Petrochelidons revisited (why is New Mexico so darn high?)

I'll start off by saying the Cliff and Cave Swallows (P. pyrrhonota and P. fulva respectively) that were the focus of my previous post certainly weren't paying attention, as I discovered this morning (Mar. 5).
While driving over the Calle del Norte bridge en route to Mesilla Valley Bosque SP, I noticed several swallows flying around the bridge. This is a popular spot for nesting P. pyrrhonota in the summer, so I stopped and checked to see if maybe the P. fulva (which was what I had assumed the identity of these birds was given the date) were inspecting potential nest site. This would be especially interesting as I do not believe P. fulva have been noted as nesting at this location before. After looking at the flock of approximately a dozen swallows, I was instantly taken aback. Several had very pale, cream colored foreheads. The collars also looked wrong for P. fulva. I also happened to hear one call and it was giving the harsh "chew" I am used to hearing from P. pyrrhonota when I happen to disturb a nesting colony (I have read it is an alarm call). I also heard a few of the birds present give the "phew" call that is characteristic of P. fulva. Having heard both calls, I was suspicious that some individuals were probably P. pyrrhonota. I took quite a few photos (most of which were useless) and I went on with my morning's birding.
Upon inspecting my photos, I realized that my suspicions in the field were confirmed. At least 3 of the Petrochelidon swallows hanging around the bridge were in fact P. pyrrhonota. If it were April or May, this wouldn't have bothered me, but the fact that its only March (and early March at that) is note-worthy.

A poor photo of P. pyrrhonota Notice the pale forehead and dark throat 

Calle del Norte Bridge, Dona Ana County, NM

Mar.5, 2017

  Looking at the reports of P. pyrrhonota so far this year in the US, it is worth noting that there are quite a few reports west of NM in Arizona and California. However, remember back to mid-February when I posted the occurrence map for P. pyrrhonota then, there were already quite a few reports. What has changed significantly in the past 14 days has been the influx of P. pyrrhonota into Texas and the increase in individuals detected in Arizona and California.

Reports for P. pyrrhonota for 2017 in the US as of Mar. 5, 2017 (eBird)

The thing that immediately strikes me when I look at this map is that there are a quite a few reports of P. pyrrhonota at higher latitudes than Las Cruces, NM already in adjacent states. So why should these arrivals in New Mexico be unusual?
There is a topological quirk that separates NM from Arizona and Texas that is both a blessing and the bane of New Mexico birding for listers. New Mexico's mean elevation is 5,700 feet (approx. 1737 m) which is the 4th highest in the United States. Compare this to Arizona and Texas which have mean elevations of 4,100 ft (approx. 1250m) and 1,700ft (approx. 518m) respectively. This is likely a contributing factor as to why Black Vulture (Coragyps atratus) and Crested Caracara (Caracara cheriway) (to name a few species) are so seldom encountered in New Mexico as compared to Arizona and Texas where there are well established populations. Elevation and topography also influence rainfall and subsequently have an affect on the vegetation structure in many areas, particularly the desert in the southern portion of the state.
One example of this can be seen in the breeding range of Lucy's Warbler (Oreothlypis luciae) in New Mexico compared to Arizona.

Reports for Lucy's Warbler (Oreothlypis luciae) from May-Jul (eBird)

O. luciae is relatively unique among Wood-Warblers (Parulidae) in that it is a cavity nester (the only other being Prothonotary Warbler (Protonotaria citrea)). This means that the diameter of vegetation is a potential limiting factor in its breeding range. It is fairly widespread throughout Arizona in lower elevation areas, but in New Mexico it is mostly restricted to riparian areas (the Rio Grande and Gila River). This is likely owing to the fact that there is little vegetation of an appropriate diameter away from reliable water sources, especially in the particularly parched Chihuahuan desert.

So what does this have to do with P. pyrrhonota? Well, though they have apparently already arrived in adjacent states, it is important to note that the timing of arrivals in New Mexico is often later than that of neighboring states. Even so, with the mild winter, perhaps it makes sense that a few P. pyrrhonota have decided to push northward and upward into New Mexico early this year.
I am going to go out on a limb here and predict that this year (as is the case most years recently, it seems) will be characterized by firsts in terms of northward expansion of species. Not necessarily crazy neotropical first records, though the Black-backed Oriole in PA is certainly an interesting one. Rather, I imagine more regular species will continue to extend the fringes of their ranges northward in an expansion that will be measured in tens of miles rather than hundreds. But even so, over time this will make a difference. And some species, like the Tufted Flycatcher (Mitrephanes phaeocercus) may continue its apparent expansion into the US in the Huachuca Mtns. Now that young have been produced from the "traditional" nest site, perhaps its time to search for more pairs. And of course those of us who were unable to see the 1st accepted U.S. record Pine Flycatcher, we are holding our breath in anticipation to see if it returns this May.
If the untimely occurrences thus far this year are any indication, this is going to be an interesting year...

P. pyrrhonota

Note the pale (slightly buffy in this shot) forehead and extensive dark coloration on the throat and rufousy collar

Calle del Norte bridge, Dona Ana County, NM

Mar. 5, 2017