Combined Effects of Hydrological Drought and Reduced Food Availability on the Decline of the Little Penguins in South Australia

Abstract

Droughts in many regions of the world are increasing in frequency and severity which, coupled with effects from anthropogenic water extraction and diversion, are reducing river discharges. Yet to date, few studies have investigated the impacts of hydrological droughts (i.e., reduced river outflows to the ocean) on seabirds. Here, we examined the consequences of the “Millennium Drought” on the local decline of an iconic Australian seabird, the little penguin (Eudyptula minor). We analysed monthly and annual penguin numbers in relation to river outflow, rainfall, the characteristics of the coastal waters (sea surface temperatures and chlorophyll-a concentrations), and local abundance of key predators and prey species. We found a negative association between monthly penguin numbers and both sea surface temperatures and river outflow. Annual penguin numbers were positively associated with southern garfish numbers (our local indicator of food availability) but negatively associated with annual chlorophyll-a concentrations. Our findings emphasizing the need for further research into the effect of hydrological droughts on seabird populations and for improved river management that account for potential downstream impacts on the coastal environment receiving freshwater from rivers.

Human activities at night negatively impact Little Penguin (Eudyptula minor) numbers and behaviours

“…2007, Colombelli‐Négrel 2015, Colombelli‐Négrel & Tomo 2017, Johnson & Colombelli‐Négrel 2021, Colombelli‐Négrel et al . 2022), such as the Granite Island population.…”

“…In addition, when animals are continuously exposed to stressful factors, they can enter a chronic state of stress (Cyr & Romero 2007), which can lead to stress-related diseases (Mortimer & Lill 2007), alter or disrupt their behaviours (Burger & Gochfeld 1993, Angelier et al 2008, or impact their fitness (Mcclung et al 2004, Lupien et al 2009. Combined with other pressures from their environment, regular human disturbances could therefore have serious consequences for the long-term survival of a population, especially for those that already experience a high number of other threats (Bool et al 2007, Colombelli-N egrel 2015, Colombelli-N egrel & Tomo 2017, Johnson & Colombelli-N egrel 2021, Colombelli-N egrel et al 2022, such as the Granite Island population.…”

“…Although globally classified as 'Least Concern' (BirdLife International 2020), Little Penguin population declines up to 80% have been recorded in South Australia over the past two decades (Wiebkin 2011, DEWNR 2016. Multiple factors are believed to be responsible for these declines, including predation on land and at sea, starvation and climate change (Wiebkin 2011, DEWNR 2016, Colombelli-N egrel & Tomo 2017, Johnson & Colombelli-N egrel 2021, Colombelli-N egrel et al 2022. Assessing human disturbance on wildlife is especially critical for declining populations that are already under threat from a variety of factors (Bell et al 2020), such as in the case for Little Penguins in South Australia.…”

“…Multiple factors are believed to be responsible for these declines, including predation on land and at sea, starvation and climate change (Wiebkin 2011, DEWNR 2016, Colombelli‐Négrel & Tomo 2017, Johnson & Colombelli‐Négrel 2021, Colombelli‐Négrel et al . 2022). Assessing human disturbance on wildlife is especially critical for declining populations that are already under threat from a variety of factors (Bell et al .…”

“…variation in marine temperatures and wind speeds; Johnson & Colombelli‐Négrel 2021) and low food availability, probably due to reduced river outflow to the ocean from the Murray Mouth (Colombelli‐Négrel et al . 2022). Since its decline, the colony has experienced an increase in human activities at night from fewer than 2% of the monitored nights before 2016 to more than 23% of the monitored nights in 2018 (Colombelli‐Négrel 2019).…”