Tuesday, 15 June 2010
Sorry, I couldn't resist the media-like headline! But it does sum it up quite well. The weekend was a success for the birds at the Oysterbeds. More of the clutches of Common Tern eggs hatched and, up until late yesterday evening, all of the adults that had hatched young still had some or all of their family. There are plenty of broods of two and three young. In fact, Sunday gave me an opportunity to count pretty much all of the young chicks as the adults kept coming and going to feed them. The final tallies were: 80 pairs nesting; 46 pairs with young; at least 104 young including 16 broods of three. It was too windy yesterday to establish comparative numbers after another 24 hours but at least three more clutches had hatched.
From a predators viewpoint all these chicks are potential food packages. In effect, the islands in the lagoon are currently a natural fast-food restaurant ready to be turned into a take away by any hungry predator! One worrying aspect of the weather at the moment is the wind strength. This makes finding food for the terns more difficult, and both adults will more often leave the chicks 'home alone' to find food for them, this exposing them to increased chances of avian predation (in this case, gulls). Once again, as one day last week, I noticed that in the moderate breeze of yesterday more of the food items being bought back to the colony and fed to the chicks were tiny flat fish rather than slender (and easier-to-swallow) silvery fish.
I have provided some artificial shelters for the chicks. These are just simple constructions of wood that were placed close to individual nests. Already by Sunday several of these shelters (there are nine in all) were being used by tern chicks. I watched one chick disappear into the darkness of one (an upturned V-shaped shelter with a peak of about 20 centimeters) only to scamper out, like a starving clockwork Gremlin, when it saw that its siblings were being fed by dad!
Mediterranean Gulls continue to provide a threat to the chicks, and yesterday evening I witnessed, for a third time recently, an adult patrol the colony and leave with a stray gull egg. It could easily have been a tern chick. They need to grow fast to reduce their risk of predation from Med Gulls.
The Oystercatchers on South Island lost one of their chicks last Thursday night/Friday morning. I'm not sure why, but a proportion of wader chicks do seem to die in their third day of life. This may be because they never learn to feed properly and, once their post-hatching energy resources are used up, they perish. The remaining chick seems to be doing well. Oystercatchers are very good attentive parents and bring in fresh food for their young. This is unusual for a species of wader. Most wader chicks learn to feed for themselves within hours of hatching. Oystercatchers learn very slowly, and are fed right up until and often after fledging by both parents, predominantly the male to begin with. As well as feeding on worms, they feed on crustaceans and shellfish such as crabs, cockles and clams. The skills needed to crack the shell of a cockle and prize the contents out are learned. I have seen juveniles, fledged in August, still begging for food from their parents in October. Worms form the staple diet of these younger, inexperienced birds.
Sorry, I couldn't resist the media-like headline! But it does sum it up quite well. The weekend was a success for the birds at the Oysterbeds. More of the clutches of Common Tern eggs hatched and, up until late yesterday evening, all of the adults that had hatched young still had some or all of their family. There are plenty of broods of two and three young. In fact, Sunday gave me an opportunity to count pretty much all of the young chicks as the adults kept coming and going to feed them. The final tallies were: 80 pairs nesting; 46 pairs with young; at least 104 young including 16 broods of three. It was too windy yesterday to establish comparative numbers after another 24 hours but at least three more clutches had hatched.
From a predators viewpoint all these chicks are potential food packages. In effect, the islands in the lagoon are currently a natural fast-food restaurant ready to be turned into a take away by any hungry predator! One worrying aspect of the weather at the moment is the wind strength. This makes finding food for the terns more difficult, and both adults will more often leave the chicks 'home alone' to find food for them, this exposing them to increased chances of avian predation (in this case, gulls). Once again, as one day last week, I noticed that in the moderate breeze of yesterday more of the food items being bought back to the colony and fed to the chicks were tiny flat fish rather than slender (and easier-to-swallow) silvery fish.
I have provided some artificial shelters for the chicks. These are just simple constructions of wood that were placed close to individual nests. Already by Sunday several of these shelters (there are nine in all) were being used by tern chicks. I watched one chick disappear into the darkness of one (an upturned V-shaped shelter with a peak of about 20 centimeters) only to scamper out, like a starving clockwork Gremlin, when it saw that its siblings were being fed by dad!
Mediterranean Gulls continue to provide a threat to the chicks, and yesterday evening I witnessed, for a third time recently, an adult patrol the colony and leave with a stray gull egg. It could easily have been a tern chick. They need to grow fast to reduce their risk of predation from Med Gulls.
The Oystercatchers on South Island lost one of their chicks last Thursday night/Friday morning. I'm not sure why, but a proportion of wader chicks do seem to die in their third day of life. This may be because they never learn to feed properly and, once their post-hatching energy resources are used up, they perish. The remaining chick seems to be doing well. Oystercatchers are very good attentive parents and bring in fresh food for their young. This is unusual for a species of wader. Most wader chicks learn to feed for themselves within hours of hatching. Oystercatchers learn very slowly, and are fed right up until and often after fledging by both parents, predominantly the male to begin with. As well as feeding on worms, they feed on crustaceans and shellfish such as crabs, cockles and clams. The skills needed to crack the shell of a cockle and prize the contents out are learned. I have seen juveniles, fledged in August, still begging for food from their parents in October. Worms form the staple diet of these younger, inexperienced birds.
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