We found widespread nesting on the ground in a large population of feral rock pigeons (Columba livia) in an urban, but predator-free native forest reserve in Christchurch, New Zealand. Ninety-seven percent (n = 77) of rock pigeon nests were located on the ground, with most placed either at the bases of large kahikatea (Dacrycarpus dacrydioides) trees or under a tangle of vines on the forest floor.
Clutch size was 2 eggs in all nests, with a hatching success of 93.9% in nests that survived to the hatch stage. Overall nest success was higher (60.0%) than in other populations of rock pigeons, with half of nest failures attributed to culling of the population that occurred during the course of our study. On average, rock pigeons fledged 1.60 chicks per successful nest. No ground nests were located outside the boundary of the predator- proof fence, suggesting pigeons were able to assess predation risk when selecting nest site location. Ground nesting by rock pigeons may be a way to avoid damage to nests in the canopy by strong winds or predation from aerial predators such as harrier (Circus approximans), which also occur in the reserve. Based on density of nests, we estimated a breeding population of 226 to 258 rock pigeons in the 7.8 ha reserve. The high number of pigeons in the reserve highlights the need for further studies on how populations of introduced species of birds in New Zealand respond to control of mammalian predators and the effect this may have on sympatric native species.
Aggressive interactions among species competing for resources are common and usually asymmetric, leading to consistent dominance hierarchies. Here, we document aggressive interactions among six albatross and three petrel species off southern New Zealand, in response to supplemental food provided by ecotourism boats. For species with sufficient sampling, we found a consistent dominance hierarchy, with Diomedea antipodensis gibsoni > D. epomophora > Macronectes halli > Thalassarche cauta > T. salvini > T. bulleri > Daption capense. The heavier species was dominant in most species pairs. Dominant species monopolised the food provided by displacing subordinates. However, subordinate species appeared to gain access to some food through fast responses, greater manoeuvrability, and feeding on small pieces of food ignored by dominants. Similar congregations and interactions at natural food sources suggest that dominance hierarchies may play an important role in structuring the diverse seabird communities in the southern oceans.
Birds were banded in gardens at Rangiora 1961–1977, Christchurch 1977–2000, and Kaikōura 2000–2016. In total, 21,565 birds of 14 species were captured in mist-nets or traps and banded; 3,213 individuals were recovered or recaptured. The most common species banded was silvereye (Zosterops lateralis lateralis) with 15,349, followed by house sparrow (Passer domesticus domesticus) with 4,497, and common starling (Sturnus vulgaris vulgaris) with 430; all other species were less than 300 birds banded which is less than five birds per year. Distance recoveries of note are: silvereyes – Kaikōura to Wellington (153.0 km), Rangiora to Greymouth (146.0 km), Rangiora to Otira (99.0 km), with two more birds over 25.0 km; house sparrow – Christchurch to Homebush (43.5 km), with two more over 25.0 km; common starling – Rangiora to Christchurch (27.8 km); dunnock (Prunella modularis) – local movement (5.1 km). The most significant recoveries from time of banding to recovery are: silvereye – 8.8 years; house sparrow – 8.7 years; starling – 8.0 years; dunnock – 5.3 years. Wing length and mass measurements of Kaikōura birds were generally within published ranges.
In October 2019, an expedition to the subantarctic Bounty Islands provided the opportunity to conduct comprehensive ground counts of erect-crested penguins to assess population size and compare numbers to previous surveys. The entirety of Proclamation Island, an erect-crested penguins’ stronghold, was surveyed and number of active penguin nests was determined via ground counts. Drone surveys aiming at assessing seal numbers, provided high- resolution aerial photography allowing spatial analysis of penguin nest densities on four islands, i.e. Proclamation, Tunnel, Spider, and Ranfurly Islands. A total of 2,867 penguin nests were counted on Proclamation Island between 24 and 29 October. Adjusting for the earlier timing of the survey compared to counts conducted since 1997, nest numbers were only marginally lower (~2.4%) than in 1997 and 2004 suggesting that the penguin population has remained stable for the past 20 years; a ~10% reduction in penguin numbers in 2011 seems to be related to warmer than average ocean temperatures that year. Density analysis from drone imagery showed highly heterogenous distribution of penguin nests, with birds preferring areas sheltered from prevailing south-westerly winds. This also means that a previous estimate from 1978 which relied on uniform extrapolation of nest densities to what was assumed to suitable breeding areas substantially overestimated the true population size, thereby contributing to the species current ‘endangered’ threat ranking.
