A national census of breeding black-billed gulls (Larus bulleri) conducted across New Zealand in 1995‒98 estimated 48,000 nests, however the methodology used was unclear. In 2013, the New Zealand threat status for the endemic black-billed gulls was changed to Nationally Critical, based on estimates of recruitment failure causing population decline. To inform future threat classification, the breeding population was re-estimated using aerial surveys to locate, photograph, and count breeding black-billed gulls across New Zealand in 2014‒2016. Large spatial gaps in nest count data during 2014/15 and 2015/16 did not allow for annual variability to be taken into account across the 3 seasons, but the 2016/17 survey successfully covered the entire country. Ground counts of nests were conducted at 16 colonies to determine a correction factor of 0.90 to apply to aerial photograph counts of apparently occupied nests. A total of 60,256 nests were found, with 33,703 nests in Southland and 20,675 nests in Canterbury. The North Island was surveyed on the ground and had 992 nests. Historical survey methods were reviewed, highlighting the inaccuracies of using nest densities or applying factors of gulls/nest to total bird counts based on photographs, as well as only counting individual birds on aerial photographs. Historical data likely overestimated numbers of breeding birds, and the inconsistencies of previous surveys make trend analyses difficult. Key recommendations for future counts include: (i) carrying out ground surveys before flights to determine the breeding stage of birds and hence the optimal time to fly; (ii) taking high resolution and zoomed in photos; (iii) carrying out ground nest counts immediately after flights to determine a correction factor; and (iv) using the same observers for all counts to maintain consistency.
Observations of activities of Hutton’s shearwaters at a natural colony in the Kōwhai River and a new colony at Te Rae o Atiu, Kaikōura Peninsula established by translocations were made during the 2014-15 and 2015-16 seasons. Weights and wing lengths of chicks at the 2 colonies taken at comparable times were similar, as were the dates of first emergence and fledging. Thus, adults flying an additional 20 km each way and climbing over 1200 m had no noticeable effect on chick growth at the mountain colony compared to the sea-level colony. Pre-fledging chicks visited other burrows as did adults at both sites, especially at Te Rae o Atiu, where a greater amount of data showed they visited other burrows throughout the season. While some adults stopped visits before fledging, others were still present after chicks had gone. Seven birds that were translocated from the Kōwhai River colony as chicks to Te Rae o Atiu in 2012 and 2013 were recorded at the Kōwhai colony and 2 of these had previously spent 1 night at Te Rae o Atiu; 28 more from the same cohorts were active at Te Rae o Atiu.
Following an initial aerial census of breeding New Zealand king shags (Leucocarbo carunculatus) in 2015, 2 further aerial censuses were carried out in 2016 and 1 census in 2017. In 2016, birds were photographed on 2 separate dates using a hand-held camera from inside a fixed wing aircraft. In 2017 the birds were photographed from a fixed-wing plane equipped with an automated camera system mounted below the aircraft. Photographs were independently assessed by 3 observers in 2016 and 2 observers in 2017. Nesting pairs were identified and the figures were averaged per colony for a final estimate of the number of active nests. The first census for 2016 was completed on 6 June and 89 active nests were estimated, compared with 117 nests counted on 1 July. For some colonies, breeding appeared to have just started in June 2016, so an underestimate of active breeders during the first aerial census was the probable cause. The 2017 aerial census was completed on 21 June and we identified 153 active nests. All follow up aerial surveys in 2016 and 2017 were well below the 187 active nests recorded in the 2015 study but within the historic variation. The exception to this trend is Trio Island, where no breeding colony was observed in 2017, the first time this has been recorded at this site.
The tendency of various species, including many Procellariiformes, to breed in sub-terrestrial burrows, complicates breeding biology studies. Artificial nest boxes facilitate detailed data collection, but may alter the buffering capacity of natural burrows, especially when these nests are exposed to direct sunlight (e.g., in non-forested habitats). We tested the buffering capacity of artificial nest boxes, equipped with additional insulating features, ex-situ in a non-forested sand dune in New Zealand. Specifically, we compared daily temperature (°C) and relative humidity (%) means, minima, and maxima between artificial nest boxes, Procellariiform burrow replicas, and ambient conditions sourced further inland using linear mixed effects models (LMMs), followed by post-hoc tests. Differences between artificial nest boxes and replicas were non-significant (P > 0.05). Our results thus showed that the applied insulating features were sufficient to retain the buffering capacities expected in natural burrows, even in exposed habitats such as sand dunes. Hence, we encourage the use of insulated artificial nest boxes in breeding biology studies targeting burrowing Procellariiformes (and other sub-terrestrially breeding species) in non-forested areas.
To investigate factors that might influence calling rates of morepork (ruru, Ninox n. novaeseelandiae), Song Meter SM2+ acoustic recorders were deployed for 12 months recording every night at Hodges Bush (a remnant forest) and Trounson Kauri Park (TKP) in Northland, New Zealand. Three call types were recorded: the classic ‘morepork’ hoot, the ‘wheel’ and ‘wok’. There was no strong seasonal variation in ‘morepork’ hoots from Hodges Bush, although there were fewer hoots from February to March. At TKP, the number of hoots declined from June to August, but the number of ‘wheel’ and ‘wok’ calls remained constant. At dusk, ‘Morepork’ hoots gradually increased until they were at their greatest frequency 3 hours after sunset at both sites. Thereafter, the number of calls reduced through the night at TKP, but remain constant at Hodges Bush until a second peak 2 hours before dawn, after which numbers drop off markedly. The other two call types were constant throughout the night at both localities, but with a pre-dawn peak at Hodges Bush. There was no significant correlation between calls and moon phase at either site. We suggest that it is possible to use vocal activity as a means of monitoring morepork population changes, but more studies are needed to determine variations between sites and different population densities.
Change in the relative abundance of grey duck (Anas superciliosa) and mallard (A. platyrhynchos) in New Zealand, from 1950 to the present day, is summarised from trapping records, hunters’ kills, and field studies. Mallards achieved numerical ascendency over grey duck throughout most of New Zealand by the late 1970s, merely 20 years after the cessation of mallard releases by historic acclimatisation societies. Post-1990, the relative abundance of mallard in almost all districts, as recorded from hunters’ kills, appears to have stabilised at 90%, or higher. Uncertainty about hunters’ and the public’s ability to discriminate between grey ducks, their hybrids with mallard, and variably-plumaged mallard females is demonstrated and most modern (post-1990) records of relative species abundance must be regarded as quantitatively suspect. Ducks identified as grey ducks by hunters are now a relative rarity throughout New Zealand, except in Northland and West Coast. Post-1990 duck trapping in North Island indicates that grey ducks, where reported, are patchily rather than generally distributed. The absence of genetically-validated criteria for discriminating ducks of grey duck x mallard hybrid ancestry continues to confound field identifications of both species.