Posts Tagged ‘steve kroenke’

Last Nest and their Diminished Care

Monday, July 13th, 2009

The last nest is in the zone where nest checks are not advised. Fearing that I can flush out the 2 stronger birds and decrease their chances of survival, I have stopped supplemental feeding of the runt. I have seen the mother flying overhead and calling out but not actively feeding. Within the last week I have noticed a decrease from over a hundred birds flying about in the morning to none. Only about a dozen or so will stop by for several minutes at different parts of the morning. The season is ending quickly and the SY female is in a hurry to leave. Whether or not her instinct to stay and care for her young wins out over the instinct to join the flock and migrate, I am not sure. I hope the 2 larger and more robust nestlings make it but I doubt the runt can catch up now. This situation is a textbook example of something described as diminished parental care in some late nesting purple martins by a fellow PMCA forumite and purple martin landlord Mr. Steve Kroenke. You may have read this article on the forum but for my non-PMCA readers this is an issue that is fascinating if not tragic. With Mr. Kroenke’s permission I am posting his article here.


Diminishing Parental Care In Some Late Nesting Martins

Purple martins are a highly colonial and migratory species. They spend a good portion of their lives on the go, as they travel with other martins between their wintering grounds in South America and their nesting sites throughout the United States and Canada. So, the instinctive drive to migrate with the flock is deeply engrained in a martin’s genes and behavior. This drive is highly prevalent toward the end of the nesting season when nearly all martins have finished breeding and are forming pre-migratory flocks in preparation for the flight south. The urge to assemble and migrate south seems to dominate the purple martin species after the young have fledged and are independent. Martins have a long journey ahead of them and they must also finish molting all their feathers while on their wintering grounds. Migration instinct is extraordinarily strong in purple martins.

Competition Between Instinctive Drives In Late Nesting Purple Martins
This highly developed migratory drive will sometimes compete with a martin’s instinct to stay with its young, particularly when nearly all martins in the area have finished breeding and are heading south. Late nesting martins may be torn between the urge to migrate with the flock and the urge to continue staying behind and feeding their babies. When there is only one pair of nesting martins left at a colony, the conflict between the drives may be particularly strong. These are often, but not always, sub adult martins (SY) that have colonized a new site or are nesting at an older, established colony. When martins initiate such late nesting behavior, any young produced may be nest bound until late July into September depending on the geographical location of the colony. By this time, many martins are forming pre-migratory roosts or heading south. This may exert migratory pressures on these late nesting parent martins as they try to feed their young while suppressing their desire to fly with the flock and head south.
Late Nesting Martin Feeding Behavior/Parental Care
Most martins that are nesting during the “normal” breeding period for their area begin feeding their young at dawn, often while there are dim lighting conditions. They continue to feed their babies throughout the day, with occasional “slow down periods”, and persist until the evening. I have observed martins start feeding their babies just after 6:00 am and stop between 8:30 and 9:00 pm.
For very late nesting pairs, particularly those where all the other martins have finished breeding in the colony, you may observe significant variations from the “norm” relative to feeding young. Late nesting martins may vary considerably in their frequency and daily time frames of feedings to their young. If these late nesters are not roosting with their young, then the parents may arrive later in the mornings to begin feedings. I have observed some of these parents arrive at 8:00 am or later to begin feeding their young though most returned earlier. During the day, their feedings may be sporadic at times with the parents leaving the area during the late afternoon. Sometimes both parents will be gone when there are still several hours of daylight left to feed the young. I have observed some of these late nesting adults leave the area by 6:00 pm or even earlier. Both the beginning and ending feeding times for late nesting martins are greatly impacted by the age of the young and roosting behavior of the parents. If one or both of the parents are roosting with their babies, then you may see a more “normal” feeding schedule, starting early and ending before dark. However, even these roosting parents may start feeding their young later than normal.
When parent martins arrive late at the nest in the mornings and leave early in the afternoons, this behavior may relate to the distance they must fly to reach the closest pre-migratory roost site. If neither of the parents is roosting with the young, the adults are probably spending the night at the nearest pre-migratory roost. If it is late in the season and most martins are gone from the area, then there may be no nearby roosts, so the parent martins may be flying many miles to reach the closest one. This could result in several hours of flight time for the parent martins in the mornings to arrive at the nest and in the afternoons to reach the communal roost.

