinator changes is not responsible for current patterns of poor regeneration of this species.     

Isolation from mammalian predators differentially affects two congeners

Evolutionary isolation from predators can profoundly influencethe morphology, physiology, and behavior of prey, but littleis known about how species respond to the loss of only someof their predators. We studied antipredator behavior of tammarwallabies (Macropus eugenii) and western gray kangaroos (Macropusfuliginosus) on Kangaroo Island (KI), South Australia, andat Tutanning Nature Reserve on the mainland of western Australia.Both species on KI have been isolated from native mammalian predators for several thousand years. On KI, wallabies (becauseof their size) are vulnerable to diurnal aerial predators.In contrast, on the mainland both species have been exposedcontinuously to native and introduced mammalian and avian predators.At both locations, wallabies modified the amount of time they allocated to vigilance and foraging in response to group size,whereas kangaroos did so only at the higher risk Tutanningsite. Both species modified overall time budgets (they werewarier at the higher risk site), and both species modifiedspace-use patterns as a function of risk. At the higher risk site, tammars were closer to cover, whereas kangaroos were,on average, farther from cover. We hypothesize that the presenceof a single predator, even if it is active at a different timeof day, may profoundly affect the way a species responds tothe loss of other predators by maintaining certain antipredatorbehaviors. Such an effect of ancestral predators may be expected as long as species encounter some predators.     

Native plant/herbivore interactions as determinants of the ecological and evolutionary effects of invasive mammalian herbivores: the case of the common brushtail possum

In their native range, mammalian herbivores exist in a suite of direct and indirect ecological and evolutionary relationships with plant populations and communities. Outside their native range these herbivores become embedded in a multitude of new ecological and evolutionary interactions with native plant species in the new range. Sound knowledge of the plant/herbivore interactions in the herbivores’ native range provides an ideal framework to better understand their effects in the introduced range. The example of the common brushtail possum (Trichosurus vulpecula) and its introduction to New Zealand from Australia provides an excellent case study. In Australia, the common brushtail possum is a widespread generalist herbivore and it is thought that this generalist lifestyle has equipped the species well for successful colonisation of New Zealand. In Australia the brushtail possum has co-existed with highly chemically defended foliage since the Oligocene and recent papers have supported the role of possums as agents of selection on eucalypt defences. While the chemical profile of New Zealand foliage is comparatively poorly understood, possums do show clear selectivity between and within populations and some of these interactions may be mediated by the animals ability to ‘cope’ with PSMs, coupled with maintaining its generalist diet. While possums have had less time to effect evolutionary change in New Zealand species, their impacts on plant fitness have been well documented. However, further knowledge on variation and heritability of foliage traits driving possum preferences is needed to elucidate the ecological and evolutionary plant/possum interactions in the invasive range.     

Large mainland populations of South Island robins retain greater genetic diversity than offshore island refuges

For conservation purposes islands are considered safe refuges for many species, particularly in regions where introduced predators form a major threat to the native fauna, but island populations are also known to possess low levels of genetic diversity. The New Zealand archipelago provides an ideal system to compare genetic diversity of large mainland populations where introduced predators are common, to that of smaller offshore islands, which serve as predator-free refuges. We assessed microsatellite variation in South Island robins (Petroica australis australis), and compared large mainland, small mainland, natural island and translocated island populations. Large mainland populations exhibited more polymorphic loci and higher number of alleles than small mainland and natural island populations. Genetic variation did not differ between natural and translocated island populations, even though one of the translocated populations was established with five individuals. Hatching failure was recorded in a subset of the populations and found to be significantly higher in translocated populations than in a large mainland population. Significant population differentiation was largely based on heterogeneity in allele frequencies (including fixation of alleles), as few unique alleles were observed. This study shows that large mainland populations retain higher levels of genetic diversity than natural and translocated island populations. It highlights the importance of protecting these mainland populations and using them as a source for new translocations. In the future, these populations may become extremely valuable for species conservation if existing island populations become adversely affected by low levels of genetic variation and do not persist.     

