News & Features

Decline of the Bullbat, ABA Bird of the Year

Male Common Nighthawk in Flight by Alex Lamoreaux

With their loud “peeent” calls, erratic flight, and “booming” courtship flight, Common Nighthawks can put on quite a show.    One of our declining aerial insectivores, the Common Nighthawk has been attracting a lot more attention in recent years.   The American Birding Association has named the Common Nighthawk as its “Bird of the Year” for 2013. The Common Nighthawk certainly is a misnamed bird — not a hawk but a Caprimulgid, not nocturnal but crepuscular, and not as common as it used to be. A colloquial name of “bullbat” has been used to describe its bat-like flight. The Common Nighthawk has declined so much in Pennsylvania that it now is considered “Near Threatened” by the Ornithological Technical Committee of the PA Biological Survey.  This status change was based on declines recorded from the 1st Pennsylvania Breeding Bird Atlas to the 2nd PBBA.  For decades, state birders have witnessed the declines of nighthawks on breeding grounds and in migration. These declines have been even more dramatic in Canada where the species now is considered nationally Threatened. Pennsylvania also has witnessed a dramatically declining passage migration of the “bullbat.”

ABA 2013 Bird of the Year Badge

ABA 2013 Bird of the Year Badge

Common Nighthawks are birds of the air. They feed almost exclusively on insects, catching them while on the wing. They often nest and feed in urban environments, taking advantage of the lights in towns that attract insects. They also tend to nest on flat roofs, graveled areas, and open cultivated fields near humans. Nighthawks also nest in wilder areas away from towns on rocky outcrops including talus, cliffs, burned areas, and reclaimed strip mines.  They do not make a nest, but rather scrape out a depression in gravel, leaf litter, slag, cinders, railroad grades, or bare rock and soil. Nighthawks perch parallel to their support branch so even when they roost in trees they can blend in rather well. Their urban nesting habits have made them vulnerable to changes in roofing materials and to increases in nest predators such as crows, feral cats, and raccoons. The change to rubberized roofing materials is not as suitable for them as the gravel surfaces used in years past. In forested landscapes, nighthawks use burned-over areas, so the lack of controlled burns may be contributing to a decreased potential nesting areas. There also are suspicions that the use of pesticides, especially on the wintering grounds of South America and perhaps throughout their range, may be contributing to the species’ decline.

Perched Common Nighthawk by Alex Lamoreaux

Perched Common Nighthawk by Alex Lamoreaux

 The best evidence for a decline in the nesting population in Pennsylvania comes from the PA Breeding Bird Atlases (PBBA). There was a -71% decline in the number of blocks reported from the 1st PBBA to the 2nd PBBA (from 754 blocks in the 1st PBBA to 219 in the 2nd) (Grove 2013).  The decline in confirmed blocks was even more extreme, dropping from 62 to only 10 blocks.  Since nighthawks are found in urban areas where there are many birders, and they are easily seen and identified, these changes are strong evidence of a precipitous decline. Since the 1st PBBA, the Common Nighthawk has disappeared as a breeding species from most of the northern tier — from Potter County across to Wayne County. There are some concentrations of nighthawk reports in the Pittsburgh area, the Wyoming Valley in the upper Susquehanna River region, the Lehigh Valley, and a cluster north and west of State College in Clearfield and Clinton Counties that suggest the use of reclaimed strip mines there. The records in remote strip mine areas suggest that some nesting populations may remain poorly surveyed by any project. The nighthawk has disappeared from many locations where it was found previously including many smaller towns and cities where flat roofs hosted nesting birds. The Common Nighthawk already was declining by the time of the 1st PBBA in 1983-89 (Brauning 1992).   

 Atlas results may be a better indicator of changes in crepuscular species than the Breeding Bird Survey, but the BBS surveys are done annually so they are of interest. They echo the message sent by the Atlas data.  The Breeding Bird Survey data shows a non-significant decline of -4.5% annually (Sauer et al. 2012), but nighthawks are not well represented by BBS routes because of their crepuscular behavior and because urban areas and remote rocky areas are not well surveyed by BBS routes. The continental population has declined 2.2% per year, 1966-2011 (Sauer et al. 2012).

 It is well-known that the change in materials used for flat roofs has probably contributed to nighthawk nesting opportunities in urban settings. I would add that many Pennsylvania towns have lost the small factories such as in the textile industry —- so those flat roofs that nighthawks nested on have greatly declined or disappeared from some communities. It also has been speculated that crow populations have invaded urban areas and contributed to nest failures of nighthawks.  Use of pesticides on both the breeding and wintering grounds also are possible contributing factors to declining dietary options for this aerial insectivore.  

