Sensitivity of High Conservation Value Birds to Para-Aminopropiophenone (PAPP) Determined by Sub-Lethal Dose–Response Assay

Abstract

Para-aminopropiophenone (PAPP) is a methaemoglobin (MetHb) forming compound used for the lethal control of invasive carnivores and mustelids. By measuring the dose-dependent inhibition of O2 transport arising from the oxidation of haemoglobin (HbFe2+) to MetHb (HbFe3+), we determined the sensitivity of nine bird species to PAPP. A methaemoglobinaemia absorbance index (MAI) was validated in five common bird species to determine thresholds associated with a 99% probability of survival (ST99) and a 50% probability of mortality (LT50). Dose–response trials in high conservation value birds sought MAI values below the ST99 threshold, projecting the LT50 value and avoiding the need for lethal outcomes. Black-backed gull (LT50 = 1784.7) and eastern rosella (LT50 = 1074 mg kg−1) were the most tolerant species, while brown kiwi (LT50 = 8.4 mg kg−1) and weka (LT50 = 9.3 mg kg−1) were the most sensitive. Takahē were of intermediate acute sensitivity (LT50 = 51 mg kg−1), although protracted impacts on haemoglobin were observed in takahē up to 72 h later and associated with PAPP doses as low as 25.6 mg kg−1. In pukeko (LT50 = 138.4 mg kg−1), protracted declines in haemoglobin 72 h later occurred at doses as low as 29.5 mg kg−1, while at higher doses (253 and 112 mg kg−1), deaths resulted after 4–6 days. Based upon PAPP doses that caused acute and protracted responses, we provide estimates for the lowest observable adverse effect level (LOAEL) and no observable effects level (NOEL) for nine bird species.