Lack of observed movement response to lead exposure of California condors

Abstract

Lead poisoning is an important conservation concern for wildlife, and scavenging birds are especially at risk from consumption of carcasses of animals killed with lead ammunition. Because current methods to identify lead exposure require animal capture and blood collection, management would benefit from the development of a less costly and noninvasive behavioral test for illness in wild animals. We attempted to design such a test to identify lead exposure in California condors (Gymnogyps californianus) that we tracked with global positioning system (GPS) telemetry in southern California, USA, 2013-2016. We measured blood-lead concentrations in tracked birds and expected that flight behavior would be influenced by lead exposure; thus, we measured the effect of blood-lead concentrations on 2 different types of movement rates and on the proportion of time condors spent in flight. We found no effect of lead exposure on any of these 3 behavioral metrics. Our work suggests that the measurements we took of flight behaviors were not a useful tool in predicting lead exposure in the mildly to moderately exposed birds we studied. Wild birds are effective at hiding illness, especially condors who have a strong social hierarchy in which showing weakness is a disadvantage. However, focusing on behaviors other than flight, expanding the sample studied to include birds with a wider range of lead concentration values, or analyzing tissues such as feathers (rather than, or in addition to, blood) may be more useful for identification of lead exposure and other diseases that may limit wildlife populations. Ó 2017 This article is a U.S. Government work and is in the public domain in the USA.

Ground Ingredients: Analysis of Lead Exposure in the California Condor’s (Gymnogyps Californianus) Ground Foraging Habitat

“…Once captured, biologists from the United States Fish and Wildlife Service (USFWS) restrained the birds to draw blood from the medial metatarsal vein and place the blood samples in tubes with a dipotassium ethylenediaminetetraacetic acid (K2-EDTA) additive (Poessel et al, 2017).…”

“…These samples were analyzed to obtain the lead concentration in the certified commercial laboratory at the California Animal Health and Food Safety Laboratory, University of California, Davis using graphite furnace atomic absorption spectrometry on a PinAAcle 900z (PerkinElmer, Waltham, MA, USA). The certified commercial laboratory's method allows for a detection limit of approximately 5 µg/dL, therefore, any level below this detection limit is considered as a value of 0 (Poessel et al, 2017). The threshold at which a condor begins to show physiological symptoms of lead poisoning was determined to be 20 µg/dL in a study by Finkelstien et al in 2012, however, the actual level at which a condor begins to suffer from these symptoms is not well understood.…”

“…While these advances have allowed for more advanced exploration of the condors' exposure to many risks, analyses still primarily focus on exposure to risks during flight rather than while on the ground (Meretsky and Snyder, 1992;Hunt et al, 2008;Kelly et al, 2014, Poessel et al, 2018. Previous researchers have discussed the landscape characteristics that could potentially contribute to lead exposure such as land use, land ownership, and land management (Kelly et al, 2014;Poessel et al, 2017). Until recently, most spatial studies did not explore the risks that condors encounter on the ground while feeding or resting, but with the advancement of tracking devices such as the CTT-1070 GPS units, researchers now have the ability to differentiate ground foraging points (Hall et al, forthcoming 2019) from other telemetry point data.…”

“…Since condors were first equipped with patagial tracking devices in the early 2000s, few studies have analyzed the specific spatial components of lead exposure (Hunt et al 2006, Finkelstein et al, 2010Kelly et al, 2014;Poessel, 2017). isotopic feather sequential analytics to identify a highly precise and accurate measure of the condors' day-to-day lead exposure for up to a 4-month span (2010).…”

“…Research also tells us that understanding condor response to lead poisoning at specific measurements (ie. µg/dL) is difficult due to the strong social hierarchy present amongst condors that drives them to likely hide a potential illness rather than reveal weakness (Poessel et al, 2017).…”