On the other side of the issue, various sources point to the Common Nighthawk’s use of non-urban habitats including talus slopes, cliffs, reclaimed strip mines, railroad beds, and possibly scrub barrens/burned-over areas. During the statewide Northern Saw-whet Owl survey (2000 – 2001) some observers found nighthawks flying over pretty old strips in Clinton County and other rural locations that cannot be explained by flat roofs. Reclaimed strip mines may be unappreciated breeding grounds in Pennsylvania. Atlas records have teasingly suggested that there are more nighthawks out there in the recovering strip mine areas. Birders have reported nighthawks flying over PA’s “Grand Canyon” in the North central region of the state where there are no flat roofs but some cliffs, talus, and rim rock along Pine Creek canyon.  Nighthawks have nested on the rocks at the Lehigh Gap Nature Center on a reclaimed, denuded (zinc pollution) mountainside near Slatington, Lehigh/Carbon counties.  

Some PA birders stage nighthawk watches and post their observations. Hawk watches, especially Jacks Mountain, are favorite places to observe the fall nighthawk migration. So, the birding community is quite aware of nighthawk declines. Nighthawks continue migrating south through North America, through Middle America into South America where they spend the winter. The wintering range is poorly understood, but the limited records suggest that few Common Nighthawks spend the winter in northern South America and continue south into southern Brazil. Paraguay, Uruguay, Argentina, and parts of bordering countries.  As such, the Common Nighthawk has one of the longest migrations of any land bird.  They are gregarious in migration, forming large flocks.  These flocks dramatically pass through Central America lowlands where flying insects are abundant during the rainy season there.  Hundreds may pass through places like the Canal Zone of Panama in a few minutes. 

Flying Female Common Nighthawk by Alex Lamoreaux

Flying Female Common Nighthawk by Alex Lamoreaux

The decline of Common Nighthawk is part of a widespread decline of aerial insectivores. Chimney Swifts and many swallows and martins also have suffered losses in recent years. Even the ubiquitous Barn Swallow has declined dramatically.The “bullbat” population may be a barometer for the health of the atmospheric arthropod community.   

On a personal note, one of the authors (Doug) has witnessed this nighthawk decline personally in Columbia County. When I was a kid, I watched dozens fly around overhead in Bloomsburg, a mill town along the Susquehanna River, while listening to a ball game on the radio with my Dad in the summer evenings. It was a sight that made a strong impression on me, one of the reasons for a lifetime interest in birds  I returned to the old neighborhood several times during the 2nd PBBA and failed to see or hear a nighthawk despite the many flat roofs on local factories, stores, and the university. They’re gone! The community is poorer for it.

By Doug Gross, PA Game Commission

Thanks to Alex Lamoreaux for use of his photographs. 

 

 

Sources for this Story and for more Information about Common Nighthawks:

 American Birding Association website. Bird of the Year:   Common Nighthawk. http://aba.org/boy/

Brauning, D. W. 1992. Common Nighthawk (Chordeiles minor). Pages 168-169 in D. W. Brauning, editor. Atlas of breeding birds in Pennsylvania. University of Pittsburgh Press, Pittsburgh, PA.

Brigham, R. M., Janet Ng, R. G. Poulin and S. D. Grindal. 2011. Common Nighthawk (Chordeiles minor), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu.bnaproxy.birds.cornell.edu/bna/species/213

Goguin, C. B. 2010. Common Nighthawk (Chordeiles minor), pages 267 – 270, In Terrestrial Vertebrates of Pennsylvania, A Complete Guide to Species of Special Concern (M. A. Steele, M. C. Brittingham, T. J. Maret, and J. F. Merritt, eds.). The Johns Hopkins University Press, Baltimore, MD.

Grove, G.   2013. Common Nighthawk (Chordeiles minor), Pages 2016 – 217, In 2nd Atlas of Breeding Birds in Pennsylvania (A. M. Wilson, D. W. Brauning, R. S. Mulvihill, Eds.), The Pennsylvania State University Press, University Park, PA.   

McCracken, J. 2008.   Are aerial insectivores being bugged out?   BirdWatch Canada 42:4-7.

McWilliams, G. M., and D. W. Brauning. 2000. The Birds of Pennsylvania. Comstock Publishing Associates, Ithaca, NY.   

Nebel, S., A. Mills, J. D. McCracken, and P. D. Taylor. 2010. Declines of aerial insectivores in NorthAmerica follow a geographic gradient. Avian Conservation and Ecology – Écologie et conservation des oiseaux 5(2): 1. [online] URL: http://www.ace-eco.org/vol5/iss2/art1/

Sauer, J. R., J. E. Hines, J. E. Fallon, K. L. Pardieck, D. J. Ziolkowski, Jr., and W. A. Link. 2012. The North American Breeding Bird Survey, Results and Analysis 1966 – 2011. Version 07.03.2013 USGS Patuxent Wildlife Research Center, Laurel, MD.