Diets and feeding methods of captive seabirds in mixed enclosures (Rissa tridactyla, Uria aalge, Fratercula arctica and Somateria mollissima).
Dronten University of Applied Sciences
Supervisors: Dionne Slagter, Harald Schmidt, Assessor: Irma Schouwenaars
Bass Rock is the enclosure of four seabird species in Rotterdam Zoo: Black-legged kittiwakes (Rissa tridactyla), common guillemots (Uria aalge), Atlantic puffins (Fratercula arctica) and common eiders (Somateria mollissima), together with some fish species: sea perches, sea bream and crayfishes. The feed and feeding method is the same for several years, unknown is whether diets and feeding methods are sufficient for these types of birds. This study investigated on which way seabirds, in mixed enclosures, can be provided in nutritional needs in a way that is as close as possible to their natural situation. The main question of research is: “How should the seabirds at Rotterdam Zoo be provided in their nutritional needs in a way that is as close as possible to their natural situation?”
The aim of this study was to investigate the most optimal foraging situation for seabird species which are the same, or similar to, as species present in the Bass Rock enclosure in Rotterdam Zoo. The information of this study can be used as principle research in other zoos and other instances, and will also be shared with the European Organisation for Zoos and Aquaria (EAZA). Expected was that the current diet of birds in Rotterdam Zoo provides the birds in nutritional needs, but that there was a lack of scientific information.
Information was gathered by way of literature study, behavioural study and questionnaires to other zoos. Literature study was done to investigate nutritional needs and foraging behaviour in wild and captivity. Behavioural study was done within four weeks by way of scan-sampling per bird species. The recording rule was instantaneous sampling and questionnaires were answered by 31 zoos to investigate diets and methods in other zoos.
Natural diets and foraging behaviour were not always evidenced by scientific research. Evidenced is that the gastrointestinal tract differs a little bit from non-piscivorous birds: The gizzard is relatively small and less muscled. The salivary glands are less important, because seabirds eat mostly wet food items. Seabirds have also salt glands to filter salts of the body, other birds do not have these glands. Bigger kidneys are needed for filtering salt out of the body. The crop of seabirds has mostly no function, because seabirds have a very elastic oesophagus and stomachs. Fermentation of nutrients is the same as in other, non-piscivorous birds, but the caeca are less important. Seabirds are able to detect preys due to well-developed olfactory and visual senses, and are able to remember conditions and places to successfully catch preys. Skin and feathers are also important factors related to the condition of birds. Feathers showing fault bars can be signs of malnutrition. Malnutrition can also cause other problems with plumage of birds.
Nutrients that are considered as important nutrients for seabirds are: methionine and cysteine, which are limiting amino acids, the fatty acids: linoleic acid and α-linoleic acid, calcium and some vitamins. Vitamin requirements are based on experiences, but not scientific improved. Vitamin A (retinol and carotenoids), B1 and E are considered as important vitamins, because these vitamins are broken down during freezing- and storage processes. Frozen fish lack a sufficient amount of these vitamins. These vitamins, and also carotene, vitamin D, vitamin C and folic acid can be influenced by light, heat and/or air or oxygen.
Literature study in diets and behaviour of individual bird species has shown that all four types of birds show different types of behaviour to catch preys. The Atlantic puffin is considered as most social bird, followed by common eiders. Alcidae and gulls can show aggressive behaviour and gulls can even kill other seabirds. The variety of food items and prey types also vary among the bird species.
Diets of captive seabirds also differs a lot. Common eiders are primarily fed on commercial diets and other birds on fish, including some additives. Additives are mainly multivitamins, including vitamin B1, E and mostly also vitamin A. Calcium is already present in sufficient amounts in the viscera of fish. Chosen fish species are mainly capelin, lake smelt, krill and herring for Atlantic puffins, black-legged kittiwakes and common guillemots and smelt for common eiders besides commercial feed. Most zoos feed their animals twice or thrice a day. Preferences for Atlantic puffins, black-legged kittiwakes and common guillemots are mainly preferences for some fish species (capelin, herring, silversides and krill), but common eiders do not seem to have any preferences.
A behavioural study in Rotterdam zoo shows a significant preference for feeding bowl for the Atlantic puffin and kittiwakes. The left bowl was more attractive than the right one. There was no significant evidence for the preference of feeding time. The time spent on foraging compared to other behaviour seem also be way less than foraging behaviour in wild. Common eiders did not show even foraging behaviour, besides only eating from the feeding bowl and have showed some stereotype behaviour. The current diet of Atlantic puffins, black-legged kittiwakes and common guillemots in Rotterdam Zoo consists mostly of one type of feed per day, while other zoos feed different types of fish per day.
A wide variety of feeding methods are used in other zoos. Atlantic puffins, black-legged kittiwakes and common guillemots are mainly fed by using bowls in combination with food scattered in the water, some zoos feed their birds by hand. Only three zoos use only bowls as feeding method. Hand feeding is the most time-consuming method, but ensures the individual food intake. Bowls are less time consuming and makes food available during the whole day, but there is no individual control and other wild birds can steal food. Scattering in the water stimulates diving and hunting behaviour and the individual intake of birds can be controlled more easily, compared to feeding in bowls. A disadvantage is that food scattered in the water can influence the water quality negatively, which can influence the plumage of birds. Common eiders are mainly fed with feed scattered in the water or a combination of bowls and scatter feed in the water. One zoo uses a cage over the water to prevent wild birds eating from the pellets.
Recommended is to vary given fish species per day and add some carotenoids in the diet of Atlantic puffins, black-legged kittiwakes and common guillemots to fill up the shortage of vitamin A. The bowls should be placed on more different places in the enclosure. This method of feeding can be varied by giving some low-fat fish in water as enrichment, but there must be ensured that fish species in the enclosure do not eat too much of this fish. Common eiders should be given more enrichment to reduce stereotype behaviour by giving bowls of grain in different places in the water and giving some blue mussels as enrichment. The current diet can be used, but scatter this food in the water can improve the foraging behaviour. Unknown is whether other birds and fish eat from the pellets.
Recommended for further research is to investigate requirements of different species, or at least for seabirds and sea ducks in general. Behavioural research in Rotterdam zoo can be extended and compared to behavioural studies in other zoos. Behaviour of common eiders should also be investigated to improve health and welfare of the birds. Rotterdam Zoo should consider whether the composition of the birds in Bass Rock should be changed. The last recommendation is to investigate the effects of fish fed in the water to the water quality and bird's plumage.