Bird monitoring in a tropical savanna conservation reserve suggests Noisy Miners Manorina melanocephala and adaptive fire management should be a future management focus

Long-term monitoring of bird communities over time can provide important data for management, and the adaptation of that management over time. We examined data from bird surveys across 37 sites sampled in five different years from 2009 to 2017 in a 56,000-ha tropical savanna conservation reserve, in northern Queensland. Because of the limitations of the survey method and the lack of environmental data for sites, we examined broad patterns in the abundance of small- and large-bodied birds, abundance of Noisy Miners Manorina melanocephala, land type, survey year, and time since last fire. There was some variation in bird species richness and abundance across the land types, years sampled and Noisy Miner abundance; however, the clearest pattern was decreasing numbers of small-bodied birds and increasing Noisy Miner abundance, and an association between time since fire (i.e. <3 years, >5 years), Noisy Miner abundance and diversity in other birds. The apparent and potentially compounding interaction of Noisy Miners and fire could be an emerging problem. Future fire management needs to be embedded in a program of targeted question-driven monitoring and adaptive management, to provide more assured approaches to prescribed burning that enhances bird conservation.

The distribution and frequency of detection of woodland birds after selective logging of a small woodland remnant in an agricultural landscape in inland southern Australia

The majority of studies into the response of birds to logging in Australian forests has been done in forest-dominated landscapes or relatively large forest blocks, where the surrounding landscape can ameliorate impacts. This is the first study to examine the response of birds to logging of a small, relatively isolated woodland remnant in a landscape dominated by agriculture, with a focus on declining woodland birds. Approximately two thirds of a 120 ha cypress-eucalypt woodland remnant was selectively logged. Eighty bird species in total were recorded 2–3½ years after logging, including 18 recognised as declining woodland birds. Sixty-four species were recorded in the unlogged area and 72 in the logged area. Of the 31 species recorded sufficiently frequently for analysis, 19 showed no statistical difference in occurrence between logged and unlogged areas at the power of the study, nine were more prevalent in unlogged areas and three more prevalent in logged areas. Declining woodland birds comprised 22½% of overall species and 33% of those more prevalent in unlogged areas. Mapping of records enabled the response of a subset of species to be examined in greater detail. Four species illustrate the range of responses by declining woodland birds: Eastern Yellow Robin Eopsaltria australis was confined to unlogged areas, White-browed Babbler Pomatostomus superciliosus favoured unlogged areas, Varied Sittella Daphoenositta chrysoptera favoured proximity to unlogged areas and Red-capped Robin Petroica goodenovii was widely distributed in both logged and unlogged areas. The likelihood of recovery of local woodland bird populations is discussed in the context of limited landscape connectivity and the recent colonisation of the remnant by the hyper-aggressive Noisy Miner Manorina melanocephala. White-browed Babbler and Eastern Yellow Robin are considered to be at high risk of local extinction in the remnant.

Cooperative bird discriminates between individuals based purely on their aerial alarm calls

From an evolutionary perspective, the ability to recognize individuals provides great selective advantages, such as avoiding inbreeding depression during breeding. Whilst the capacity to recognize individuals for these types of benefits is well established in social contexts, why this recognition might arise in a potentially deadly alarm-calling context following predator encounters is less obvious. For example, in most avian systems, alarm signals directed toward aerial predators represent higher predation risk and vulnerability than when individuals vocalize toward a terrestrial-based predator. Although selection should favor simple, more effective alarm calls to these dangerous aerial predators, the potential of these signals to nonetheless encode additional information such as caller identity has not received a great deal of attention. We tested for individual discrimination capacity in the aerial alarm vocalizations of the noisy miner (Manorina melanocephala), a highly social honeyeater that has been previously shown to be able to discriminate between the terrestrial alarm signals of individuals. Utilizing habituation–discrimination paradigm testing, we found conclusive evidence of individual discrimination in the aerial alarm calls of noisy miners, which was surprisingly of similar efficiency to their ability to discriminate between less urgent terrestrial alarm signals. Although the mechanism(s) driving this behavior is currently unclear, it most likely occurs as a result of selection favoring individualism among other social calls in the repertoire of this cooperative species. This raises the intriguing possibility that individualistic signatures in vocalizations of social animals might be more widespread than currently appreciated, opening new areas of bioacoustics research.

Do the Calls of a Bird, the Noisy Miner (Manorina melanocephala), Need Adjustment for Efficient Communication in Urban Anthropogenic Noise?

Urban environments are characteristically noisy and this can pose a challenge for animals that communicate acoustically. Although evidence suggests that some birds can make acoustic adjustments that preclude masking of their signals in high-disturbance environments such as cities, studies to date have tended to focus on acoustic signals important in mate attraction (e.g., songs). Far less attention has been given to the impact of urban noise on other kinds of calls. To redress this, we compared a range of different vocalizations (encompassing alarm calls, begging calls and parent response calls) among urban and rural individuals of a successful Australian ‘urban adapter’, the Noisy miner, Manorina melanocephala. We found that urban miners had significantly higher minimum sound frequencies for calls with low base-frequencies (<2 kHz); however, calls with base-frequencies ‘naturally’ above the main frequency range of urban noise (>2 kHz) had the same minimum frequency in urban and rural birds. Dominant frequency and call duration did not differ between urban and rural individuals. Although urban Noisy miners exhibited differences from rural individuals in the minimum frequency of calls, this shift was not large enough to avoid masking from low-frequency, anthropogenic noise. Nevertheless, our findings suggest that the calls of Noisy miners may be naturally well suited to being heard in noisy urban environments by having (a) dominant frequencies higher than low-level, anthropogenic noise and (b) several important call-types with frequencies above the main frequency range associated with urban noise.

Changes in woodland bird communities as replanted woodland matures

Small patches of woodland were progressively established on degraded agricultural land near Gunnedah, northern New South Wales, on the heavily cleared Liverpool Plains. Birds were resurveyed in the plantings, and in agricultural fields (cropping and pasture) and remnant woodland, in 2011–12, 10 years after initial surveys in 2000–01. The plantings in the later survey were 60, 18, 16 and 13 years old, with a shrub layer included in the three youngest cohorts. The survey sites (total 14 ha planted, all within 200 m of remnant woodland) were paired 1-ha plots in each vegetation category. Birds were surveyed by 30-min area searches of each plot eight times over all seasons, using the same plots, procedure and observer as before. In all, 73 species were recorded in the later survey (versus 72 in the earlier survey), for a total of 87 species over both survey periods, with 58 species in 2011–12 (versus 54 in 2000–01) in the plantings; eight of 15 new species visited or colonised the maturing plantings. Avian species richness and abundance increased from the cleared agricultural plots through the progressively older plantings to resemble those in the remnant woodland. Between the first and second surveys, bird communities in the younger plantings converged with those in the older plantings and woodland. The nectar-feeding, foliage-feeding and ground-feeding insectivore guilds benefitted most, having increased in frequency in, or moved into, the younger cohorts of plantings (>13 years old), or both. Several threatened and other declining woodland birds visited, increased in or colonised the plantings. However, noisy miners (Manorina melanocephala) progressively occupied a few plots and excluded some other birds.