Could Egg Removal Lead to Increased Egg Production?

In a 2010 study conducted in Paris, researchers studied feral urban pigeons (Columba livia) to see if egg removal could impact egg-laying cycles. In the study, four pigeon houses with 90 nesting sites were monitored weekly for a 4 year time period. Eggs in the pigeon house were swapped and replaced with fake egg replicas and the nests were monitored, just like Sparrow Swap. One house was used as a control. In this house, eggs were counted weekly but not removed. 

 

In the control house, researchers determined that the pigeons were nesting on an eleven-week cycle. Pigeons perform courtship behaviors and nest build for two weeks, they then incubate eggs for  17-19 days. Chicks are reared in the nest for 6 weeks. After chicks are reared the process then starts over. In the houses where swaps were performed, it was found that pigeons were laying eggs on a four-week cycle. Researchers found that in the houses with swaps, after 18 days of incubation the pigeons would stop incubation, perform courtship behaviors and nest build for two weeks, then lay another clutch.   

With results showing that egg-laying cycles were shortened, researchers then looked to see if the increased egg production was having an adverse effect on female bird health. Swapped eggs were analyzed to determine the proportion of the egg yolk relative to the egg size. An egg with a high proportion of yolk indicates that the condition of the female is good and has laid a high-quality egg. Low yolk proportion can mean the bird is not strong or healthy enough to produce eggs with enough nutrition to support embryonic development.  The researchers found that in houses where swaps had been performed that egg yolk proportion was lower than the yolk proportion in the control house. This means that females who had eggs repeatedly swapped were producing lower quality eggs than those who had not experienced a swap.  

 

What Does This Mean For Sparrow Swap? 

It is possible that the same thing could be happening in nest boxes where repeated swaps are occurring, that is why the follow-up visits to the nestbox are so important. By making follow-up visits and documenting when new eggs are laid in the nest we can see if similar nesting cycles are happening in House Sparrows. Our preliminary results indicate that removing makes House Sparrow renest even faster than in boxes with swaps. This study along with our preliminary results show that management strategies can have unintended consequences. Long term studies are necessary to help get a holistic picture of what happens when management strategies are implemented.  Our Sparrow Swap citizen science partners are crucial to help us understand the long-term effects of House Sparrow management strategies. We depend on the nestbox monitoring data to track trends in House Sparrow reproduction. 

Want to learn more? The full paper for the pigeon study can be found at https://www.nrcresearchpress.com/doi/full/10.1139/Z10-044#.XJkjFShKjIU.

Have questions or comments? Email us at sparrowswap@ncsu.edu 

This post was written by Emily Callicutt. To learn more about Skyler and the rest of the Sparrow Swap Team, check out our Team Page.

References:

Jacquin, L., Cazelles, B., Prévot-Julliard, A., Leboucher, G., & Gasparini, J. (2010). Reproduction management affects breeding ecology and reproduction costs in feral urban Pigeons (Columba livia). Canadian Journal of Zoology, 88(8), 781-787. doi:10.1139/z10-044