December 29, 2020

Fertility and welfare

The number of offspring wild animals produce is determined by the strategy that maximizes the spread of their genes, not the welfare of their offspring. This means that if there is ever a time of plenty, higher fertility rates (e.g., Ruffino et al. 2014) will cause the population to grow until fertility rates equal mortality rates again (Hixon 2008).

This used to be the case in human societies (Roser 2013), but contraceptives and changing social norms have allowed humans to take some control of how many offspring we have, contributing to longer life expectancies and higher average quality of life in many parts of the world (Clark 2008, Roser 2017). In this blog post, I will discuss how we could extend similar privileges to other animals.

Why contraception?

Contraception for wild animals seems like a very promising place to start. (See Brennan 2018 for a summary of wildlife contraception methods). If there is a fixed amount of available resources, contraception will increase the amount of resources available to each individual, giving them better odds of having high welfare. If properly administered, contraception programs might allow all individuals in a population to meet their needs for food and shelter.

Contraception for wild animals is already being studied and used in a number of species, including wild horses, prairie dogs, rats, deer, coyotes, rabbits, geese, pigeons (see here for some examples), and even ants (Tay & Lee 2014). However, these wildlife contraceptive programs are primarily intended to benefit humans by reducing the populations of animals we deem to be pests. In order to design ecologically sound fertility interventions with the goal of improving wild animals’ lives, we must measure contraception’s impact on the average welfare of the target species and at least preliminarily assess the indirect effects on non-target species.

Our project

Some research has been conducted on the effects of contraception on physiological indicators of stress (Gray 2010), although rarely with an explicit focus on welfare. In order to fill this knowledge gap, Wild Animal Initiative researchers worked with stress physiology expert Ignacio Moore (a member of our board) to develop a project studying pigeon welfare in populations treated with contraceptives. We are currently seeking funding to begin this project.

The reproductive inhibitor OvoControl-P, consisting of bait containing 5000 ppm of the active ingredient nicarbazin, has been used since 2007 as a non-lethal method to shrink rock pigeon (Columba livia) populations in the US (Fagerstone et al. 2008). We predict that treating wild flocks of pigeons with OvoControl over the course of several years will reduce the fertility rate of the treated female pigeons (Avery et al. 2008), although we don't know by how much (Senar et al. 2020).

Living in a population that is further from the carrying capacity of the local environment is probably good for the average welfare of pigeons of all ages. We think this welfare benefit will partly come from an increase in life expectancy, because reduced competition for food after a population decline should decrease starvation and improve survival.

The study will be conducted in the northeastern United States, where multiple flocks of pigeons will be treated with OvoControl or a placebo bait. Because it is impossible to measure the subjective experience of welfare directly, we will estimate the effects using a combination of proxies such as stress hormone levels, telomere attrition, body condition, and disease prevalence. We’ll collect this data over two years.

Unfortunately, we don't know whether we will be able to detect population-level welfare effects within the study period. Thankfully, we expect to observe some of the effects immediately if they occur at all. For example, female pigeons usually lay two eggs at a time, but OvoControl decreases the likelihood that both eggs are fertilized (Avery et al. 2008). This means that a larger fraction of the nestlings will grow up without sibling competition, which will allow them to obtain more food and care from their parents (Hetmański & Barkowska 2008, Stock & Haag-Wackernagel 2016). It then seems reasonable to expect that the average effect of OvoControl on nestling welfare will be positive.

When it comes to adult welfare, the picture is less clear. If parents only have to raise one offspring at a time instead of two, they might benefit from the contraception. But if neither of the eggs hatch, they will likely abandon the infertile eggs and attempt to breed again (Jacquin et al. 2010). Laying a second set of eggs unusually soon after the first might have a negative effect on the mother’s welfare, and the net effect of these physiological changes for females is unclear.

Ultimately, we want to develop a complete understanding of the welfare consequences of pigeon contraceptive administration not just on pigeons, but on all affected animals. Administering pigeon fertility control may change the overall size of the target pigeon population, and will certainly affect the age structure. These effects may have welfare-relevant impacts on animals who interact with the pigeons. To know whether, on net, administering contraceptives are good for all animals affected requires building up our knowledge of the relevant communities and system-level effects.

Small-scale projects like the one we are proposing are important for testing our predictions about the welfare effects of interventions. Over time, we hope to conduct or support multiple projects concerning different aspects of the pigeon community, chipping away at our unknowns to understand the system as a whole. And if contraception turns out to improve pigeon or broader community welfare, this project could lead to large-scale pigeon welfare programs, inspire the development of contraception programs for other species, or simply demonstrate the tractability of responsibly improving wild animal welfare.

