Assessing pesticides exposure effects on the reproductive performance of a declining aerial insectivore

Abstract

In the context of increasing global environmental changes, it has become progressively important to understand the effects of human activity on wildlife populations. Declines in several avian populations have been observed since the 1970s, especially with respect to many farmland and grassland birds, which also include some aerial insectivores. Changes in farming practices referred to as agricultural intensification coincide with these major avian declines. Among those practices, increased pesticide use is hypothesized to be a key driver of avian population declines as it can lead to both toxicological and trophic effects. While numerous laboratory studies report that birds experience acute and chronic effects upon consuming pesticide treated food, little is known about the effects of the exposure to multiple pesticides on wildlife in natural settings. We monitored the breeding activities of Tree Swallows (Tachycineta bicolor) on 40 farms distributed over a gradient of agricultural intensification in southern Québec, Canada, to evaluate the presence of pesticides in their diet and quantify the exposure effects of those compounds on their reproductive performance between 2013 and 2018. We first assessed the presence of 54 active agents (or derivatives) found in pesticides in 2,081 food boluses (insects) delivered to nestlings by parents and documented their spatial distribution within our study area. Second, we assessed the effect of pesticide exposure through food (number of active agents detected and number of contaminated boluses on a given farm for a given year, while controlling for sampling effort) on clutch size as well as hatching and fledging successes and nestling’s mass upon fledging. Pesticides were ubiquitous in our study system and nearly half (46%) of food boluses were contaminated by at least one active agent. Yet we found no relationship between our proxies of food contamination by pesticides and Tree Swallow reproductive performance. More studies are needed to better understand the putative role of pesticides in the decline of farmland birds and aerial insectivores as potential sublethal effects of pesticides can carry over to later life stages and impact fitness.

Pervasive exposure of wild small mammals to legacy and currently used pesticide mixtures in arable landscapes

“…Moreover, herbivores may be exposed through consumption of vegetation organs, since cultivated and wild plants have been shown to be contaminated by systemic insecticides 49 . Both BRPs and CUPs have been found to accumulate in earthworms, and in insects constituting the boluses of bird nestlings 11 , 65 – 67 . Pesticide overspray can also be an exposure pathway for wildlife, with potential uptake via dermal and respiratory routes but also oral route due to grooming 68 , 69 .…”

Combined influence of food availability and agricultural intensification on a declining aerial insectivore

“…clothianidin, thiacloprid, thiametoxam; Giroux, 2019;Montiel-Le on et al, 2019). Many of those pesticides were also found, even simultaneously, in the insects fed to nestlings by Tree Swallows in our system (Poisson et al, 2021) and may hence have caused lethal and sublethal toxicological effects on nestlings. For instance, many pesticides, such as the neonicotinoids, can alter the neurological, endocrine and immunological systems of non-target animals, including vertebrates, via skin contact, breathing, or food/water consumption (Gibbons et al, 2014;Grue et al, 1997;Lopez-Antia et al, 2015;Mayne et al, 2005;Mineau & Palmer, 2013).…”

“…Furthermore, within heavily cultivated landscapes, the same mechanisms reducing insect abundance, may also impact insectivorous birds, either irrespective of, or in conjunction with, levels of prey. For example, due to the increase of pesticides, insectivorous birds breeding within landscapes dominated by agro‐intensive monocultures may not only be exposed to decreased prey availability, but also to elevated toxicological loads of food items (Malaj et al, 2020; Montiel‐León et al, 2019; Morrissey et al, 2015; Poisson et al, 2021). Breeding within agro‐intensive landscapes may thus have the potential to impact fitness not only through a trophic pathway, via variation in prey availability, but also through other indirect pathways linked to agricultural intensification (Stanton et al, 2018).…”

“…Therefore, increased prey availability should result in greater fitness, including the number of nestlings surviving until fledging, reduced nestling duration (due to increased growth rates), and elevated nestling condition. Our third hypothesis was that Tree Swallow fitness is influenced by agricultural landcover through more than just the overall abundance of food, for example through pesticide exposure (Poisson et al, 2021) or variation in diet quality (Stanton et al, 2018; Twining et al, 2018). We therefore predicted that, after controlling for prey availability, breeding attempts within landscapes occupied by increasing row crops should result in decreased fitness.…”

Negative effects of agricultural intensification on the food provisioning rate of a declining aerial insectivore

“…These agro‐intensive landscapes transition to ones composed primarily of pastures and forage crops (e.g., hay, alfalfa [ Medicago sativa ], and clover [ Trifolium spp.]) in the eastern parts of the study system and are interspersed within large areas of forest cover and a systematic drop in pesticide detections (Poisson et al, 2021).…”