Snail Kite Rostrhamus sociabilis

  • Order: Accipitriformes
  • Family: Accipitridae
  • Polytypic: 3 subspecies
  • Authors needed...
Sections

Breeding

Nests of the Snail Kite are usually in colonies with other nests of R. sociabilis or other species of waterbirds but can also be solitary. They are built in either woody or herbaceous vegetation close to or above the water and are typically a combination of dry sticks in the outside and green vegetation in the interior, comprising fifteen different species of plants as building material. Mean structure dimensions are: 22.7 cm in depth, 15.7 in cup diameter and 41.6 in width (Sykes, 1987). Studies done in Florida found that the most important factor affecting nest success, in addition to predation, is the substrate, since it plays a key role in structuring the nest and avoiding its collapse. Those built in woody vegetation such as willows have a higher success rate. Other factors such as water level, food availability and coloniality are interdependent with the type of substrate used or are less significant (Snyder et al., 1989), although hydrology certainly does influence adult and juvenile survival (Reichert et al., 2012).

Copulation occurs shortly after the nest is ready and continues until the clutch is complete (Sykes, 1987).

Clutch size may vary from 1 to 4 eggs, the most frequent number being 3 (Snyder et al., 1989). Since the female will lay an egg every two days, a nest containing three eggs will be complete in six days. Eggs are of a dull white color with brown markings and have an oblong oval or elliptical shape. They are in average 44.6 millimeters in length, 36.1 in breadth, 0.267 in thickness. Eggshell weight is 2.3 grams and whole egg weight is 31.7 grams when still fresh and 28.6 grams when incubation is complete (Sykes, 1987).
After the female lays the first egg, incubation by either parent begins and lasts, on average, 27.4 days (Sykes, 1987). One individual of the reproductive pair frequently deserts the nest by the time the eggs hatch and then finds another pair with whom it may reproduce and attend that new nest (Beissinger, 1990). However, nest success does not seem to be affected negatively by this behavior, but on the other hand is probably a way of enhancing offspring number in a system that has a high percentage of nest failure due to predation and nest collapse. So, the Snail Kite is iteroparous, and thus does not invest energy in a single brood but instead follows the strategy of laying a relatively low number of eggs that can be replaced during the long reproductive breeding season that varies from 5 to 10 months in South Florida (Beissinger, 1986) and other parts of its distribution such as Surinam (see Haverschmidt, 1970). The breeding season strongly coincides with peaks in the rainy season of the locality, although populations are asynchronous and thus breeding pairs living in sympatry are generally in different stages of their reproduction (Sykes, 1987).

Chicks fledge after about 23 to 28 days after hatching (Chandler et al., 1974) and nest success is on average 2.3 chicks per nest, which can vary in between seasons so it is higher in the wet season, when there is more food and less predation (Sykes, 1987).

Recommended Citation

Snail Kite (Rostrhamus sociabilis), In Neotropical Birds Online (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. retrieved from Neotropical Birds Online: https://neotropical.birds.cornell.edu/Species-Account/nb/species/snakit