Urban mixtures of non-essential trace metal elements affect the behaviour and stress levels of a passerine bird in a laboratory experiment.

Trace Metal Elements (TME) are known for their toxicity, which is higher for non-essential TME (nTME) than for essential TME (eTME). However, little is known about the toxicity of eTME and nTME mixtures at concentrations relevant to the urban environment. Since birds are commonly used for biomonitoring, we investigated the behavioural and physiological responses of a passerine model - the zebra finch (Taeniopygia castanotis formerly known as Taeniopygia. guttata) - to TME mixtures in a laboratory setting. Eighty males were divided into 3 exposure groups and 1 control group. Each group was then divided into ad libitum and intermittent feeding groups to better represent challenging natural conditions. The birds were exposed to TME at urban relevant levels via drinking water for 2 months. Three mixtures were tested: one containing only nTME (cadmium, arsenic, lead), one containing the same nTME plus eTME (zinc, copper, nickel), and one containing the same nTME and double the amount of eTME. Our results showed that the more contaminated the birds were with nTME, the less time they spent at the feeders and the more stressed they were. The birds showed an aversion to the mixtures containing TME, particularly eTME. This suggests that birds are able to detect TME in water. Birds exposed to eTME accumulated more copper and less cadmium than the birds exposed only to nTME, highlighting the antagonism between the two types of TME. This study demonstrates that nTME can directly impact the behaviour and stress levels of birds at urban relevant doses.