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Chirping
I wanted to create a master thread for listing foods that may not be safe for geese (as the previous thread is a decade old and is mostly about dogs eating chocolate and not geese). Please add any anecdotal experience or research you have done!
Avocado leaves/skins
Avocado, especially the leaves/skins, contains a toxin called persin which is largely harmless to humans but can be fatal to birds, including ducks and geese. The flesh of the avocado contains a relatively low concentration compared to the leaves, skins, and pit, but personally I would not recommend feeding it to birds out of an abundance of caution.
Caffeine
Anything that contains caffeine, like coffee or tea leaves, should be avoided as it can cause cardiovascular failure in birds.
Cassava
Cassava root, skin, and leaves contains a high concentration of cyanide. This can be made safe to consume for humans by long periods of soaking followed by cooking, but some small levels of cyanide will still remain. Indisputably toxic when raw, would advise caution if cooked.
Chocolate
Theobromine is as toxic to birds as it is to dogs, and processed chocolate is high in sugar and fat.
Citrus
The high acidity in citrus fruit can cause ulcers, and most geese and ducks will not eat it to begin with because of this. There are some indications it can interfere with calcium absorption as well.
Green tomatoes
Underripe tomatoes and leaves also contain solanine, but in smaller quantities than potatoes. Not really recommended, but certainly less of a risk than potatoes. Ripe tomatoes are fine.
Onions
Alliums like onion and garlic contain thiosulfate compounds. These can cause anemia, cardiac and liver dysfunction, and ulcers when fed. Onions contain a large amount of these compounds, so feeding is not recommended, while garlic contains relatively little and is generally considered safe in small quantities.
Potatoes
Potatoes are a member of the nightshade family. Raw potato stems, leaves, and peels contain high concentrations of the nightshade toxin solanine, which birds are especially sensitive to. It is in lower concentration in the flesh of (non-green) potatoes but still present. Solanine acts as a neurotoxin and can cause seizures, paralysis, and death. Cooking reduces but does not eliminate solanine.
Tobacco
Don't let your geese smoke! But seriously, nicotine, found in tobacco leaves, is a stimulant and can cause toxicity, especially neurological disorder, in birds. Note also that tobacco smoke, or any smoke, can cause respiratory issues as well as eye and sinus irritation.
Oxalic Acid
Several plants are toxic to varying levels due to their high oxalic acid content. Oxalic acid reduces calcium absorption, which can be directly harmful, causing muscular issues, but more importantly for geese and ducks, will weaken egg shells, potentially resulting in egg binding or eggs breaking inside the bird.
Note that high oxalic acid plants can also cause irritation and contact dermatitis if you are growing them near your birds.
Some plants that contain oxalic acid:
Amaranths (including quinoa), leaves and stems
Rhubarb
Raw rhubarb, especially the leaves, contains several toxins, including an excess of oxalic acid.
Spinach
I know! Ducks and geese love spinach, and overall, it's fine, but it contains a high level of oxalic acid, so moderation is advised.
All brassicas (spinach, cabbage, broccoli, etc) contain varying levels of oxalic acid, but as a whole they are in low enough concentrations that moderate consumption is acceptable.
Wood-sorrel (Oxalis)
Oxalic acid gets its name from these plants. They are all extremely high in oxalic acid content.
Other potential sources of toxicity:
Algae
High algae concentrations in stagnant or unclean water sources can be toxic, and generally indicates poor water quality.
Mold
Mold and fungi spores can cause respiratory disease in birds, as well as being directly toxic.
Metal
Animals can develop a disease known as hardware poisoning if they accidentally ingest small pieces of metal like screws or bolts. This can be directly fatal if the ingested object is sharp and punctures the digestive tract. Zinc toxicity is also an especial concern in birds, as anything containing zinc, like pennies, galvanized hardware, etc. will be partially digested and absorbed. Zinc is highly toxic to waterfowl and even a single penny can be fatal.
DISCLAIMER: THIS LIST IS NOT COMPLETE. I am certain there are many, many other toxic substances out there I couldn't find any information about, so always use caution when feeding anything new to your birds.
