Assumptions and predictions concerning movements of Night Parrots, as discussed by the Night Parrot Recovery Team on 11 October 2016.
Allan Burbidge
Chair, Night Parrot Recovery Team
12 October 2016
The following information is intended to inform assumptions about distances that a Night Parrot may travel either regularly or in response to weather-driven resource availability across the landscape. Besides the recent measurements of direct and cumulative minimum distances travelled, there is a set of assumptions that are reasonable to make about likely and potential movements.
Information concerning distances travelled between roosts and nests on the one hand and water, and feeding sites on the other, are hardly well-known for most Australian birds, let alone parrots and the Night Parrot specifically. We stress that any discussion of the topic must emphasize that such distances are variables that will have means and (probably) large variances driven by variation in seasonal conditions that may happen over short or long time frames.
Much of the following discussion is based on empirical data related to two tracking sessions – one GPS and one VHF radio – in 2015 and 2016. It also includes comprehensive habitat surveys conducted in mid-2016. The final analyses and compilation of these data is nearing completion. Until such time as this becomes available, the Night Parrot Recovery Team believes that the following discussion is an accurate reflection of current knowledge. It is also important to note that future work planned that involves tracking individuals at other times may alter or corroborate some of the assumptions stated below.
Movements and habitats
A GPS tag worn by a male night parrot was programmed to acquire GPS fixes in two “series” per night for five nights. 127 points were logged that clustered into 18 sites. Inferred behaviours at the sites included roosting, foraging and drinking. Excluding series one on night one (when the bird was still settling from capture) and series nine and ten (which were less than 2 hrs), the mean distance moved within each of the remaining seven two-hour series was 8.9 km (s.d. = 5.3 km; max. = 17.62 km; min. = 1.3 km). The maximum distance between fixes within a series was 6.3 km between two locations that were logged 10 minutes apart.
The following descriptive statistics also exclude night one: the mean minimum cumulative distance moved per night was 29.9 km (s.d. = 9.6 km; max. = 41.18 km; min. = 17.82 km). The maximum straight-line distance the bird was recorded away from the roost was 9.4 km. The nightly mean minimum convex polygon (MCP) was 783 ha (s.d. = 605 ha; max. = 1821 ha; min. = 305 ha). The total MCP area for all points was 3,344 ha.
The roost site was located in Triodia longiceps at the base of a low sandstone range. In the early morning of one night, the bird travelled a minimum of 9 km in a round trip from and back to a feeding area (that was itself was approx. 4 km from the roost site) to drink. This is of similar magnitude to comments made by Andrews (1883) who stated that birds can fly up to 6.5-8 km to water. Apart from the drinking site, the remaining 16 sites encompassed six broad land types. Three sites were situated on a floodplain which is periodically inundated. This included one extensive plain dominated by ephemeral species and two small patches of Astrebla grassland on the edge of the floodplain. One site was located within a broad alluvial depression fed by local run-off from nearby hills. One was on stony rises close to a sandstone mesa, two were in pebbly herbfields, and the remaining nine sites were situated on undulating ironstone plains dotted with vegetated patches (gilgais and small drainage channels) of varying sizes. In addition to these habitats, the female Night Parrot that was tracked using a VHF radio tag was detected in quaternary sand drifts and ridges.
The GPS tag data was collected from one bird in a productive season. Given that resources (food and water) are likely to be both scarce and patchy in drought conditions, it is reasonable to expect that at least some Night Parrots may travel 100 km or more in a night, by the time they return to their roost. Heavy grazing by e.g. cattle or macropods, might also simulate resource availability under drought conditions.
Information about dispersing juvenile (first year) Night Parrots is not available. Juveniles of the related Western Ground Parrot (Pezoporus flaviventris) are known to move at least several tens of kilometres from known areas of residence (Gilfillan et al. 2006); for the Eastern Ground Parrot (P. wallicus), the longest estimated movement is 220 km (Higgins 1999: 596) and presumably dispersing young birds have been found dead in towns with no suitable habitat nearby. Given these observations in Eastern Ground Parrots, for a related species living in the arid zone like Night Parrots, dispersal movements of up to a few hundred kilometres would not be surprising.
Flight behaviour
Both birds involved in the radio- and GPS-tag work were captured in standard mist-nets approx. 1.5 m and 0.6 m above ground. Multiple observations of these and other individuals show that Night Parrots are swift on the wing. Three individuals recently observed using night vision equipment flew at fast speeds akin to Common Bronzewings (Phaps chalcoptera) or Australian Hobbies (Falco longipennis).
Nomadism
Nomadic behaviours in Night Parrots are poorly understood. The literature contains speculation that dispersal/nomadism may occur, and several authors have hypothesised that Night Parrots may move from Triodia areas during wet periods into chenopod systems during dry periods, although the population at Pullen Pullen has persisted through dry and wet times (see Higgins 1999; Murphy et al. 2015; TSSC 2016 and references therein). It seems reasonable to assume that some populations may be largely sedentary and some populations may have nomadic movements and that apparently sedentary populations may be nomadic at times.
Conclusion
Based on the data summarised above, the Night Parrot Recovery Team believes that it is reasonable to assume that:
- during productive seasons Night Parrots may fly cumulative distances of up to 100 km per night for movements between roosts and foraging and drinking areas,
- during drought conditions, it is possible that Night Parrots may fly cumulative distances that are considerably greater than 100 km per night,
- during adult or juvenile dispersal or nomadic movements, Night Parrots may travel distances in the order of several hundred kilometres,
- Night Parrots fly low and fast between roosting, foraging and drinking locations, and
- Foraging areas include highly productive and floristically diverse alluvial habitats, pebbly herbfields, sparse ironstone pavements, and quaternary sand drifts and ridges.
References
Andrews, F. W. (1883). Notes on the Night Parrot. Transactions and Proceedings of the Royal Society of South Australia 6, 29–30.
Gilfillan, S., Comer, S., Burbidge, A. H., Blyth, J., and Danks, A. (2006). Addendum to South Coast Threatened Birds Recovery Plan. South Coast Threatened Birds: Background Information, Species-specific Recovery Plan and Area-based Management Plan. Western Ground Parrot (Pezoporus wallicus flaviventris), Western Bristlebird (Dasyornis longirostris), Noisy Scrub-bird (Atrichornis clamosus), Western Whipbird (western heath) (Psophodes nigrogularis nigrogularis), Western Whipbird (western mallee) (Psophodes nigrogularis oberon), Rufous Bristlebird (western) (Dasyornis broadbenti litoralis). Report produced for the South Coast Threatened Birds Recovery Team, Albany.
Higgins, P. J. (1999). ‘Handbook of Australian, New Zealand and Antarctic Birds. Vol. 4. Parrots to Dollarbird’. (Oxford University Press: Melbourne.)
Murphy, S., and the Night Parrot Recovery Team (2015). Shining a light: the research unlocking the secrets of the mysterious Night Parrot. Australian Birdlife 4(3), 30–35.
Threatened Species Scientific Committee (2016). Conservation Advice Pezoporus occidentalis Night Parrot. Department of the Environment, Canberra, ACT.