A “Meal Deal” for Baby Birds – Is Human Junk Food Contributing to Malnutrition in Corvid Fledglings?

During spring and summer, one can spot magpie or crow fledglings hopping around with their parents in green spaces like parks and backyards or urban areas like sidewalks, parking lots, and around buildings. They are a common feature in most Canadian neighborhoods. Magpies and crows both belong to the family Corvidae, which are known to be intelligent, so it is no surprise that they excel at living in human communities. They thrive in towns and cities despite the many challenges their chosen habitat brings, which is in good part thanks to the easy food availability that humans end up providing to them [1].

However, not every offspring is able to survive – our diagnostic facility in Saskatoon receives many juvenile corvids in spring and summer. There are lots of potential reasons why they did not survive into adulthood, with some being more obvious than others, such as trauma due to vehicle collisions or predation. Occasionally, an interesting observation is made in some of these cases: the fledglings’ limbs, jaws, and beaks are abnormally flexible and rubbery, which is often seen in animals with nutritional deficiencies. We received a fair number of these cases this year, all from within Saskatoon, which got us wondering: could these findings be somehow related to the easily accessible food they find in our waste?

The birds had a similar history of difficulty perching and/or staying on their feet, lethargy, and weakness; sometimes swollen eyes, bent legs, and leg fractures were also noted. On external examination, they presented with abnormally flexible legs and beaks. Upon internal examination, the thyroids and parathyroids (a glandular organ commonly related to metabolic diseases) of some birds also appeared visually enlarged. Interestingly, some of these birds had large fat stores, but juveniles with low body condition were more common.

Our first suspicion was some kind of metabolic disease that led to abnormal levels of calcium, phosphorus, and vitamin D in the body and caused the fledglings’ growing bones to be weak, which can be caused by a poor diet. Signs of metabolic disease have been previously reported in juvenile American Crows: “Diseased birds displayed the presence of either folding fractures or marked valgus (bowing) of one or both tibiotarsi. These birds were paretic and unable to walk or fly […]” [2]. Although considered a possible contributor, the paper did not directly attribute the findings to human food, as the author mentions that crows feed their fledglings with insects. However, a different pattern is noted for magpie species, which have been reported building nests close to trash bins [3] and/or feeding their offspring a diet based around insects, but that also included a notable amount of unnatural food such as meat and wheat products, especially when compared to magpies from rural areas, which eat more insects and less human food [4].

As is often the case, there are more questions than answers. Could this potential metabolic disease be caused by the parents’ preference for tasty junk food or is there a real lack of proper food in cities and the fledglings get whatever is available? Are inexperienced parents more likely to feed less nutritious food to their young, resulting in us examining juveniles that are not representative of the whole population and leading to sampling bias? Does sibling competition lead to weaker juveniles only eating less nutritious food or less food overall, and we are receiving only these weaker birds, also leading to sampling bias? Should we expect fledglings’ bones to have a certain degree of flexibility depending on their age, and if so, how flexible can they be for how long before they become a problem? There are alternative causes of weak bones mentioned in the literature, like ingestion of toxins. These follow-up questions show that, as with anything in science, many variables need to be considered, and further studies would be needed to confirm any suggested cause.

These cases were sent for further histopathological evaluation, where microscopic signs of nutritional deficiencies and other pathological conditions can be assessed. Hopefully, this will shed more light onto the cause of the flexible bones.

If human food is related to this, it would be an ironic fate: The easily accessible human food that helps corvids thrive in urban environments may be hindering their reproductive success. The junk food they seem to love is not enough for their young to survive on, and no amount of it will ever be as good as a nutrient- and protein-rich, insect-based diet, the quality and abundance of which is influenced by urban green spaces. Even though a lot of people may not love having crows and magpies around, they are an important part of the ecosystem, and other animal species also benefit from green spaces in urban environments. This is something we humans can advocate for by demanding natural spaces be preserved in cities.

If you think you found an injured juvenile corvid on the ground, please make sure it is really injured or sick before attempting to call for rescue. When fledglings leave the nest, they spend a few days on the ground while they’re learning to fly, supervised by their parents. The bird you saw hopping around and not being able to fly well may just be trying their best in flight school.

If you find a dead bird, please report it to the regional CWHC office in your area. In Saskatchewan, you can contact the Western/Northern centre by phone at 306.966.5815 or by email at **@*******sf.ca.

Risks associated with the collection of specimens are low if reasonable sanitary precautions are taken, but some animals present more serious concerns than others, including venomous snakes, bats with potential rabies, and birds at risk for avian influenza. Your regional office can provide advice or guidance if needed. The Canadian Wildlife Health Cooperative website has specimen handling instructions on their website.

Written by: Beatriz Garcia de Sousa, CWHC Western/Northern

References

[1] Benmazouz, I., Jokimäki, J., Lengyel, S., Juhász, L., Kaisanlahti-Jokimäki, M.-L., Kardos, G., Paládi, P., & Kövér, L. (2021). Corvids in Urban Environments: A Systematic Global Literature Review. Animals, 11(11), 3226. https://doi.org/10.3390/ani11113226.

[2] Tangredi, B.P. (2007). Environmental factors associated with nutritional secondary hyperparathyroidism in wild birds. Avian and Poultry Biology Reviews, 18(2), 47-56. doi: 10.3184/147020607X251212

[3] Ciebiera, O., Czechowski, P., Morelli, F., Rubacha, S., & Jerzak, L. (2025). Adaptation of Eurasian Magpie (Pica pica) to Urban Environments: Population Dynamics and Habitat Preferences in Zielona Góra (Poland) over 23 Years. Animals, 15(5), 704. https://doi.org/10.3390/ani15050704.

[4] Kryštokofvá, M., Fousová, P., & Exnerová, A. (2011). Nestling diet of the Common Magpie (Pica pica) in urban and agricultural habitats. Ornis Fennica, 88(3), 138–146. https://doi.org/10.51812/of.133776.

The post A “Meal Deal” for Baby Birds – Is Human Junk Food Contributing to Malnutrition in Corvid Fledglings? appeared first on .