What Goes Up, Must Fall Back Down

[This article originally appeared in La Voz, the newsletter of the Friends of Las Vegas National Wildlife Refuge, Vol. 14, No. 3, October, 2016]

I would like to start by apologizing for putting a pun in the title, but I am writing this pre-dawn and I rEGRET nothing. Sorry if that last one flew over your head, it was pretty owlful, but toucan play at puns better than one anyway so if you have anything better please email me! Newton told us why it is when objects go up, they must fall back down. Fall migration is no exception.  September and October is a magical time to be out birding; the hundreds of neo-tropical species that migrate north from the tropics to breed begin to trickle back southward to warmer climates and their wintering grounds. For many species, these wintering grounds are really more of their true home, most spend at least 8 or 9 months of the year in non-breeding areas. These special birds make the perilous trip and leave their habitat behind for the temporary glut of food that comes with Temperate North America’s short summers. Take a Wilson’s Warbler (Cardellina pusilla) for example. These diminutive yellow warblers pass through our area in spring and continue to the misty forests of the Pacific Northwest and Canada to sing their songs, make their nests, and breed. They may have two successful clutches (sets of eggs) over the course of 2 or 3 months, and then the whole family (individually, not like the Griswalds on a road-trip) begin to head back southward. We in Las Vegas usually start experiencing this trickle in late August, and it continues into mid-October. Now an interesting thing to consider is that by breeding, the Wilson’s Warblers have by definition made more of themselves…potentially many more of themselves. Some may be preyed upon en route southward, some will hit windows (see how you can prevent this here), some will be preyed upon by cats (if you like birds, keep your cats indoors!), but still many will successfully make the journey, crossing through our woodlands and safely back to Veracruz, Oaxaca, or Chiapas in Southern Mexico.

Wilson's Warbler in Las Vegas, NM. September, 2013

Every fall when I go out looking for rare eastern migrants I wade through scores of Wilson’s Warblers, potentially dozens on a good day. Cumulatively for the month of September this year I saw, according to my records, approximately 121 Wilson’s Warblers. To give that some perspective I saw 21 in May, I think you get the idea. That excess glut of Wilson's will have to survive the tropical winter in the presence of snakes, tropical species of raptors, even predatory insects. Let your mind run wild with the things that live in the dark jungles of Chiapas or Oaxaca and you get a sense of what these 0.3oz birds will go through before we see them again in May. Anyway, I like fall migration and the physics of neo-tropical birds; what goes up must fall back down.