Creature Feature: Whooping Cranes

The whooping crane (Grus americana) is the perfect representative for both World Migratory Bird Day (This past Saturday, May 9th) and Endangered Species Day (This Friday, May 15th). Whooping crane populations were almost reduced to the point of extinction by 1941. Although populations have rebounded since that point, with less than 1,000 whooping cranes alive today, much work still needs to be done [1].

An adult whooping crane sporting the distinctive dark red crown and chick [Source: International Crane Foundation]

As the tallest bird species in North America, the whooping crane is difficult to miss (if you’re lucky enough to see one of the few). Snowy white, with black wing tips and a dark red crown that extends to the bill, this bird would be an imposing figure to see flying overhead – and they fly long distances. From March to April, birds from two wintering grounds near the Texas Gulf Coast depart for breeding grounds further north and often arrive beginning in late April. Experienced breeders tend to reach their breeding destination first. Younger birds begin to leave the breeding grounds for the wintering grounds in mid-September. Families and breeding pairs then leave in early October. Birds generally arrive back at wintering grounds in late October to early November, but there are some stragglers who arrive later. Birds frequently stop to forage and rest during migration.

At the breeding and wintering grounds and along these migratory routes, whooping cranes can experience many human-induced threats. In the past, hunting, habitat degradation, and human-introduced contaminants have greatly reduced populations and contributed to the whooping crane gaining endangered status from the IUCN. Now, research shows that power-line collisions, continued habitat destruction, and other human disturbances are negatively affecting whooping cranes [2, 3].

A range map for Whooping cranes. The birds breed at their summer grounds in the northern North America (shown in blue). Cranes fly along the red trajectory to reach their wintering grounds along the Gulf Coast (see orange areas in Texas and Florida). [Source]

In order to conserve the whooping cranes, scientists have used both in situ (on-site in the wild) and ex situ (captive) efforts. In 1984, an early in situ program began removing eggs from whooping crane nests that were not likely to develop properly. The eggs were replaced with fertilized eggs from other nests to increase hatching success. While whooping cranes normally lay two eggs, one hatchling often dies from siblicide (the younger sibling usually killed by the older) or predation. Thus, spreading out the fertilized eggs among nests may lead to increased chick success. During the study period, many pairs were successful at rearing single eggs, and overall hatching success increased. Some eggs were also removed to establish captive breeding populations [2, 4, 5] in ex situ conservation programs. The goal of many ex situ conservation programs is to breed animals in captivity to release into the wild.  Those released animals must be raised by someone, and without captive whooping cranes, scientists turned to the more common sandhill crane (Grus canadensis) [6]. The sandhill cranes fostered the whooping crane offspring in captivity, but the offspring struggled to thrive when they were released to the wild. The whooping cranes may have sexually imprinted on their sandhill crane foster parents (meaning that they learned to desire characteristics from the other species), making it difficult for them to pair up with other whooping cranes to breed [2]. Infertility, low egg counts, and delayed onset of egg laying have also inhibited captive programs. Additionally, migration routes need to be taught to the captive-bred whooping cranes. Chassahowitzka National Wildlife Refuge in Florida and Necedah National Wildlife Refuge in Wisconsin host a non-natural migratory population that was trained to fly south for the winter for their very first migration by a human-piloted ultralight aircraft. Once birds have been trained, they are able to successfully complete future migrations and reduce deviation from their path more and more effectively as they gain years of experience [7, 8].

Captive-born cranes must be taught the migratory routes via lightweight airplane. [Source: USFWS]

To add to all of the issues experienced by both in situ and ex situ approaches, all populations risk negative effects from inbreeding (also known as inbreeding depression). All currently living whooping cranes come from only 16 whooping cranes that were alive in the early 1940s [9], and the loss of genetic variation can have negative consequences for the animals’ ability to breed and survive. While these breeding efforts have increased population numbers, more support is needed for whooping crane conservation programs working to save this endangered species.

