Following the Western Monarch Decline


Image courtesy of USFWS Pacific Southwest Region

While the role bees and hummingbirds play in our ecosystems is well documented and widely renowned; a large amount of pollination across North America is also conducted by other insects like flies, beetles, ants and butterflies. One of our most recognizable butterfly species is the Monarch, which has two main migratory populations: the Eastern and Western Monarchs. These butterflies are known for their remarkable migration patterns (some groups make trips of up to 3,000 miles) and for their striking orange, black and white wing colouring. While less efficient in pollination than their specialized bee counterparts; Monarch butterflies are some of the most widespread insect pollinators on the continent and also act as a keystone species: should they disappear from the ecosystem, the ecosystem will be irreparably changed.

Population counts conducted by the Xerces Society For Invertebrate Conservation have found that the Western Monarch’s count estimates that only around 29,000 remain as of 2020. Worryingly, this is the second year in a row the total population amount has fallen below the estimated critical migration threshold. Even as researchers anticipated a slight resurgence of the population, the Xerces Society’s findings have indicated that there is “no meaningful difference between Western Monarch population of [2019-2020] and [2018-2019]”. Most unfortunate is that scientists and activist groups alike have been sounding the alarm on this slow-motion trainwreck for almost 40 years, back when the Western Monarch population was estimated to be around 4.5 million!

The reason behind this precipitous decline is because of the limited legal (de jure) and actual (de facto) protection of either the butterfly population itself or the many overwintering sites along the California coast that the species have migrated to and from for thousands of years. The Xerces Society counts that at least 20 active overwintering butterfly breeding sites have been significantly impacted or outright destroyed by human actions in just the past 5 years alone. Sadly, this is on top of 20 more locations that have been lost since 1990. Many of the trees that the butterfly population rely on have been chopped down to make way for private development, but more alarmingly, many other trees on public lands and in de jure conservation spaces.

Another explanation for why the butterfly population has dwindled to such an extent is greater habitat degradation across the continent’s alpine meadows, prairies and plains; where wildflower fields have been largely replaced by soy and corn farms, or simply lost to invasive grasses. The adults of the species are largely sustained by the nectar gathered from wildflowers from across the Western US and Canada, stopping and gathering sugars from these flowers to use as energy to survive their migration. After the long migration is complete, the butterflies reproduce and their larvae feed on local milkweed plants in California. This delicate cycle has been sustained up until the modern era, when industrial fertilizers and pesticide use were introduced to the system. The fertilizers favoured non-native and sometimes invasive species over the milkweed and other early-flowering endemic bushes, while the pesticides actively harmed the butterflies at every stage of their lifecycle.

On a larger scale, climate change has begun to have a severe impact on the ability of Western Monarch groups to adequately react to seasonal and temperature changes. Their migration is highly linked to the shift from winter to spring and the blooming of the wildflowers that will sustain their long journey. With climate change inducing more volatile weather changes, sometimes on a day-to-day basis (similar to how Denver has temperatures over 90F and then two days later saw snow this September). Moreover, climate change has increased the frequency and severity of droughts and other extreme weather phenomena across the North American West, meaning that these butterflies have been far less likely to survive the overwintering period and even make into the breeding season. The combination of these effects has led to the death of literally hundreds of millions of butterflies over the past couple decades.

In order to help stop the extinction of these essential pollinating insects, it’s important we first press our legislators to take the conservation of our public lands seriously! It’s a direct result of state and federal mismanagement of our natural spaces that this resplendent species may see extinction before 2050. So that we can safeguard the Western Monarch, we as ordinary Californians can and should plant as many native varieties of milkweed if possible, and if not, write messages to your county and state representatives to urge them to think about the Western Monarch’s role as a keystone species.


Written by — Josh Kalia

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