SUMMARIZING INFORMATION ON NEST FATES

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After a nest has either fledged its young or failed it is necessary to condense the information from the nest visits into a summary that is useful for determining reproductive success of the nest, as well as provide population-level statistics such as daily mortality rates for a given species. In Arizona we conduct most of this summary work at the end of the field season.

After a nest is known to have fledged its offspring or failed, you may wish to prominently mark the exact location of the nest with flagging tape, labeled with the NST_ID#. This eases relocation of nests later in the season when field crews return to measure vegetation at and around nests. We have also found it useful to mark completed nests when using a global positioning system (GPS) unit to determine the exact locations of all nests on a study plot.

After The Field Season

After the field season, it is necessary to go over all of the information on the nest cards and determine several pieces of summary information that are needed by BBIRD. The following are the variables derived from data on nest visits. These are the actual nesting productivity variables that are reported to the BBIRD central data repository. Data should be reported on a nest by nest basis (one line in the database for each nest).

INITIATION DATE (INIT)

date that first egg laid

CLUTCH SIZE (CS)

the final number of eggs laid by the natal female in her nest. Record this only when the final number is known exactly. Otherwise leave CS blank, and record information in variable NFCS.

NON-FINAL CLUTCH SIZE (NFCS)

record clutch size information here, only if the final number of eggs could not be ascertained. Record a number in NFCS instead of CS when: 1) nests were found after hatching and you could use the number of nestings to estimate the minimum possible clutch size, 2) number of eggs was known on last nest check, but nest was subsequently depredated or abandoned and the adults may not have been finished laying on the previous check, or 3) observer could never confirm final clutch size and could only state that "at least # eggs in nest". If a group of fledglings are seen near the nest or actually fledging from the nest, this is not sufficient data to record a number for NFCS, unless you are certain that the observer saw ALL the fledglings. CS and NFCS are mutually exclusive. If you record a value for CS, then NFCS must be left blank, and vice versa.

NUMBER FLEDGED (NFLDG)

This variable is not recorded on the nest card, but is determined prior to data entry based on information recorded on nest card. During data entry, record the number of fledglings when number of young was counted in nest during second half of nestling period, or when a minimum number of fledglings were seen outside of nest. If an observer saw exact number of nestlings in first half only, leave NFLDG blank. If the observer saw fledglings then record the number of fledglings seen even if this number is less than the number of nestlings observed in first half. If nestlings were not observed during second half of nestling period and no fledglings were seen in area, leave this variable blank even if observer is certain that nest was successful.

EXACT NUMBER FLEDGED (EXNFLDG)

This variable is also not recorded on nest card. During data entry, code this variable as 1 when NFLDG represents an exact number, not an estimate. Code as 1 when the exact number of nestlings in nest was known within 2 days of fledging, otherwise leave blank.

LAYING SUCCESS (NSUCEGG)

success at completing egg laying; see nest fate codes.

INCUBATION SUCCESS (NSUCINC)

success at completing incubation; see nest fate codes. If nests failed during egg laying, this variable should be left blank.

NESTLING SUCCESS (NSUCNSTL)

success at completing nestling rearing; see nest fate codes. If the nest failed during laying or incubation, this variable should be left blank.

FINAL SUCCESS (NFINALSUC)

final outcome of nest, see fate codes. This code should mirror the code for the period in which the nest failed.

NUMBER DAYS UNDER OBSERVATION, LAYING (NOBEGG)

NUMBER DAYS UNDER OBSERVATION, INCUBATION (NOBINC)

NUMBER DAYS UNDER OBSERVATION, NESTLING REARING (NOBNSTL)

NUMBER DAYS UNDER OBSERVATION, STAGE UNKNOWN (NOBTOT)

number of days under observation that could not be assigned to a specific nesting stage. Leave blank if all observation days have been assigned to NOBEGG, NOBINC, and NOBNSTL.

EXACT INITIATION DATE (PRECINIT)

precision with which initiation date of egg laying is known. Code as 1 when date known exactly (first egg appeared between two reliable visits which were only 2 days apart); code 2 when date are derived from any reliably estimated period switch (e.g. INIT back calculated from known hatching date); code 3 when INIT was estimated from poor nest card information; code 4 used only for lower levels of stacked nests (e.g., Yellow Warbler nests parasitized by Brown-headed Cowbirds, and subsequently built over).

EXACT LAYING PERIOD (PRECLAY)

code as 1 when the number of days under observation during egg laying reflects the exact length of the egg laying period (you identified the day the first egg was laid and the day the last egg was laid). Code as 2 when your data span the entire nesting stage, but the exact transition days between the stages are unknown. If data cannot be coded as 1 or 2, leave these variables blank.

EXACT INCUBATION PERIOD (PRECINC)

code as 1 when the number of days under observation during incubation reflects the exact length of the incubation period (you identified the first day of incubation and the hatch date). Code as either 2 or leave blank according to the same criteria as for EXACT LAYING PERIOD.

EXACT NESTLING PERIOD (PRECNSTL)

code as 1 when the number of days under observation during the nestling period reflects the exact length of the nestling period (you identified the hatch date and the fledging date). Code as either 2 or leave blank according to the same criteria for EXACT LAYING PERIOD.

NUMBER OF COWBIRD EGGS LAID (CEGGLAY)

DATE OF FIRST BHCO EGG APPEARANCE (CEGGDATE)

NUMBER OF COWBIRDS HATCHED (CEGGHTCH)

NUMBER OF COWBIRDS FLEDGED (CFLDG)

FATE OF COWBIRDS (CNFATE)

the cowbird equivalent of NFINALSUC. See fate codes.