When in human care, juvenile whooping cranes must be fed from a person wearing an adult whooping crane costume (Note the adult whooping crane puppet!). Using a costume prevents the young from imprinting on humans. Imprinting is when a young animal forms a strong bond with a parent, which can affect its ability to form relationships with other animals once reintroduced into the wild. [Source: Steve Hillebrand/USFWS]

In the United States, conservation programs and legislature including the Endangered Species Act of 1973 have sustained whooping crane populations. Even before the Endangered Species Act was enacted, a federal law known as the Migratory Bird Treaty Act (MBTA) of 1918 safeguarded the species for many years. Under the MBTA, whooping cranes, along with many other migratory bird species, are protected from threats imposed by people. Still, human activity continues to pose a threat to many of these important species. You can protect migratory birds in a variety of ways! These ways include, but are not limited to:

  • Keeping cats indoors to prevent millions of birds from being killed annually.
  • Using special window treatments to prevent birds from colliding with glass.
  • Creating a natural habitat in your yard using native plant life and eliminating pesticide use.
  • Supporting bird friendly legislature [10].

Can you think of any ways to support these bird populations? Whooping crane populations were devastated almost to the point of extinction by humans – it’s now our responsibility to ensure that they, along with other species like them, remain well-protected moving forward.

A Louisiana Department of Wildlife and Fisheries employee in a whooping crane costume opens fencing from a top-netted pen to let birds into an open pen. [Source: Gabe Giffen/LDWF]

Lindsey Broadus is a PhD candidate in the Animal Behavior Graduate Group. She is interested in the long term effects of early experiences on adult behavior and physiology (and currently studies ducks in captivity).


References:

  1. “Quivara National Wildlife Refuge: Whooping Crane, Grus americana“. U.S. Fish & Wildlife Service. Retrieved 05 May 2020.
  2. Urbanek, R. P. & Lewis, J. C. (2020). Whooping Crane (Grus americana), version 1.0. In Birds of the World (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.whocra.01
  3. BirdLife International. (2019). Grus americana (amended version of 2017 assessment). The IUCN Red List of Threatened Species 2019: e.T22692156A155547970. https://dx.doi.org/10.2305/IUCN.UK.2017-1.RLTS.T22692156A155547970.en. Retrieved on 05 May 2020.
  4. Kuyt, E. (1996). Reproductive manipulation in the Whooping Crane Grus americana. Bird Conservation International, 6(1), 3-10. doi:10.1017/S095927090000126X
  5. Boyce, M. S., Lele, S. R., & Johns, B. W. (2005). Whooping crane recruitment enhanced by egg removal. Biological Conservation, 126(3), 395–401. https://doi.org/10.1016/j.biocon.2005.06.011
  6. U.S. Fish and Wildlife Service. (1994). Whooping Crane recovery plan. U.S. Fish and Wildlife Service Albuquerque, NM.
  7. Urbanek, R., Fondow, L., Zimorski, S., Wellington, M., & Nipper, M. (2010). Winter release and management of reintroduced migratory Whooping Cranes Grus AmericanaBird Conservation International, 20(1), 43-54. doi:10.1017/S0959270909990153
  8. Mueller, T., O’Hara, R. B., Converse, S. J., Urbanek, R. P., & Fagan, W. F. (2013). Social Learning of Migratory Performance. Science, 341(6149), 999-1002.
  9. Brown, M. E., Converse, S. J., Chandler, J. N., Crosier, A. L., Lynch, W., Wildt, D. E., Keefer, C. L., & Songsasen, N. (2017). Time within reproductive season, but not age or inbreeding coefficient, influences seminal and sperm quality in the whooping crane (Grus americana). Reproduction, Fertility and Development, 29(2), 294-306.
  10. American Bird Conservancy. (2010). From the American Bird Conservancy: top 10 things you can do in your home or yard to help declining migratory birds. American Bird Conservancy. https://abcbirds.org/article/migrating-birds-could-use-a-helping-hand-ten-ways-people-can-protect-birds-this-spring/. Retrieved on 05 May 2020.

Main image by Graham Veal [Source].


Edited by Meredith Lutz.

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