What’s on the Line? Powerline Collisions in Reintroduced Whooping Crane Populations

Transmission powerlines (left) compared to distribution powerlines (right) in the United States. Photos from Sarah Westin, M.A., and Robert Zullo, States Newsroom

As urban areas expand, so does the need for infrastructure, and it is expected that the global electric grid will continue to expand by 5% every year. However, the expansion of human development and energy infrastructure into vital habitat for both migratory and nonmigratory bird species has led to a large increase in fatal collisions with powerlines. In the United States alone, approximately 12.6-64 million birds are killed from powerline collisions and electrocutions annually. Some tools, such as flight diverters, exist to alleviate these causes of mortality, but while powerline markers and flight diverters can be beneficial in preventing collisions, the cost of implementing these measures into all areas that pose a risk to birds in flight is far too large to make it an effective and realistic solution. To be most effective, our team investigated a crane’s biological risk for collision and identified areas of high collision risk to prioritize where and when flight diverters should be employed.

Whooping Cranes are one of the rarest birds in the world, with only ~690 birds surviving in the wild today. They are particularly susceptible to collisions with powerlines, many of which are fatal, and this impedes the recovery of the species. Powerline collisions account for a significant proportion of mortality events for Whooping Cranes, including up to 39% in some reintroduced populations. This is concerning as the goal of the reintroductions is to become self-sustaining, and to do that we need to gain a clearer understanding of the threats inhibiting this goal, including when that threat is greatest, and identify opportunities to reduce mortalities to ensure the success of the species.

To understand why powerlines pose such a large threat for Whooping Cranes, it is important to recognize the biological and environmental factors that contribute to their risk. Biologically, the sheer size of Whooping Cranes – standing five feet tall with a wingspan of eight feet on average – makes it difficult for them to easily and quickly maneuver when encountering a threat or obstacle and puts them more at risk for a fatal powerline collision compared to many other avian species. Additionally, two of the four Whooping Crane Populations in the US are migratory, and unfamiliarity with areas they fly over during migration can also make them more likely to encounter new or existing powerlines. A study by the International Crane Foundation aimed to identify the factors that contribute to high mortality rates from powerline collisions in order to anticipate higher-risk areas for Whooping Cranes. Subsequently, managers can prioritize key areas to mark and may be able to adjust release areas accordingly.

The International Crane Foundation and crane conservation partners examined mortalities from four reintroduced Whooping Crane populations in the United States, all of which are located within the species’ historic range. To identify Whooping Cranes that suffered fatal collisions with powerlines, all individuals were banded with a USGS numbered band, unique color bands, and a few individuals received transmitters to track their movements. This allowed the team to keep track of individual birds’ whereabouts and survival status. When a mortality was reported and a carcass was recovered, data such as the distance to the nearest powerline and human development were taken, and when possible, necropsies were performed to determine the cause of death. Mortality from a powerline could also be confirmed if a Whooping Crane was located directly beneath a powerline, had broken bones from impact with the line, or showed evidence of electrocution.

In total, 65 fatal powerline collisions were recorded within reintroduced Whooping Crane populations from 1977-2023. Across all populations, there was no significant difference between the number of males and females that struck powerlines, but within the two nonmigratory populations, males did account for significantly more collisions than females. Some theories suggest that males were more likely to lead flocks in flight, which could explain the higher number of collisions for them compared to females. Age was also a contributing factor, and across all populations 73.8% of individuals killed by powerline collisions were under three years of age, therefore considered juveniles or subadults. This could be a result of inexperience migrating, an unfamiliarity with the flight paths they are taking, and fewer skills maneuvering collision risks. Additionally, collisions occurred more frequently when cranes were flying in a group rather than alone. Past studies have found that larger flocks may result in trailing birds having an obscured view and not being able to react as quickly when encountering a powerline. We did not have the ability to document the location of the bird in a flock and can’t say if this is true, but it may explain the frequency of collisions within flocks rather than individuals.

The months in which collisions were most common were in the spring, specifically March and April, and greatest during migration for the two migratory populations. During migration, birds are more likely to fly long distances, through unfamiliar areas, in flocks, and at lower altitudes near stopover sites, all of which could be factors putting them more at risk for powerline collisions. Additionally, of the cases in which time of death was known, powerline collisions were occurring more frequently in low-light conditions around dusk or dawn, although the sample size was small for evaluating this factor. We observed an equal risk of colliding with transmission and distribution lines. Transmission lines are 18.3-50m tall and carry high voltage electricity whereas distribution lines are only 6.4-14.6m tall and carry electricity from substations to homes or businesses. Distribution lines are five to six more times more common than transmission lines in the US, but previous studies of Sandhill Cranes on migration found a four times greater risk of colliding with transmission lines. In our study we also saw an increase in collisions with transmission lines on migration, but an equal risk of collision on summering and wintering grounds. We also observed that most collisions were with lines running N-S and E-W, and collisions on migration were most frequent with E-W lines perpendicular to their direction of travel.

This research provides important insight into biological, environmental, and structural factors that can be taken into consideration when implementing management plans to reduce a Whooping Crane’s risk of fatal collision with a powerline. With collisions occurring more frequently in migratory populations during migration and under low-light conditions, focusing efforts on adding markers to powerlines along stopover sites throughout their flyway as well as including glow-in-the-dark markers, markers that use UV-A light, or acoustic signals could help mitigate these collisions. More data is needed to further evaluate the effectiveness of these markers for Whooping Cranes, but this research furthered our understanding of risks contributing to powerline mortalities, allowing managers to make more informed decisions to place flight diverters strategically throughout the range of Whooping Cranes.

We thank Madelyn Sime, Hillary Thompson, Eva Szyszkoski, Sara Zimorski, Timothy Dellinger, and Stephanie Schmidt, the authors of the paper “Powerline Collisions in Reintroduced Whooping Cranes (Grus americana),” for permitting us to share their work.

Story submitted by Eleanor Laack, Crane Conservation Fellow, and Stephanie M. Schmidt, Lead Outreach Biologist, International Crane Foundation.

Reference: Sime, M.J., Thompson, H.L., Szyszkoski, E.K., Zimorski, S.E., Dellinger, T.A., Schmidt, S.M., 2024. Power-Line Collisions in Reintroduced Whooping Cranes (Grus americana). Southeastern Naturalist 23, 194–211.