TIMING OF COWBIRD FATE (CFATETIM)

timing of cowbirds' fate, relative to host young (1 = before host offspring, 2 = same time as host offspring, 3 = after host offspring)

NUMBER DAYS UNDER OBSERVATION, COWBIRDS (COBS)

total observation days for cowbirds (may be longer than for host young if these die before fledging).

EXACT COWBIRD INITIATION (PRECEGGD)

precision with which cowbird egg laying date was estimated. Use same codes as for PRECINIT, above.

EXACT COWBIRD CLUTCH SIZE (PRECEGGL)

precision with which number of cowbird eggs in nest is known. Codes as 1 when eggs seen clearly in incubation, code as 2 when eggs only seen in egg laying, codes as 3 only cowbird nestlings seen, or code as 4 when only fledgling cowbirds seen with host parents. All codes other than 1 indicate that CEGGLAY is a minimum estimate.

EXACT NUMBER COWBIRDS HATCHED (PRECEGGH)

precision with which number of number of cowbird hatchlings known. Code as 1 when the number of cowbird eggs to hatch is clearly known, or the number of cowbird eggs and number of cowbird fledglings is equal; codes as 2 when the last count of the number of cowbird eggs was made during egg laying and the number of fledgling cowbirds is known; code as 3 when the only count of cowbirds is during the nestling stage; code as 4 when the only count of cowbirds is after fledging.

EXACT NUMBER COWBIRD FLEDGLINGS (PRECFLDG)

precision with which number of cowbird fledglings is known. Code of 1 is the same as for EXNFLDG, code 2 if nestling cowbirds seen more than 2 days before fledging, code as 3 if only cowbird eggs counted but fledglings seen, code as 4 when only the number of fledglings was counted.

PARENTAL ELUSIVENESS (ELUSIVE)

How the adult acts around the nest before becoming disturbed. The value of ELUSIVE that you report is the average value of all visits combined (to the nearest 0.1).

Nest Fate Codes

The variables SUCLAY, SUCEGG, SUCNSTL, FINALSUC, and CFATE are given numeric codes which allow data analysts to quickly sort through the BBIRD database and determine causes of failure of nests. These codes are in the form of decimal numbers, in which the integer portion places a nest into one of several broad classes, and the decimal portion of the code indicates in more detail what caused the fate. NOTE: the way in which we code fates has changed from previous years; see APPENDIX C for a list of the translations from old to new fate codes. In the table below "prefix" will be used to refer to the integer number that describes the general class of fates, and "suffix" will refer to the decimal place modifier of the general fate class. Here are the new BBIRD fate codes:

TABLE: FATE CODES FOR NESTING SUCCESS

Prefix	Definition of Prefix	Allowable Suffixes	Definition of Suffix
1	Nest successfully completed stage of reproductive cycle
		0	No modifiers allowed
2	Nest failed during stage of nesting cycle due to any other cause except cowbird parasitism.
		0	Cause unknown
		1	Abandoned before eggs were laid -- use only when certain no eggs were laid. Do not use this nest when calculating Mayfield failure rates of nests.
		2	Abandoned after first egg laid -- use only when certain that at least one egg was laid.
		3	Depredated
		4	Failed due to adult mortality -- a strong possibility when nest abandoned for no apparent reason late in incubation or nestling rearing.
		5	Failed due to research activities -- any nest failure directly attributable to research work
		6	Failed due t o weather (e.g. wind, hail, high winds)
		7	Failed due t o Acts of God (e.g. nest tree falling down, moose laying down on nest, nest tree struck by lightening, floods)
3	Brood parasitism caused failure -- use for fates of host young in any case of parasitism, unless natal young successful
		0	Either natal or parasite eggs abandoned by natal parents
		1	Natal young failed, but parasite young survived longer (whether or not parasites fledged)
		2	Fate of natal offspring unknown, but parasite offspring definitely survived longer (regardless of whether they fledged)
4	Status unknown -- these nests are not used in Mayfield estimates
		0	Nest found, but never observed occupied or active (i.e. old or previously abandoned)
		1	Nest occupied, but information not sufficient to determine fate
		2	Nest occupied, but monitoring discontinued

Calculating Days Under Observation And Initiation Date

Complete information on nesting chronology is rare, so we frequently have to estimate the number of days that a nest was under observation at each stage of the nesting period. Here are some rules to follow:

1. Incubation starts when the last egg is laid (i.e. the last day of egg laying should be counted as the first day of incubation and NOT as a day of egg laying). I.e., the number of days in the laying period will generally be one less than the clutch size.
2. The nestling period starts when the first egg hatches
3. The day you find a nest is the first day under observation or the day the first egg is laid if the nest is found during building (estimates of percent nest completion are useful to estimate when the first egg should be laid).
4. In general, we use the mid-point between nest visits to estimate when critical events in the nesting cycle occurred (e.g., nest stage transitions, fledging, or failure). Examples: If a nest was being incubated on 6/4, and eggs had hatched by the next check on 6/7; estimated hatch date would be midnight on 6/5 (see figure, below). Assume that the nest is checked again on 6/11 and it has been depredated. Estimated failure time would be noon on 6/9, and days under observation during the nestling period would be 3.5 days. Estimate days under observation to the nearest half day. When nest visits are several days apart, the mid-point between visits can be a very inaccurate estimate of when an event occurred. The range of possible days can sometimes be narrowed by using data on age of the young, and/or normal lengths of the incubation and nestling periods from the literature.

               check             check                   check
                 |                 |                       |
              |_____|_____|_____|_____|_____|_____|_____|_____|
                 4     5     6     7     8     9     10    11
                              |_____________________| 
                             est      3½ days      est 
                            hatch                 fail