The New Zealand Threat Classification System is used to prioritise and evaluate conservation programs, as an advocacy tool for biodiversity and as a guide to risk when assessing the severity of effects of development. A lack of transparency and adherence to scientific conventions when compiling the listings for birds led to previous criticism (Williams 2009). Two recent papers provide sufficient information to independently assess the threat status ranking of two endemic birds. Both papers provide detailed information on multiple sites and assess the influence of different threats. Both also provide an estimate of population size and generation time as required for assigning a Threat Classification. The authors conclude with clear recommendations on appropriate New Zealand and IUCN threat status ranking in both papers. We consider that the authors have failed to consistently apply the criteria for assessment in the Threat Classification Manual (Townsend et al. 2008) and IUCN Red List Guidelines (IUCN 2019). We re-evaluate the recommended threat status in light of adherence to the criteria, the data used and the analysis methodology selected. We recommend greater transparency, use of additional methodology and adherence to the guidelines to improve consistency and reliability of threat status classification.
Thirty breeding colonies of three petrel species were found on 23 of 41 islands and one of three headlands surveyed between Milford Sound/Piopiotahi and Dagg Sound/Te Rā in Fiordland National Park, New Zealand, in November 2020. Sooty shearwater (Ardenna grisea) was the most widespread and abundant species, with an estimated 7,300 burrows on 20 islands and one mainland site. Broad-billed prions (Pachyptila vittata) were found breeding on five islands (600 burrows estimated), including an islet in Poison Bay, 70 km north-east of their previous northernmost Fiordland breeding location. We record the first evidence of mottled petrels (Pterodroma inexpectata) breeding in Doubtful Sound/Patea (on Seymour Island), which is now their northernmost breeding location. When combined with data from surveys in southern Fiordland between 2016 and 2021, more than 66,000 pairs of petrels are estimated to be present in 168 colonies in Fiordland. This total comprises 42,100–52,400 sooty shearwater pairs, 11,700–14,500 broad-billed prion pairs, 5,090–6,300 mottled petrel pairs, and at least 1,000 common diving petrel (Pelecanoides urinatrix) burrows. This is the first near-complete estimate of petrel population sizes for the Fiordland region.
Swiftlets (Collocalia, Aerodramus) make up a guild of birds which prey on a wide range of aerial insects and spiders. The studies reviewed here show their prey to include 19 orders and 55 families of insects plus spiders. Most swiftlets seem to take whatever is available at the time and place, with site to site and year to year differences noted. One species (black-nest swiftlet) appears to be a swarm-feeding specialist. Prey size ranged from <1 to 13 mm in body length and is related to swiftlet body size. Habitat and elevational differences may represent resource partitioning in foraging strategies.
This paper presents the results of four censuses of the northern New Zealand dotterel (Charadrius obscurus aquilonius) population undertaken between 1989 and 2011. During that period, the population increased by roughly 50%, from about 1,320 to about 2,130 birds. Most birds (85%) were in the northern part of the North Island (Northland, Auckland, and Coromandel Peninsula), but the taxon is expanding its range southwards on both the west and east coasts. On the east coast, a few pairs are now breeding close to Cook Strait. Population trends varied between regions, and almost all of the overall increase was a result of increases on the east coast. The highest rates of increase were on the Auckland east coast and on Coromandel Peninsula, probably because the intensity of management has been highest in those regions. In the Auckland urban area, birds now routinely breed inland, mainly on grass or bare earth; elsewhere, the taxon is almost entirely coastal. The proportion of birds on the west coast has fallen over the past 50 years, and about 85% of the taxon is now found on the east coast. If the overall increase in numbers has continued at the same rate since 2011, there would be about 2,600 birds in 2020. The size of the population and its rate of increase justify the recent down-listing of the subspecies to a threat ranking of At Risk (Recovering), but it remains Conservation Dependent. The recovery programme has been highly successful, and most management of the taxon is now undertaken by community groups, regional councils, and volunteers. Continuing threats include predation, flooding of nests, and disturbance during breeding; in future, continuing coastal development and increased recreational activity will probably degrade habitat further, particularly on the east coast, and climate change will have a range of impacts.