Note that generally speaking, ducks and geese will have the same sensitivities, and what is toxic to one is highly likely to be toxic to the other.
Avocado leaves/skins
Avocado, especially the leaves/skins, contains a toxin called persin which is largely harmless to humans but can be fatal to birds, including ducks and geese. The flesh of the avocado contains a relatively low concentration compared to the leaves, skins, and pit, but personally I would not recommend feeding it to birds out of an abundance of caution.
Caffeine
Anything that contains caffeine, like coffee or tea leaves, should be avoided as it can cause cardiovascular failure in birds.
Cassava
Cassava root, skin, and leaves contains a high concentration of cyanide. This can be made safe to consume for humans by long periods of soaking followed by cooking, but some small levels of cyanide will still remain. Indisputably toxic when raw, would advise caution if cooked.
Chocolate
Theobromine is as toxic to birds as it is to dogs, and processed chocolate is high in sugar and fat.
Citrus
The high acidity in citrus fruit can cause ulcers, and most geese and ducks will not eat it to begin with because of this. There are some indications it can interfere with calcium absorption as well.
Green tomatoes
Underripe tomatoes and leaves also contain solanine, but in smaller quantities than potatoes. Not really recommended, but certainly less of a risk than potatoes. Ripe tomatoes are fine.
Onions
Alliums like onion and garlic contain thiosulfate compounds. These can cause anemia, cardiac and liver dysfunction, and ulcers when fed. Onions contain a large amount of these compounds, so feeding is not recommended, while garlic contains relatively little and is generally considered safe in small quantities.
Potatoes
Potatoes are a member of the nightshade family. Raw potato stems, leaves, and peels contain high concentrations of the nightshade toxin solanine, which birds are especially sensitive to. It is in lower concentration in the flesh of (non-green) potatoes but still present. Solanine acts as a neurotoxin and can cause seizures, paralysis, and death. Cooking reduces but does not eliminate solanine.
Tobacco
Don't let your geese smoke! But seriously, nicotine, found in tobacco leaves, is a stimulant and can cause toxicity, especially neurological disorder, in birds. Note also that tobacco smoke, or any smoke, can cause respiratory issues as well as eye and sinus irritation.
Oxalic Acid
Several plants are toxic to varying levels due to their high oxalic acid content. Oxalic acid reduces calcium absorption, which can be directly harmful, causing muscular issues, but more importantly for geese and ducks, will weaken egg shells, potentially resulting in egg binding or eggs breaking inside the bird.
Note that high oxalic acid plants can also cause irritation and contact dermatitis if you are growing them near your birds.
Some plants that contain oxalic acid:
Amaranths (including quinoa), leaves and stems
Rhubarb
Raw rhubarb, especially the leaves, contains several toxins, including an excess of oxalic acid.
Spinach
I know! Ducks and geese love spinach, and overall, it's fine, but it contains a high level of oxalic acid, so moderation is advised.
All brassicas (spinach, cabbage, broccoli, etc) contain varying levels of oxalic acid, but as a whole they are in low enough concentrations that moderate consumption is acceptable.
Wood-sorrel (Oxalis)
Oxalic acid gets its name from these plants. They are all extremely high in oxalic acid content.
Other potential sources of toxicity:
Algae
High algae concentrations in stagnant or unclean water sources can be toxic, and generally indicates poor water quality.
Mold
Mold and fungi spores can cause respiratory disease in birds, as well as being directly toxic.
Metal
Animals can develop a disease known as hardware poisoning if they accidentally ingest small pieces of metal like screws or bolts. This can be directly fatal if the ingested object is sharp and punctures the digestive tract. Zinc toxicity is also an especial concern in birds, as anything containing zinc, like pennies, galvanized hardware, etc. will be partially digested and absorbed. Zinc is highly toxic to waterfowl and even a single penny can be fatal.
DISCLAIMER: THIS LIST IS NOT COMPLETE. I am certain there are many, many other toxic substances out there I couldn't find any information about, so always use caution when feeding anything new to your birds.
Note that generally speaking, ducks and geese will have the same sensitivities, and what is toxic to one is highly likely to be toxic to the other.
