The Changing Birds of New Mexico

New Mexico is warming up and its avifauna is responding. Some consequences of warming will be predictable; for example, species will tend to shift their ranges northward and breed earlier in spring. But shifting species will encounter new predators, parasites, and competitors, the effects of which will be unpredictable. Furthermore, even species that live in the same places can vary in sensitivity to heat, drought, and habitat changes.

‘Black hawk and the white-winged dove’ is a mournful lyric from an Emmylou Harris song, but also a reminder of the large set of bird species that are expanding their ranges in New Mexico. Sandy Williams, Research Associate at UNM’s Museum of Southwestern Biology (MSB), reports that at least 50 bird species have expanded their breeding ranges within New Mexico, with northward and westward expansions being most common. In addition to the Common Black-Hawk and White-winged Dove mentioned by Harris, a suite of warm-climate species have expanded northward over the couple of centuries since the ‘Little Ice Age’. These expanding species include Greater Roadrunner, Curve-billed Thrasher, Cactus Wren, and Lucy’s Warbler, each of which reaches its northern limits in (or near) New Mexico. Williams is working on a book on the birds of New Mexico that will describe these and other historical changes. There are fewer species whose ranges have shrunk in New Mexico over the same time period, but Williams points out that declines are harder to detect. In the Albuquerque area, species that have clearly declined over recent decades include Yellow Warbler, Lewis’ Woodpecker, and Yellow-billed Cuckoo (1).

Two species that could be vulnerable to climate warming in New Mexico: Mexican Spotted Owl (left) and Northern Goshawk (right), represented by specimens at the Museum of Southwestern Biology of the University of New Mexico. These series of salvaged specimens, accumulated over decades, provide irreplaceable documentation of these populations, their genetics, diet, and other characteristics.

There are many breeding bird species whose southern range limits are in New Mexico. These include three sage specialists — Sage Thrasher, Sagebrush Sparrow, and Sage Grouse (the latter species was extirpated during the 20th century) — and many montane forest species, including Gray Jay, American Three-toed Woodpecker, Dusky Grouse, Pine Grosbeak, Clark’s Nutcracker, ruby-crowned and golden-crowned kinglets, White-crowned Sparrow, Wilson’s Snipe, and Boreal Owl. As temperatures warm, we predict that these species will contract their ranges or withdraw from New Mexico. Montane forest species are typically restricted to above ~7000 ft and are predicted to shift toward mountain peaks, a phenomenon known as the ‘escalator to extinction’. This is even likely to affect species that are currently abundant, such as Dark-eyed Junco and Flammulated Owl.

Disappearance of New Mexico’s forests would sharply reduce bird diversity. A study of ponderosa and piñon pines recently showed that warming temperatures accelerate tree death during drought, adding to the evidence that New Mexico’s forests have no long-term future (2). As forests decline, top predators such as Northern Goshawks and Mexican Spotted Owls would likely be among the first species to disappear. Pinecone predators like the Red Crossbill are abundant and closely dependent on pine forests, but a study of Old World crossbill species showed how these birds could disappear even sooner than the pine trees due to a phenomenon called ‘phenological mismatch’ (3). In short, earlier opening of pinecones in spring is predicted to lead to a period of food scarcity for crossbills in late summer. Such shifts in timing, or ‘phenology’, are happening everywhere. For example, a study of California species showed that they are nesting one week earlier, on average, than a century ago; this might allow species to track their preferred temperature for nesting, even without shifting their geographic ranges (4).

Climate change doesn’t just cause population fluctuations and range shifts, it also is likely to cause evolution that is rapid enough to be measured over years or decades. I don’t yet know of examples of ‘real-time’ adaptation in New Mexico birds, but examples elsewhere suggest that it’s happening here too. For example, a recent study of Great Tits in Britain showed that their beaks have gotten larger over a few decades in order to better exploit bird feeders, and their genome sequences revealed exactly which beak-enlarging genes had been favored by natural selection (5). Natural selection on birds must also be occurring in New Mexico towns and cities where we have created thriving ‘bird-seed economies’. In fact, House Finches in urban Tucson, Arizona, have larger beaks than neighboring populations that eat native plant seeds, mostly likely because the urban birds have adapted to eating thick-hulled sunflower seeds (6). And the latest study on rapid bird beak evolution showed that Florida Snail Kites have adapted to eat a large invasive snail species by an increase in their beak sizes that occurred over less than two generations (7).

Body size and plumage color are also expected to evolve in response to a warming climate. In the eastern U.S., measurements of banded birds showed that several species are getting smaller due to warming (8). In southwestern Arizona, museum specimens revealed that Horned Larks have evolved darker back coloration as an adaptation for background matching in response to agriculture, which has darkened the color of the soil (9). Tests for historical changes in traits of New Mexico birds would be timely and, fortunately, UNM has one of the best and fastest growing bird-specimen collections with which to conduct these studies.

Another way that warming will affect birds is by affecting their parasites, diseases, and disease vectors, many of which have yet to even be discovered. Researchers at UNM Ornithology are surveying the malaria-related parasites of birds in New Mexico pine forests and have found that approximately two-thirds of infections represent previously unknown parasite species (10). In New Mexico on the whole, there are likely to be hundreds of malaria-related parasite species, and each has the potential to harm susceptible bird populations if distributions shift in response to warming.

In summary, many environmental changes are affecting New Mexico’s birds, and changes are occurring with shocking speed. Scientists and citizen-scientists will need to work fast to detect these changes in real time.

  1. J. S. Findley, Birds in Corrales. Occasional Papers of the Museum of Southwestern Biology (2013).
  2. H. D. Adams et al., Temperature response surfaces for mortality risk of tree species with future drought. Environmental Research Letters. 12 (2017), doi:10.1088/1748-9326/aa93be.
  3. E. T. Mezquida, J.-C. Svenning, R. W. Summers, C. W. Benkman, Higher spring temperatures increase food scarcity and limit the current and future distributions of crossbills. Diversity Distrib. 16, 743 (2017).
  4. J. B. Socolar, P. N. Epanchin, S. R. Beissinger, M. W. Tingley, Phenological shifts conserve thermal niches in North American birds and reshape expectations for climate-driven range shifts. Proc. Natl. Acad. Sci. U.S.A. 114, 12976–12981 (2017).
  5. M. Bosse et al., Recent natural selection causes adaptive evolution of an avian polygenic trait. Science. 358, 365–368 (2017).
  6. A. V. Badyaev, R. L. Young, K. P. Oh, C. Addison, Evolution on a local scale: Developmental, functional, and genetic bases of divergence in bill form and associated changes in song structure between adjacent habitats. Evolution. 62, 1951–1964 (2008).
  7. C. E. Cattau, R. J. Fletcher, R. T. Kimball, C. W. Miller, W. M. Kitchens, Rapid morphological change of a top predator with the invasion of a novel prey. Nat Ecol Evol. 21, 1 (2017).
  8. J. Van Buskirk, R. S. Mulvihill, R. C. Leberman, Declining body sizes in North American birds associated with climate change. Oikos. 119, 1047–1055 (2010).
  9. N. A. Mason, P. Unitt, Rapid phenotypic change in a native bird population following conversion of the Colorado Desert to agriculture. Journal of Avian Biology (2017), doi:10.1111/jav.01507.
  10. R. A. Marroquin-Flores et al., Diversity, abundance, and host relationships of avian malaria and related haemosporidians in New Mexico pine forests. PeerJ. 5, e3700 (2017).

Reprinted from Bosque Tracks, Winter 2018 issue.


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