How Would An Increase In Nest Sites Affect A Population Of Pigeons?
Supplementary food given to birds can have contemporary effects by reducing the risk of starvation, increasing survival, and altering movements and reproductive performance. There is, however, a widely held perception that birds benefit from extra food over winter, but that it is better that they ‘look after themselves’ during breeding. Here we describe a landscape-scale experiment showing for the first time that the effects of increasing food availability only during the winter can be carried over to the subsequent breeding season. Even though food supplementation stopped six weeks prior to breeding, birds living on sites provisioned over winter had advanced laying dates and increased fledging success compared with birds living on unprovisioned sites. Thus, supplemental feeding of wild birds during winter, in a manner mimicking householders provisioning in gardens and backyards, has the potential to alter bird population dynamics by altering future reproductive performance.
Impact on Breeding Success
The experiment conducted in County Down, Northern Ireland, demonstrated that over winter feeding allows birds to breed earlier, suggesting that food limitation in the months prior to breeding may be a significant factor regulating the initiation of laying. Additionally, supplementary feeding enables birds to enhance their productivity by increasing the number of chicks that fledge successfully. The study focused on blue tits and found that birds at supplemented sites laid an average of 2.5 days earlier than birds at control sites. Controlling for the potential effect of an earlier average laying date, feeding also significantly affected the number of chicks that fledged, with almost one extra chick per nest fledging at supplemented sites compared with controls.
Potential Mechanisms
Although blue tits are income breeders, so that they do not rely heavily on endogenous resources for egg formation, there is likely to be a condition threshold that an individual needs to reach before it can begin breeding. Since feeding stopped over six weeks prior to the first clutch being initiated, the results indicate that supplementation during winter might enable females to enter the breeding season in better body condition, supporting the ‘constraint hypothesis’. Previous studies have found that birds with access to supplementary food have higher levels of plasma protein, an indication of improved body condition, and were able to accumulate endogenous resources. Additionally, the improved breeding success in fed woodlands could also be driven via the provisioning of important micronutrients that can be stored in the liver. In addition to providing carbohydrate, fat, and protein, common feeds such as peanuts and sunflower seeds are excellent sources of other micronutrients (e.g. vitamin E). Birds fed over winter may therefore have benefited from an increased uptake of these specific nutrients and these could be passed on to the chicks via maternal inputs to the eggs.
Ecosystem Implications
Considering the high levels of over-winter provisioning and the marked effects on the populations of birds that commonly use feeders, the impacts on those species that live in close association with human populations may be substantial. In addition, such an extensive over-winter feeding may also influence predictions of the effect of environmental change on the breeding phenology of some species. This may also have wider ecological implications for returning summer migrants that face increased competition from a subsidized resident population of higher population density which is able to breed earlier and produce more offspring.
Conclusion
The study provides valuable insights into the potential long-term effects of increasing food availability for bird populations. It highlights the importance of considering the carry-over effects of winter feeding on subsequent breeding success and population dynamics. The findings suggest that an increase in nest sites, in the form of supplementary feeding during winter, can have a significant impact on the breeding performance of bird populations. This has implications for conservation efforts and urban planning, especially in areas where human-bird interactions are common.
FAQs
1. How does an increase in nest sites affect the breeding success of bird populations?
An increase in nest sites, in the form of supplementary feeding during winter, can lead to birds breeding earlier and increasing the number of chicks that fledge successfully. This can have a significant impact on the population dynamics of bird species.
2. What are the potential mechanisms behind the carry-over effects of winter feeding on breeding success?
Supplementary feeding during winter may enable females to enter the breeding season in better body condition, supporting the ‘constraint hypothesis’. Additionally, the provisioning of important micronutrients that can be stored in the liver may contribute to improved breeding success.
3. What are the wider ecological implications of over-winter feeding on bird populations?
Over-winter feeding may influence predictions of the effect of environmental change on the breeding phenology of some species. It may also have wider ecological implications for returning summer migrants that face increased competition from a subsidized resident population of higher population density.
4. How does over-winter feeding impact the breeding performance of bird populations living in close association with human populations?
The study suggests that over-winter feeding can have substantial impacts on bird species that live in close association with human populations. It can influence breeding phenology and population dynamics, affecting the overall reproductive success of these bird populations.
5. What are the implications of the study for conservation efforts?
The study highlights the importance of considering the carry-over effects of winter feeding on subsequent breeding success and population dynamics. It emphasizes the need to factor in the impacts of supplementary feeding when planning conservation efforts for bird populations.
6. How can the findings of the study inform urban planning in areas with human-bird interactions?
The findings of the study have implications for urban planning, especially in areas where human-bird interactions are common. It underscores the need to consider the long-term effects of increasing food availability for bird populations when designing urban landscapes and green spaces.