Also, late nesting martins must face much higher daytime temperatures and this factor can impact the number of feedings to the young. During extremely high temperatures in the upper 90s for example, insects, such as dragonflies, may not be flying in large numbers, thereby reducing the prey base for the parent martins. The young martins may become heat stressed and not be as responsive to the food stimulus.

And, just prior to fledging their young, parent martins will start reducing the daily feedings to prepare their babies’ transition from nestlings to fledglings. Hungry young are more prone to fledging than well fed ones, particularly when the parents tempt them with a dragonfly. So, it is normal to see fewer feedings during the last week prior to the young making their maiden flight.

There May Be Significant Differences In Feeding Behavior Between Male and Female Martins

From my observations of these very late nesting pairs, you may see significant gender differences between male and female martins in feeding their young. The female martin is clearly more attentive to the young and spends more time with her babies than her mate. This is largely a function of the specific gender roles in purple martin family life. The mother martin broods her young during their early lives and she usually roosts at night with the babies for much longer than the male. Some males may quit roosting with their families after the young are older and nearing fledging. For late nesting pairs, the males may quit roosting with their families soon after the young have hatched.

Late nesting male martins may show reduced parental care to their young by feeding them fewer times than normal and then leaving earlier in the day. This may become more pronounced after the young are about two weeks old and it is later in the breeding season. These males may arrive at the nest site later in the mornings and feed the young a few times. Then they may disappear for long periods and show up again later with an occasional food item. Generally, their feedings to the young may be lower than the females. Other males may function mainly as guardians to the nest and chase away other males, particularly SYs that try to enter the cavity. These males may stay around the nest site in the mornings and bring in an occasional dragonfly. Then they gradually disappear in the afternoons and will not return until the next day. Some males may eventually abandon their families after the young are older or just after fledging. I had several cases where the males finally just quit coming around and the female went solo to finish raising the young.

Female martins are extremely attentive to their young and closely bonded to them. Nurturing the young is a key gender role of the female martin. Females usually feed late hatching young reliably and provide good parental care. I never had a case where a female abandoned her late hatching young though some of these females may not feed their young as often as normally. Also, these females roosted with their babies almost up until fledging and some through that time. However, I did observe several situations where non-roosting females with older young would arrive late in the morning to start feeding their babies and then departed relatively early in the afternoon. In these cases, the females may have been flying many miles to reach a communal pre-migratory roost. Again, the females are usually much more bonded to their young than the males and provide better parental care in late nesting situations.

Differences Between Late Nesting ASY Pairs And SYs

Generally speaking late nesting ASY pairs, both male and female, are more attentive to their young and provide more reliable parental care. These martins have most likely successfully raised young in the past and this experience no doubt helps them. Late nesting ASY males are probably more prone to feed their babies at higher rates than the SYs. The SYs, particularly the males, are raising young for the first time and embarking on this most important and potentially stressful adventure late in nesting season does create a challenging situation. However, I have seen both late nesting ASY and SY males significantly reduce their feedings to their nest bound young and even on occasion abandon their family prior to the babies fledging.

Late Nesting Fledglings

When late nesting youngsters fledge, I have observed cases where the parents or female parent brought their young back to roost in their natal nest for several nights and in other situations where they all disappeared. However, I did have several cases where the females brought their young back for longer than a week. It is possible that these youngsters may have greater difficulties in surviving to independence since the parents are under pressure to migrate with the flock. This may result in reduced parental care after fledging. However, martin youngsters grow up fast and learn to hunt flying insects quickly. So, that is a good behavioral adaptation to possibly help martins overcome problems with fledging later in the nesting season.

Summary

Purple martins are highly migratory birds and are nomadic for a good portion of their lives. This powerfully developed drive to “go with the flock” at the end of the nesting season may sometimes conflict with an equally strong drive to feed late hatching young. This “battle of the instincts” may result in some parent martins, particularly the males, reducing their feedings to nest bound young or in rare cases abandoning their families. Most females tend to be more closely bonded to their young and often maintain a good level of parental care in late nesting situations. These females continue to feed their babies reliably, roost with them until fledging, and may bring them back to sleep in the evenings for several nights or longer.

by Steve Kroenke