Securing funding

Wild Animal Initiative typically supports field research by helping academic labs secure funding through our Grant Assistance Program. But because we already have the necessary expertise on our team, in this case we think it would be more effective to conduct the work ourselves. Seeking funding for the project ourselves also gives us the chance to explore the proposal systems of a wide range of funders, potentially identifying more groups that could support work on wild animal welfare. There are many considerations affecting the effort we put into securing funding for this project ourselves, but one of the main considerations is the opportunity cost. We are careful about which grant opportunities we pursue in order to avoid spending our limited time and energy on projects that don’t optimally advance our mission, and to avoid diverting funding from other highly effective projects.

Our study proposal constitutes the start of a longer term project. We would love to hear from other researchers who would like to contribute to a complete picture of the consequences of contraceptive administration for pigeons or other animals.

References

1. Avery, M. L., Keacher, K. L., & Tillman, E. A. (2008). Nicarbazin bait reduces reproduction by pigeons (Columba livia). Wildlife research, 35(1), 80-85. https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1989&context=icwdm_usdanwrc.

2. Brennan, O. (2018). Wildlife contraception. Retrieved December 28, 2020 from http://web.archive.org/web/20210729112612/https://was-research.org/paper/wildlife-contraception/.

3. Clark, G. (2008). A farewell to alms: a brief economic history of the world (Vol. 25). Princeton University Press.

4. Fagerstone, K. A., Miller, L. A., Eisemann, J. D., O’Hare, J. R., & Gionfriddo, J. P. (2008). Registration of wildlife contraceptives in the United States of America, with OvoControl and GonaCon immunocontraceptive vaccines as examples. Wildlife Research, 35(6), 586-592. https://pubag.nal.usda.gov/download/21393/PDF.

5. Gray, M. E., & Cameron, E. Z. (2010). Does contraceptive treatment in wildlife result in side effects? A review of quantitative and anecdotal evidence. Reproduction, 139(1), 45–55. https://repository.up.ac.za/bitstream/handle/2263/16950/Gray_Does%282010%29.PDF?sequence=1.

6. Hetmański, T., Barkowska, M. (2008). Breeding parameters and recruitment in feral pigeons Columba livia f. domestica. Acta Ornithologica 43:159-166. https://www.researchgate.net/profile/Tomasz_Hetmanski/publication/233579208_Breeding_Parameters_and_Recruitment_in_Feral_Pigeons_Columba_livia_f_Domestica/links/59dbb5b8aca2728e20182ca8/Breeding-Parameters-and-Recruitment-in-Feral-Pigeons-Columba-livia-f-Domestica.pdf.

7. Hixon, M. A. (2008) Carrying capacity. In: Jorgensen, S.E., Fath, Brian. Encyclopedia of Ecology. London: Elsevier Science. p. 258-260.

8. Jacquin, L., Cazelles, B., Prévot-Julliard, A.C., Leboucher, G., & Gasparini, J. (2010). Reproduction management affects breeding ecology and reproduction costs in feral urban pigeons (Columba livia) Canadian Journal of Zoology 88:781-787. https://cdnsciencepub.com/doi/abs/10.1139/Z10-044.

9. Roser, M. (2017). Fertility rate. Retrieved December 28, 2020 from https://ourworldindata.org/fertility-rate.

10. Roser, M. (2013). Economic growth. Retrieved December 28, 2020 from https://ourworldindata.org/economic-growth.

11. Ruffino, L., Salo, P., Koivisto, E., Banks, P. B., & Korpimäki, E. (2014). Reproductive responses of birds to experimental food supplementation: a meta-analysis. Frontiers in zoology, 11(1), 80. https://link.springer.com/article/10.1186/s12983-014-0080-y.

12. Senar, J. C., Navalpotro, H., Pascual, J., & Montalvo, T. (2020). Nicarbazin has no effect on reducing feral pigeon populations in Barcelona. Pest Management Science. https://onlinelibrary.wiley.com/doi/abs/10.1002/ps.6000.

13. Stock, B., & Haag‐Wackernagel, D. (2016). Food shortage affects reproduction of feral pigeons (Columba livia) at rearing of nestlings. Ibis, 158(4), 776-783. https://onlinelibrary.wiley.com/doi/pdf/10.1111/ibi.12385.

14. Tay, J. W., & Lee, C. Y. (2014). Influences of pyriproxyfen on fecundity and reproduction of the Pharaoh ant (Hymenoptera: Formicidae). Journal of economic entomology, 107(3), 1216-1223. https://academic.oup.com/jee/article/107/3/1216/826561.