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Near-inertial waves (NIWs) are often an energetic component of the internal wave field on windy continental shelves. The effect of baroclinic geostrophic currents, which introduce both relative vorticity and baroclinicity, on NIWs is not well understood. Relative vorticity affects the resonant frequency feff, while both relative vorticity and baroclinicity modify the minimum wave frequency of freely propagating waves ωmin. On a windy and narrow shelf, we observed wind-forced oscillations that generated NIWs where feff was less than the Coriolis frequency f. If everywhere feff > f then NIWs were generated where ωmin < f and feff was smallest. The background current not only affected the location of generation, but also the NIWs' propagation direction. The estimated NIW energy fluxes show that NIWs propagated predominantly toward the equator because ωmin > f on the continental slope for the entire sample period. In addition to being laterally trapped on the shelf, we observed vertically trapped and intensified NIWs that had a frequency ω within the anomalously low-frequency band (i.e., ωmin < ω < feff), which only exists if the baroclinicity is nonzero. We observed two periods when ωmin < f on the shelf, but the relative vorticity was positive (i.e., feff > f) for one of these periods. The process of NIW propagation remained consistent with the local ωmin, and not feff, emphasizing the importance of baroclinicity on the NIW dynamics. We conclude that windy shelves with baroclinic background currents are likely to have energetic NIWs, but the current and seabed will adjust the spatial distribution and energetics of these NIWs. [ABSTRACT FROM AUTHOR]

Using 18 days of field observations, we investigate the diurnal (D1) frequency wave dynamics on the Tasmanian eastern continental shelf. At this latitude, the D1 frequency is subinertial and separable from the highly energetic near-inertial motion. We use a linear coastal-trapped wave (CTW) solution with the observed background current, stratification, and shelf bathymetry to determine the modal structure of the first three resonant CTWs. We associate the observed D1 velocity with a superimposed mode-zero and mode-one CTW, with mode one dominating mode zero. Both the observed and mode-one D1 velocity was intensified near the thermocline, with stronger velocities occurring when the thermocline stratification was stronger and/or the thermocline was deeper (up to the shelfbreak depth). The CTW modal structure and amplitude varied with the background stratification and alongshore current, with no spring–neap relationship evident for the observed 18 days. Within the surface and bottom Ekman layers on the shelf, the observed velocity phase changed in the cross-shelf and/or vertical directions, inconsistent with an alongshore propagating CTW. In the near-surface and near-bottom regions, the linear CTW solution also did not match the observed velocity, particularly within the bottom Ekman layer. Boundary layer processes were likely causing this observed inconsistency with linear CTW theory. As linear CTW solutions have an idealized representation of boundary dynamics, they should be cautiously applied on the shelf. [ABSTRACT FROM AUTHOR]

Bird damage to commercial crops is a significant problem across the globe, especially for high value crops like wine grapes. Various bird control methods have been developed in the past to reduce bird damage. After a brief review of the current bird damage control strategies, we found the most effective methods, such as netting and hiring a human scarer, rely on intensive manual labour, as well as fragile and costly infrastructure. Whereas the cheaper methods, such as using alarm calls and predator models, are effective for no more than two weeks before the birds habituate to them. We are proposing a novel Unmanned Aerial Vehicle (UAV, more commonly referred to as drone) system incorporating bird psychology for efficient bird damage control. The UAV is equipped with a loud speaker broadcasting distress calls, as well as a crow taxidermy installed on the undercarriage that appears as captured prey. This special UAV configuration is designed to engage birds' well-established abilities to learn to recognise and avoid novel predators, thus providing the benefit that a long-term fear response towards the UAV can be expected. The initial trials were carried out in vineyards around south-eastern Australia. Results indicated the UAV can deter large pest birds such as ravens and cockatoos in a 50-m radius centred on the UAV for an extended period of time. The UAV can also effectively deter small pest birds such as silvereyes for brief time periods after exposure to the UAV. It is also evident from the results that while one UAV is sufficient to protect vineyards smaller than 25 ha, multiple UAVs are needed to protect a large vineyard effectively. • UAV incorporating bird psychology is an effective short-term bird deterring strategy. • The minimum radius of influence of the UAV is 50 m. • Effect of UAV on Silvereyes (Zosterops lateralis) lasts at least 15 min. • A single UAV can protect one vineyard up to 25 ha. • Multiple UAVs are necessary for vineyards larger than 25 ha. [ABSTRACT FROM AUTHOR]