actions should be directed to improve it. However, in the short term, SFS can
maintain a large floater surplus that may delay population decline. It is understood
that the eradication of the illegal use of poison is neither easy nor time efficient, and
hence measures taken to allow more time for the application of proper and more
effective management actions can be a useful instrument for conservation. Thus,
efforts to determine adequate tools to reduce poisoning risk among adults are
important as well. In this sense, experimental work is needed to test the effectiveness of smaller, less predictable SFS located near breeding territories to enhance
adult survival while avoiding large aggregations of non-adult birds in their
surroundings.
It is worth noting that the reliability of predictive models depends on the
robustness of demographic rates and the number of known parameters for each age
class. In our case, survival estimates by age classes and fecundity were available
and reliable. Nevertheless, some parameters were unknown, mainly the recruitment
curve and how it changed with variations in density (Tavecchia et al. 2007). Thus,
the structure of the model was a compromise between complexity (due to known
demographic patterns such as age-dependent survival or density-dependent fecundity) and simplicity (due to the unknown parameters such as the percentage of
breeders at each age class). However, several goals to ensure the maximum reliability at the predictive power of extinction risk were achieved in our modelling by
incorporating uncertainty in parameter estimates and stochasticity in population
dynamics (Lande et al. 2003). Finally, it is important to note that demographic
consequences of artificial increments in survival are limited to those included in our
hypothetical scenarios. Complex aspects linked to alterations in natural selection
pressures should also be taken into account since a large proportion of young, that
in more “natural” situations would have died (low-quality individuals; Tavecchia
et al. 2001; Sanz et al. 2008), are now potentially recruited into the breeding
population. Moreover, if only SFS-maintained birds are progressively selected, the
population can become more dependent on human-supplied food than previously
thought.
15.6.5 Usefulness of Supplementary Feeding Sites
for the Conservation of Endangered Populations
Supplementary feeding of wild birds is a widespread practice that may alter the
natural dynamics of food supply, representing a major intervention in avian ecology. Indeed, supplementary feeding has the potential to change long-term population dynamics and distribution ranges of many species (for a revision see Robb
et al. 2008). Therefore, policy-makers and managers have found in supplementary
feeding actions a common, straightforward solution to many different conservation
challenges of endangered populations, including increasing breeding success (e.g.
González et al. 2006; Margalida 2010b; Margalida et al. 2017), providing safe
15 Importance of Long-Term Studies to Conservation …
365
maintain a large floater surplus that may delay population decline. It is understood
that the eradication of the illegal use of poison is neither easy nor time efficient, and
hence measures taken to allow more time for the application of proper and more
effective management actions can be a useful instrument for conservation. Thus,
efforts to determine adequate tools to reduce poisoning risk among adults are
important as well. In this sense, experimental work is needed to test the effectiveness of smaller, less predictable SFS located near breeding territories to enhance
adult survival while avoiding large aggregations of non-adult birds in their
surroundings.
It is worth noting that the reliability of predictive models depends on the
robustness of demographic rates and the number of known parameters for each age
class. In our case, survival estimates by age classes and fecundity were available
and reliable. Nevertheless, some parameters were unknown, mainly the recruitment
curve and how it changed with variations in density (Tavecchia et al. 2007). Thus,
the structure of the model was a compromise between complexity (due to known
demographic patterns such as age-dependent survival or density-dependent fecundity) and simplicity (due to the unknown parameters such as the percentage of
breeders at each age class). However, several goals to ensure the maximum reliability at the predictive power of extinction risk were achieved in our modelling by
incorporating uncertainty in parameter estimates and stochasticity in population
dynamics (Lande et al. 2003). Finally, it is important to note that demographic
consequences of artificial increments in survival are limited to those included in our
hypothetical scenarios. Complex aspects linked to alterations in natural selection
pressures should also be taken into account since a large proportion of young, that
in more “natural” situations would have died (low-quality individuals; Tavecchia
et al. 2001; Sanz et al. 2008), are now potentially recruited into the breeding
population. Moreover, if only SFS-maintained birds are progressively selected, the
population can become more dependent on human-supplied food than previously
thought.
15.6.5 Usefulness of Supplementary Feeding Sites
for the Conservation of Endangered Populations
Supplementary feeding of wild birds is a widespread practice that may alter the
natural dynamics of food supply, representing a major intervention in avian ecology. Indeed, supplementary feeding has the potential to change long-term population dynamics and distribution ranges of many species (for a revision see Robb
et al. 2008). Therefore, policy-makers and managers have found in supplementary
feeding actions a common, straightforward solution to many different conservation
challenges of endangered populations, including increasing breeding success (e.g.
González et al. 2006; Margalida 2010b; Margalida et al. 2017), providing safe
15 Importance of Long-Term Studies to Conservation …
365