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When entering the Emerald Island entrance on Market Street, I've noticed the rather unique trees overhead and the extremely loud birds there. In fact, the racket is so loud, I'd always assumed the bird sounds were recorded (perhaps to keep rodents away). When looking up, however, I noticed the birds were very real and in very large numbers. Needless to say, I've never noticed this on Fremont Street, the Strip, or the plethora of locals casinos and strip malls that populate the valley. BTW, the birds were squawking at sunset (I'm sure they do the same at sunrise). They were silent at night... So what are these trees and what kind of birds are they? I have no idea on the trees, but my very uneducated guess is that the bird are mynahs. Am I in the ballpark?
Based on our limited arboreal knowledge, we believe the trees lining the sidewalk outside Emerald Island on Market Street in downtown Henderson are chitalpas or catalpas (Chitalpa tashkentensis). They're known for their slender trunks and canopy, suitable for the narrow urban sidewalk environment, plus willow-like leaves, and white or pinkish flowers during the summer months. These trees are specifically chosen for their resilience to the hot arid climate of southern Nevada. In fact, we believe the variety on Market Street are chilopsis trees, also known as desert willow for their willow-like flowers; they're also members of the catalpa family and native to southern Nevada.
As for the birds, they're definitely not mynahs, though your description of loud squawking birds does sound like them. Common mynas (Acridotheres tristis) are known for exactly that: very vocal raucous calls often described as squawks, chatter, and harsh, especially in groups, and they thrive in urban/suburban settings with trees near buildings or parking areas.
However, common mynas are decidedly not established in the Las Vegas/Henderson area, or anywhere in Nevada, or anywhere in the Southwest for that matter. Feral populations in the mainland U.S. are limited primarily to southern Florida.
Rather than mynahs, the behavior and location (noisy flocks in urban trees near buildings/parking areas in downtown Henderson) strongly point to great-tailed grackles (Quiscalus mexicanus). They're extremely common in the Las Vegas/Henderson metro, including parking lots, streets, and treed areas. They're also incredibly loud and vocal, with a huge repertoire of calls: harsh squawks, rattles, mechanical squeaks, whistles, croaks, and "alien" or "electrical malfunction" sounds — often described as squawking or raucous.
They're highly social, so they gathers in flocks (sometimes large) that roost in trees and get especially noisy at dawn (when waking up, claiming territory, or coordinating) and dusk (when settling into roosts). They're quite active during daylight hours, but silent at night once roosted.