Diet and finch health, reproduction and survival.
Dr Sarah Pryke
Aim:This extensive work was done to determine whether the supplements and diets we were feeding at Save The Gouldian Finch research facility improved finch health, reproduction and survival – and if so, how and by what magnitude? This work was required to ensure the diets we were using matched, as near as possible natural diets, with a view to eliminating the possibility of negatively affecting or altering the results of other key research work.
Gouldian finches were the main focus, although we also did some similar diet experiments with the closely related parrot finches – both of these finches are granivorous, have relatively restricted diet in the wild and don’t (or rarely) supplement themselves or offspring with insects. But these supplements have been and continue to be provided to a range of unrelated finches and birds, including long-tail finches, crimson finches, weavers and chats.
Experiments used Gouldian finches of the two main wild head-colour morphs (red and black). Birds were always paired to partners of the same head colour (to remove any maternal effects, e.g. egg sizes, sex ratios, etc. from females paired to males that they consider inferior). We used a total of 60 pairs of Gouldians for this work. Birds were divided into two groups – supplemented (S) and non-supplemented (NS). Both groups were feed unlimited dry seed. This was a custom mix, containing a range of seeds, as shown below in Table 1.
Table 1. The STGF custom seed formula
% of mix
The S group received ¼ teaspoon per bird of freshly sprouted or green seed and supplement daily, and this was increased to 2 tablespoons per cage (parents and offspring) when they had young. The supplement was PRIMA (now sold by Naturally for Birds). PRIMA is a complete and balanced softfood providing a full compliment of nutrients. The nutritional content is shown in Table 2. The NS group did not receive any supplement or sprouted or green seed.
Table 2. Nutritional details for the Naturally for Birds supplement PRIMA
Energy and Carbohydrates
|Dry Matter Digestibility
|Digestible Organic Matter
For the breeding experiments, a male and female were paired together and placed in a cage with no other birds. To fully understand the effect of the diets, and to isolate any potential genetic and environmental effects, we used a very conservative but very powerful experimental design whereby every pair bred twice, once on the S diet and once on the NS diet (with diet order randomised). In other words, half the pairs were given the S diet first (and the other half the NS diet) and they were all allowed to breed. Then once the offspring were weaned at 60 days of age, the nest box was removed from the cage and the adults were put on the alternative diet for 4 weeks (this was to eliminate the effects of the diet before breeding). After 4 weeks, a nest box was returned and they were allowed to breed again. This means that all results are within-individual effects (i.e. the same female raised X offspring on one diet, and Y offspring on other diet – and therefore very conservative, robust and convincing!!).
It is important to note that these experiments were not designed to test the effect of just the PRIMA supplement or just the green/sprouted seed. We had already designed the formulation of PRIMA (containing 23 different components) to provide a balanced compliment of nutrients when fed in combination with sprouted seed. The energy value, digestibility and appropriate level of protein were specifically designed.
Females on the S diet laid slightly bigger clutches of eggs than when they were on the NS diet. Females on S diet laid an average of 6 eggs but when on the NS diet they laid 5 or fewer eggs.
Females on S diets also laid significantly larger eggs than when they were on the NS diets. Egg size is a very important predictor of future fitness – individuals from bigger eggs in a range of bird species have consistently been found to be larger at birth, growth faster and be more likely to survive. Indeed, egg size is often considered a key measure for predicting the future health and survival probability of birds. Chick growth rates, from hatching to fledging (leaving the nest)) also differed substantially between the two diets with chicks reared on the S diet growing 40% faster than chicks reared on the NS diet.
It is important to note that chicks were cross-fostered between nests (i.e. swapped) so parents are not rearing their own genetic chicks and instead have foster/adopted kids in the nest. This is done to remove the previous reported effects of diet on egg number and egg size (i.e. the effect of diet reported/shown here on growth rates is not because of larger eggs laid by females on the S diet; instead it is related solely to the diet fed to the chicks). This adoption technique is a powerful way of allowing us to identify how diet affects each measured stage, independently of genetics and the early development environment (i.e. clutch size, egg size, female hormones, female condition, etc.).
There are also diet-related sex differences between growth rates. Offspring of both sexes grew equallyfast on the S diet, but on the NS diet, males grew faster than females. Therefore daughters do worse on lower-quality diets. This suggests yet another factor which can distort sex ratios in finches.
Chicks from hatching to fledging (leaving the nest) were also found to be much healthier (>40%) when reared on the S diet compared to those reared on the NS diet. We use a number of indices to measure health, but one of the most useful and powerful physiological measure is haemoglobin concentration (measured from a drop of blood) as this response is strongly related to nutrition, immune function and general health in birds.
Proportionallymore birds reared on the S diet also survived to sexual maturity than those reared on the NS diet. Sexual maturity here is measured at 1 year of age (since hatching). And this effect was independent of post-parental care as after birds were weaned from their parents (day 60) they were all placed on the same S diet. This means that dietary effects early in life have long term consequences on survival and health. Amongst groups of adults fed the two diets for6 months, we also found that survival rates were substantially higher (>30%) among birds on the S diet compared to the NS.
Similar experiments were also carried out with blue-faced parrot finches. Parrot finches showed similar effects with females laying larger clutches and eggs on the S diet and also rearing larger, healthier and faster growing offspring.
Previously published results on Gouldian finches show that females on lower quality diets altered the sex of their offspring to produce more sons than daughters (because daughters do worse on low quality diets than sons). Similar to this, parrot finches show the same effects – females fed the NS diet produce more sons compared to females fed the S diet which produce an equal sex ratio. This seems adaptive for the finches because daughters are particularly susceptible to diet and require a higher quality (and higher protein diet) to successfully survive to adulthood.
Not surprisingly, diet is key to the health and survival of birds! But what is surprising is the magnitude of the effect. This is especially so since most of the reproductive measures we have made are within-females, such that the same female is substantially altering the number and size of her eggs (and sex of her offspring) in response to diet changes.Overall, the PRIMA supplement and green or sprouted seed produced far healthier, larger and older individuals than using dry seed alone. We know that the green or sprouted seed would have generated some of this effect, but PRIMA provides a much broader range of nutrients that the green or sprouted seed and excellent levels of easily assimilated protein.
Importantly, diet quality is fundamental early in life and has long-term effects – what mothers are fed can actually affect the size, lifespan and health of a chick, and what chicks are fed in the nest affects their survival to adulthood, and this is irrespective of the diet they get for the 9 months after leaving the nest and before reaching sexual maturity. The PRIMA supplement used in these experiments is available through NATURALLY FOR BIRDS Pty Ltd at www.naturallyforbirds.com.au . Naturally For Birds was formed to make available to general aviculture the scientifically proven diet supplements we developed during the research at Save the Gouldian Fund facilities. Naturally for Birds directs all profits to Save The Gouldian Fund to fund further work on finch health and nutrition.