Since 2016, this species has been assessed as being near-threatened globally (IUCN) and threatened in Canada (SRA) due to its declining populations.

It is qualified as small to medium-sized birds and are estimated to be smaller than American robins, but bigger than sparrows.

The olive-sided flycatcher can be identified by its olive-grey or grey-brownish plumage above and with a white mid-breast section and throat.

They can be distinguished these species by observing the following differences: the plain grey breasts of the greater pewee (as opposed to the vest-like chest of the olive-sided flycatcher), they are twice the weight of the western and eastern wood pewees, and the eastern phoebe has more white underparts than the olive-sided flycatcher.

[2] Olive-sided flycatchers (Contopus cooperi) are part of the class Aves in the order Passeriformes, meaning they are passerines which are known as perching or song birds.

They are part of the family Tyrannidae because they are Tyrant flycatchers found in America and they belong to the genus Contopus which is the Pewee taxon.

Its breeding habitat ranges from California to New Mexico, all the way up to central Alaska, then across Canada (except for most of the Northwest Territories and Nunavut) and through a portion of northeastern US.

This variation appears to be correlated indirectly with the breeding status (single, paired, or feeding young) of the individuals.

The outer part is made with twigs and small branches, while the inside is usually lined with finer material such as grass, lichen, needles, etc.

[15] The Canadian Species at Risk Act lists the olive-sided flycatcher as threatened due to its declining population.

The results suggest that the relative habitat suitability for olive-sided flycatchers in the area of study (Nova Scotia) increased with canopy height and decreased as the habitat moved further away from conifer-dominated forests and areas with dead material which is known to be crucial for their feeding habits.

This species is also expected to prefer valleys, lowlands and flatter areas which have the potential to form wetlands or streams.

The results from this study determined that the forests used in Nova Scotia have a high potential for olive-sided flycatcher populations to be resilient to climate change.

[17] A research made in Eastern Canada showed that disturbances caused by human activities and road proximity have a negative impact on olive-sided flycatcher populations in Canadian national parks.

In their non-breeding habitat, on the east slope of Andres, the winter populations are highly threatened, but the exact threats have not yet been identified.

[9] Burned or freshly-logged forests are great foraging habitats for the olive-sided flycatchers due to the increased presence of flying insects, but they could be negatively affected in these environments by wildfire suppression techniques or salvage logging.