Predation and other factors currently limiting New Zealand forest birds

Holdaway (1989) described three phases of historical extinctions and declines in New Zealand avifauna, the last of which (Group III, declining 1780?1986) was associated with European hunting, habitat clearance, and predation and competition from introduced European mammals. Some forest bird species have continued to decline since 1986, while others have increased, usually after intensive species-specific research and management programmes. In this paper, we review what is known about major causes of current declines or population limitation, including predation, competition for food or another resource, disease, forest loss, and genetic problems such as inbreeding depression and reduced genetic variation. Much experimental and circumstantial evidence suggests or demonstrates that predation by introduced mammals remains the primary cause of declines and limitation in remaining large native forest tracts. Predation alone is generally sufficient to explain the observed declines, but complex interactions between factors that vary between species and sites are likely to be the norm and are difficult to study. Currently, the rather limited evidence for food shortage is mostly circumstantial and may be obscured by interactions with predation. Climate and food supply determine the number of breeding attempts made by herbivorous species, but predation by introduced mammals ultimately determines the outcome of those attempts. After removal of pest mammals, populations are apparently limited by other factors, including habitat area, food supply, disease or avian predators. Management of these, and of inbreeding depression in bottlenecked populations, is likely to assist the effectiveness and resilience of management programmes. At the local or regional scale, however, forest area itself may be limiting in deforested parts of New Zealand. Without predator management, the number of native forest birds on the New Zealand mainland is predicted to continue to decline.     

Increased nest defence of upland‐nesting ducks in response to experimentally reduced risk of nest predation

Parent birds should take greater risks defending nests that have a higher probability of success. Given high rates of mammalian nest predation, therefore, parents should risk more for nests in areas with a lower risk of mammalian predation. We tested this hypothesis using nest defence data from over 1300 nests of six species of dabbling ducks studied in an area where predation risk had been reduced through removal of mammalian predators. When predator removal reduced nest predation, the ducks increased risk taking as predicted. Also as predicted, risk taking varied inversely with body size, an index of annual survival, among species. For ducks to vary nest defence in response to variation in predation risk they must be able to assess the risk of nest predation. Because ducks modified nest defence in the breeding season immediately following predator removal, ducks may be able to assess predator abundance indirectly (e.g. by UV reflection from urine) rather than by seeing or interacting directly with the predators.     

Demography of takahe (

The last remaining natural population of the critically endangered takahe (Porphyrio hochstetteri) is confined to the Murchison Mountains in Fiordland, New Zealand. This mainland population contains about half of the c.?300 remaining takahe and benefits from one of the costliest recovery programmes in the country. Management activities include deer culling, stoat trapping, nest manipulation (e.g. removal of infertile eggs) and captive rearing of chicks. To determine what effect this intensive management has had on the recovery of the Fiordland takahe population, we modelled 25 years of survival and breeding success data as a function of environmental factors (e.g. precipitation, temperature, beech seedfall, tussock flowering) and specific management activities (egg manipulation, captive rearing, stoat control). Annual adult survival, estimated at 78% (credibility interval (CI) = 75?81%), is significantly increased to 85% (76?92% CI) in presence of stoat trapping, but is still low relative to introduced takahe populations on offshore islands and other large New Zealand bird species in predator-free environments. This suggests that the harsh environment of Fiordland may be suboptimal habitat in terms of survival for takahe. On the other hand, reproductive output in Fiordland is similar to that for introduced island populations, and is improved even further by management. Number of chicks per pair fledged with nest manipulation and captive rearing is estimated at 0.66 compared with 0.43 in the absence of nest management. The difference is explained mainly by low fledging success in the wild, especially for double clutches, which justifies the practice of removing one of two viable eggs and transferring it to a captive-rearing facility. The results of this study indicate that current management activities such as stoat trapping and captive rearing have a strong positive effect on population growth of the Murchison Mountains takahe population.