Indicators of Air Pollution-derived Stress in Birds

Project Highlights:
This is the first project to compare the effects of particulate matter exposure on corticosterone levels in birds in situ.
This study will assess the relationship between identified air pollutants and avian gut microbiome as an indicator of health.
This is a multidisciplinary project using a wide variety of fieldwork and laboratory techniques to investigate different bioindicators of pollution-derived stress in birds.
Overview:
Increased anthropogenic activity (Fig. 1) has led to a large increase in air pollutants1. Some of these substances, even at sub-lethal levels, can have adverse health effects on non-humans, as well as humans2. It is therefore important to find repeatable methods for monitoring pollutant levels in the environment3. Birds are excellent bioindicators as they are ubiquitous and relatively easy to collect observational data from4.

We will test the hypothesis that birds respond to air pollution through changes in their corticosterone levels and gut microbiome. This will allow us to develop trait-based bioindicators too. We refer to air pollution-derived stress as exposure that reduces the Darwinian fitness of an individual`5. Rather than conducting this research in a controlled laboratory environment, we will monitor wild great tits (Parus major) in situ to study exposure to air pollution in situ.

In order to obtain a precise indication of local pollution levels, feathers will be collected from pulli (i.e. ringed young birds that have not left the nest). Blood and faecal samples collected from pulli will also help to identify the localised impacts of air pollution.
Single-particle inductively coupled plasma mass spectrometry (spICP-MS) will be used to investigate the spatial variation of metal contaminants in the feather chemistry of great tit individuals on an urban to rural gradient. We will use spICP-MS and confocal microscopy to separate the compounds into particulate and dissolved forms.

The limited research on birds that has been conducted to monitor air pollution has often been confined to heavy metal elements, with a focus on seabirds7. To the best of our knowledge, no study has attempted to link particulate exposure with corticosterone levels in situ. Another novel element of this research is the use of the bird gut microbiome as an indicator of stress.

Ultimately, this work could identify new indicators of air pollution-derived stress in bioindicators that are widely distributed and move extensively throughout cities. It will also reinforce the use of feathers as a tissue that can be non-invasively sampled to measure air pollution in cities. Both outcomes have positive implications for avian conservation and human health.

Great tit nestboxes will be installed along an urban to rural gradient, using percent green cover to define the gradient. Nestboxes will be placed in close proximity to existing university and council air quality monitoring stations, as these will provide baseline NOx and particulates readings.
We will ring each chick in nestboxes and sample one contour feather. Feathers will be analysed for pollutants using spICP-MS. Confocal microscopy and spICP-MS will enable us to distinguish between particulate and dissolved substances9.
Blood samples will be taken from 3 ringed chicks per brood for corticosterone assessment by radioimmunoassay. A baseline sample will be taken within 3 minutes of handling, followed by a stress-induced sample obtained after 30 minutes10.
Birds will be caught and placed inside bags to collect faecal samples. We will extract DNA from the faecal samples, and use 16S ribosomal rRNA sequencing to identify and compare the bacterial assemblages11.