The summer of 2020 was cuckoo in more ways than one . . . both Black- and Yellow-billed! There are two species of cuckoos (Cuculidae) that nest in Maine, Black-billed Cuckoo (pictured above) being more wide-spread while Yellow-billed Cuckoo (pictured below) is scarce with only a few known nesting sites. Both are uncommon, typically only heard in spring when singing, or seen at migrant traps, but the latter half of summer 2020 was
I had an early sense that something was up when every other email or voicemail I got in August was asking “what is this noise?” (answer: one of the cuckoos) or stating “wow, I didn’t know we had cuckoos in Maine!” (answer: we do!). Now, as we dive headfirst into fall, it is fun to look at eBird data and see what an unusual year it was. Note that these charts show the frequency that each species was reported—a percentage of all lists reported that included the species on it. I like using frequency because it isn’t biased by the number of observers (eBird is becoming more popular every year); this makes it better for comparisons with past years than abundance, which is better for comparing with other species, or totals, which is just a big number.
Looking at this chart above, we are comparing the frequency of Yellow-billed Cuckoos reported in 2020 (blue line) with the average over the preceding decade. As mentioned earlier, cuckoos are uncommon in Maine, only being reported on 0.2-0.4% of checklists reported through the summer, though more easily detected as migrants in the fall (seen in mid-September with frequency peaking at 1-1.2% on the decade average). The jumps in 2020 are interesting, with over 1% reported in May and June probably indicating more breeders in the state, and the remarkable late July through mid-Aug window where frequency rose over 1.5%.
The same chart for Black-billed Cuckoos is available below, which shows the spring as being “on par” but a similar spike in the late summer reporting.
It is worth acknowledging flaws of comparing a single year to an average. This would conceal any cyclical events but that doesn’t appear to be the case, at least over this past decade (compare annual Black-billed frequencies here or Yellow-billed here). The best answer to the 2020 spike may be “I don’t know”, but we can think about cuckoo life histories for clues that would produce this event. First, the timing of this is interesting as cuckoos are fairly early nesters and [are believed to] only have one brood in the northeast. This year was apparently challenging for many nesting species (based on opinions of volunteers for the Maine Bird Atlas) but cuckoos seemed to be quite successful, including the first confirmed records (in three different blocks!) for the Maine Bird Atlas (running 2018-2022). Black-billed Cuckoos were also found breeding in 11 new atlas blocks, while they had only been confirmed in 7 blocks during 2018 and 2019. This bump in nesting success is probably thanks to an abundance of food, which in Maine is primarily caterpillars, including: Eastern Tent Caterpillar (Malacosoma americana), Fall Webworm (Hyphantria cunea), Gypsy Moth (Portetria dispar), and Brown-tailed Moth (Euproctis chrysorrhoea)—yes, even the non-natives are food for cuckoos! Interestingly, Yellow-billed Cuckoos have been documented having “reproductive anomalies” during large cicada years, and to our south there was a hatch of “Brood IX” cicadas (which emerge every 17 years), however that didn’t seem to be as large as news outlets made it out to be.
So, perhaps this August peak was from prospecting individuals, fresh off the success earlier in the year. That timing would match up with the more southern populations that do have multiple broods, however there were no reports of any nesting attempts beyond vocalizations during this late period. It is important to note that female cuckoos are also quite vocal, while we think of other “song birds” as having male-dominated songs on the landscape, especially for attracting mates and proclaiming territory, but females have a lot to say too and we are continuously learning more about this.
What we know for sure: Both Yellow-billed and Black-billed cuckoos had very successful nesting seasons in Maine during 2020 and they were especially vocal about it!
Do they actually sound like the clocks?
As a quick primer for cuckoo identification, here are a couple of recordings to compare. The first is a Yellow-billed Cuckoo giving its typical “too – too – too” calls that were commonly heard this late summer. This always reminded me of Speilberg’s velociraptor noises from the Jurassic Park “kitchen scene”.
Compare that to the multi-syllabic calls from Black-billed Cuckoo, often represented as a faster “po-po-po“:
2020 was a great year for cuckoos in Maine, however I think this blog post (and all “good news for birds”) needs to be put in the long term context of the massive declines being documented in bird populations. Both Black-billed and Yellow-billed Cuckoos fit in the “migratory birds” category that has seen a 28% population decline since 1970. If we want to continue to be serenaded by the cuckoo’s call, I recommend following one of these 7 Simple Actions to Help Birds, otherwise, to close on a very out-of-context Kesey quote: “[We’ll] listen to them fade away till all [we can] hear [is our] memory of the sound.”